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1
Betts, A. K. "FIFE atmospheric boundary layer budget methods." Journal of Geophysical Research 97, no. D17 (1992): 18523. http://dx.doi.org/10.1029/91jd03172.
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Prados-Roman, C., C. A. Cuevas, T. Hay, R. P. Fernandez, A. S. Mahajan, S. J. Royer, M. Galí, et al. "Iodine oxide in the global marine boundary layer." Atmospheric Chemistry and Physics 15, no. 2 (January 16, 2015): 583–93. http://dx.doi.org/10.5194/acp-15-583-2015.
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Abstract. Emitted mainly by the oceans, iodine is a halogen compound important for atmospheric chemistry due to its high ozone depletion potential and effect on the oxidizing capacity of the atmosphere. Here we present a comprehensive data set of iodine oxide (IO) measurements in the open marine boundary layer (MBL) made during the Malaspina 2010 circumnavigation. Results show IO mixing ratios ranging from 0.4 to 1 pmol mol−1 (30% uncertainty) and, complemented with additional field campaigns, this data set confirms through observations the ubiquitous presence of reactive iodine chemistry in the global marine environment. We use a global model with organic (CH3I, CH2ICl, CH2I2 and CH2IBr) and inorganic (HOI and I2) iodine ocean emissions to investigate the contribution of the different iodine source gases to the budget of IO in the global MBL. In agreement with previous estimates, our results indicate that, globally averaged, the abiotic precursors contribute about 75 % to the IO budget. However, this work reveals a strong geographical pattern in the contribution of organic vs. inorganic precursors to reactive iodine in the global MBL.
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Chamecki, Marcelo, Livia S. Freire, Nelson L. Dias, Bicheng Chen, Cléo Quaresma Dias-Junior, Luiz Augusto Toledo Machado, Matthias Sörgel, Anywhere Tsokankunku, and Alessandro C. de Araújo. "Effects of Vegetation and Topography on the Boundary Layer Structure above the Amazon Forest." Journal of the Atmospheric Sciences 77, no. 8 (August 1, 2020): 2941–57. http://dx.doi.org/10.1175/jas-d-20-0063.1.
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Abstract Observational data from two field campaigns in the Amazon forest were used to study the vertical structure of turbulence above the forest. The analysis was performed using the reduced turbulent kinetic energy (TKE) budget and its associated two-dimensional phase space. Results revealed the existence of two regions within the roughness sublayer in which the TKE budget cannot be explained by the canonical flat-terrain TKE budgets in the canopy roughness sublayer or in the lower portion of the convective ABL. Data analysis also suggested that deviations from horizontal homogeneity have a large contribution to the TKE budget. Results from LES of a model canopy over idealized topography presented similar features, leading to the conclusion that flow distortions caused by topography are responsible for the observed features in the TKE budget. These results support the conclusion that the boundary layer above the Amazon forest is strongly impacted by the gentle topography underneath.
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Raymond, D. J., and C. López Carrillo. "The vorticity budget of developing typhoon Nuri (2008)." Atmospheric Chemistry and Physics 11, no. 1 (January 10, 2011): 147–63. http://dx.doi.org/10.5194/acp-11-147-2011.
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Abstract. The formation of west Pacific tropical cyclone Nuri (2008) was observed over four days from easterly wave to typhoon stage by aircraft using scanning Doppler radar and dropsonde data. This disturbance developed rapidly in a significantly sheared environment. In spite of the shear, overlapping closed circulations existed in the frame of reference of the storm in the planetary boundary layer and at 5 km elevation, providing a deep region protected from environmental influences. The rapid spinup of Nuri can be attributed to the strong increase with height at low levels of the vertical mass flux during and after the tropical depression stage, and the correspondingly strong vorticity convergence in the planetary boundary layer. As Nuri developed, convective regions of boundary layer vortex stretching became fewer but more intense, culminating in a single nascent eyewall at the tropical storm stage. A non-developing tropical wave case was also analyzed. This system started with much weaker circulations in the boundary layer and aloft, leaving it unprotected against environmental intrusion. This may explain its failure to develop.
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Stieger, J., I. Bamberger, N. Buchmann, and W. Eugster. "Validation of farm-scale methane emissions using nocturnal boundary layer budgets." Atmospheric Chemistry and Physics 15, no. 24 (December 21, 2015): 14055–69. http://dx.doi.org/10.5194/acp-15-14055-2015.
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Abstract. This study provides the first experimental validation of Swiss agricultural methane emission estimates at the farm scale. We measured CH4 concentrations at a Swiss farmstead during two intensive field campaigns in August 2011 and July 2012 to (1) quantify the source strength of livestock methane emissions using a tethered balloon system and (2) to validate inventory emission estimates via nocturnal boundary layer (NBL) budgets. Field measurements were performed at a distance of 150 m from the nearest farm buildings with a tethered balloon system in combination with gradient measurements at eight heights on a 10 m tower to better resolve the near-surface concentrations. Vertical profiles of air temperature, relative humidity, CH4 concentration, wind speed, and wind direction showed that the NBL was strongly influenced by local transport processes and by the valley wind system. Methane concentrations showed a pronounced time course, with highest concentrations in the second half of the night. NBL budget flux estimates were obtained via a time–space kriging approach. Main uncertainties of NBL budget flux estimates were associated with nonstationary atmospheric conditions and the estimate of the inversion height zi (top of volume integration). The mean NBL budget fluxes of 1.60 ± 0.31 μg CH4 m-2 s-1 (1.40 ± 0.50 and 1.66 ± 0.20 μg CH4 m-2 s-1 in 2011 and 2012 respectively) were in good agreement with local inventory estimates based on current livestock number and default emission factors, with 1.29 ± 0.47 and 1.74 ± 0.63 μg CH4 m-2 s-1 for 2011 and 2012 respectively. This indicates that emission factors used for the national inventory reports are adequate, and we conclude that the NBL budget approach is a useful tool to validate emission inventory estimates.
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Prados-Roman, C., C. A. Cuevas, T. Hay, R. P. Fernandez, A. S. Mahajan, S. J. Royer, M. Galí, et al. "Iodine oxide in the global marine boundary layer." Atmospheric Chemistry and Physics Discussions 14, no. 15 (August 29, 2014): 22217–43. http://dx.doi.org/10.5194/acpd-14-22217-2014.
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Abstract. Emitted mainly by the oceans, iodine is a halogen compound important for atmospheric chemistry due to its high ozone depletion potential and effect on the oxidizing capacity of the atmosphere. Here we present a comprehensive dataset of iodine oxide (IO) measurements in the open marine boundary layer (MBL) made during the Malaspina 2010 circumnavigation. Results show IO mixing ratios ranging from 0.4 to 1 pmol mol−1 and, complemented with additional field campaigns, this dataset confirms through observations the ubiquitous presence of reactive iodine chemistry in the global marine environment. We use a global model with organic (CH3I, CH2ICl, CH2I2 and CH2IBr) and inorganic (HOI and I2) iodine ocean emissions to investigate the contribution of the different iodine source gases to the budget of IO in the global MBL. In agreement with previous estimates, our results indicate that, globally averaged, the abiotic precursors contribute about 75% to the iodine oxide budget. However, this work reveals a strong geographical pattern in the contribution of organic vs. inorganic precursors to reactive iodine in the global MBL.
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Caldwell, Peter, Christopher S. Bretherton, and Robert Wood. "Mixed-Layer Budget Analysis of the Diurnal Cycle of Entrainment in Southeast Pacific Stratocumulus." Journal of the Atmospheric Sciences 62, no. 10 (October 1, 2005): 3775–91. http://dx.doi.org/10.1175/jas3561.1.
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Abstract Mixed-layer budgets of boundary layer mass, moisture, and liquid water static energy are estimated from 6 days of data collected at 20°S, 85°W (a region of persistent stratocumulus) during the East Pacific Investigation of Climate (EPIC) stratocumulus cruise in 2001. These budgets are used to estimate a mean diurnal cycle of entrainment and, by diagnosing the fluxes of humidity and liquid water static energy necessary to maintain a mixed-layer structure, of buoyancy flux. Although the entrainment rates suggested by each of the budgets have significant uncertainty, the various methods are consistent in predicting a 6-day mean entrainment rate of 4 ± 1 mm s−1, with higher values at night and very little entrainment around local noon. The diurnal cycle of buoyancy flux suggests that drizzle, while only a small term in the boundary layer moisture budget, significantly reduces subcloud buoyancy flux and may induce weak decoupling of surface and cloud-layer turbulence during the early morning hours, a structure that is maintained throughout the day by shortwave warming. Finally, the diurnal cycle of entrainment diagnosed from three recently proposed entrainment closures is found to be consistent with the observationally derived values.
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Monahan, Adam Hugh. "The Probability Distribution of Sea Surface Wind Speeds: Effects of Variable Surface Stratification and Boundary Layer Thickness." Journal of Climate 23, no. 19 (October 1, 2010): 5151–62. http://dx.doi.org/10.1175/2010jcli3184.1.
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Abstract Air–sea exchanges of momentum, energy, and material substances of fundamental importance to the variability of the climate system are mediated by the character of the turbulence in the atmospheric and oceanic boundary layers. Sea surface winds influence, and are influenced by, these fluxes. The probability density function (pdf) of sea surface wind speeds p(w) is a mathematical object describing the variability of surface winds that arises from the physics of the turbulent atmospheric planetary boundary layer. Previous mechanistic models of the pdf of sea surface wind speeds have considered the momentum budget of an atmospheric layer of fixed thickness and neutral stratification. The present study extends this analysis, using an idealized model to consider the influence of boundary layer thickness variations and nonneutral surface stratification on p(w). It is found that surface stratification has little direct influence on p(w), while variations in boundary layer thickness bring the predictions of the model into closer agreement with the observations. Boundary layer thickness variability influences the shape of p(w) in two ways: through episodic downward mixing of momentum into the boundary layer from the free atmosphere and through modulation of the importance (relative to other tendencies) of turbulent momentum fluxes at the surface and the boundary layer top. It is shown that the second of these influences dominates over the first.
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Nilsson, Erik, Marie Lothon, Fabienne Lohou, Eric Pardyjak, Oscar Hartogensis, and Clara Darbieu. "Turbulence kinetic energy budget during the afternoon transition – Part 2: A simple TKE model." Atmospheric Chemistry and Physics 16, no. 14 (July 19, 2016): 8873–98. http://dx.doi.org/10.5194/acp-16-8873-2016.
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Abstract. A simple model for turbulence kinetic energy (TKE) and the TKE budget is presented for sheared convective atmospheric conditions based on observations from the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign. It is based on an idealized mixed-layer approximation and a simplified near-surface TKE budget. In this model, the TKE is dependent on four budget terms (turbulent dissipation rate, buoyancy production, shear production and vertical transport of TKE) and only requires measurements of three available inputs (near-surface buoyancy flux, boundary layer depth and wind speed at one height in the surface layer) to predict vertical profiles of TKE and TKE budget terms.This simple model is shown to reproduce some of the observed variations between the different studied days in terms of near-surface TKE and its decay during the afternoon transition reasonably well. It is subsequently used to systematically study the effects of buoyancy and shear on TKE evolution using idealized constant and time-varying winds during the afternoon transition. From this, we conclude that many different TKE decay rates are possible under time-varying winds and that generalizing the decay with simple scaling laws for near-surface TKE of the form tα may be questionable.The model's errors result from the exclusion of processes such as elevated shear production and horizontal advection. The model also produces an overly rapid decay of shear production with height. However, the most influential budget terms governing near-surface TKE in the observed sheared convective boundary layers are included, while only second-order factors are neglected. Comparison between modeled and averaged observed estimates of dissipation rate illustrates that the overall behavior of the model is often quite reasonable. Therefore, we use the model to discuss the low-turbulence conditions that form first in the upper parts of the boundary layer during the afternoon transition and are only apparent later near the surface. This occurs as a consequence of the continuous decrease in near-surface buoyancy flux during the afternoon transition. This region of weak afternoon turbulence is hypothesized to be a “pre-residual layer”, which is important in determining the onset conditions for the weak sporadic turbulence that occur in the residual layer once near-surface stratification has become stable.
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Zhang, Jun A., William M. Drennan, Peter G. Black, and Jeffrey R. French. "Turbulence Structure of the Hurricane Boundary Layer between the Outer Rainbands." Journal of the Atmospheric Sciences 66, no. 8 (August 1, 2009): 2455–67. http://dx.doi.org/10.1175/2009jas2954.1.
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Abstract As part of the Coupled Boundary Layers Air–Sea Transfer (CBLAST)-Hurricane program, flights were conducted to directly measure turbulent fluxes and turbulence properties in the high-wind boundary layer of hurricanes between the outer rainbands. For the first time, vertical profiles of normalized momentum fluxes, sensible heat and humidity fluxes, and variances of three-dimensional wind velocities and specific humidity are presented for the hurricane boundary layer with surface wind speeds ranging from 20 to 30 m s−1. The turbulent kinetic energy budget is estimated, indicating that the shear production and dissipation are the major source and sink terms, respectively. The imbalance in the turbulent kinetic energy budget indicates that the unmeasured terms, such as horizontal advection, may be important in hurricane boundary layer structure and dynamics. Finally, the thermodynamic boundary layer height, estimated based on the virtual potential temperature profiles, is roughly half of the boundary layer height estimated from the momentum flux profiles. The latter height where momentum and humidity fluxes tend to vanish is close to that of the inflow layer and also of the maximum in the tangential velocity profiles.
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McGrath-Spangler, E. L., A. S. Denning, K. D. Corbin, and I. T. Baker. "Implementation of a boundary layer heat flux parameterization into the Regional Atmospheric Modeling System (RAMS)." Atmospheric Chemistry and Physics Discussions 8, no. 4 (July 25, 2008): 14311–46. http://dx.doi.org/10.5194/acpd-8-14311-2008.
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Abstract. The response of atmospheric carbon dioxide to a given amount of surface flux is inversely proportional to the depth of the boundary layer. Overshooting thermals that entrain free tropospheric air down into the boundary layer modify the characteristics and depth of the lower layer through the insertion of energy and mass. This alters the surface energy budget by changing the Bowen ratio and thereby altering the vegetative response and the surface boundary conditions. Although overshooting thermals are important in the physical world, their effects are unresolved in most regional models. A parameterization to include the effects of boundary layer entrainment was introduced into a coupled ecosystem-atmosphere model (SiB-RAMS). The parameterization is based on a downward heat flux at the top of the boundary layer that is proportional to the heat flux at the surface. Results with the parameterization show that the boundary layer simulated is deeper, warmer, and drier than when the parameterization is turned off. These results alter the vegetative stress factors thereby changing the carbon flux from the surface. The combination of this and the deeper boundary layer change the concentration of carbon dioxide in the boundary layer.
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Martínez, G. M., F. Valero, and L. Vázquez. "The TKE budget in the convective Martian planetary boundary layer." Quarterly Journal of the Royal Meteorological Society 137, no. 661 (August 12, 2011): 2194–208. http://dx.doi.org/10.1002/qj.883.
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Dong, Shenfu, Sarah T. Gille, and Janet Sprintall. "An Assessment of the Southern Ocean Mixed Layer Heat Budget." Journal of Climate 20, no. 17 (September 1, 2007): 4425–42. http://dx.doi.org/10.1175/jcli4259.1.
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Abstract The mixed layer heat balance in the Southern Ocean is examined by combining remotely sensed measurements and in situ observations from 1 June 2002 to 31 May 2006, coinciding with the period during which Advanced Microwave Scanning Radiometer-Earth Observing System (EOS) (AMSR-E) sea surface temperature measurements are available. Temperature/salinity profiles from Argo floats are used to derive the mixed layer depth. All terms in the heat budget are estimated directly from available data. The domain-averaged terms of oceanic heat advection, entrainment, diffusion, and air–sea flux are largely consistent with the evolution of the mixed layer temperature. The mixed layer temperature undergoes a strong seasonal cycle, which is largely attributed to the air–sea heat fluxes. Entrainment plays a secondary role. Oceanic advection also experiences a seasonal cycle, although it is relatively weak. Most of the seasonal variations in the advection term come from the Ekman advection, in contrast with western boundary current regions where geostrophic advection controls the total advection. Substantial imbalances exist in the regional heat budgets, especially near the northern boundary of the Antarctic Circumpolar Current. The biggest contributor to the surface heat budget error is thought to be the air–sea heat fluxes, because only limited Southern Hemisphere data are available for the reanalysis products, and hence these fluxes have large uncertainties. In particular, the lack of in situ measurements during winter is of fundamental concern. Sensitivity tests suggest that a proper representation of the mixed layer depth is important to close the budget. Salinity influences the stratification in the Southern Ocean; temperature alone provides an imperfect estimate of mixed layer depth and, because of this, also an imperfect estimate of the temperature of water entrained into the mixed layer from below.
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van de Berg, W. J., M. R. van den Broeke, and E. van Meijgaard. "Spatial structures in the heat budget of the Antarctic Atmospheric Boundary Layer." Cryosphere Discussions 1, no. 1 (August 15, 2007): 271–301. http://dx.doi.org/10.5194/tcd-1-271-2007.
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Abstract. Output from the regional climate model RACMO2/ANT is used to calculate the heat budget of the Antarctic atmospheric boundary layer (ABL). The main feature of the wintertime Antarctic ABL is a persistent temperature deficit compared to the free atmosphere. The magnitude of this deficit is controlled by the heat budget. During winter, transport of heat towards the surface by turbulence and net longwave emission are the primary ABL cooling terms. These processes show horizontal spatial variability only on continental scales. Vertical and horizontal advection of heat are the main warming terms. Over regions with convex ice sheet topography, i.e. domes and ridges, warming by downward vertical advection is enhanced due to divergence of the ABL wind field. Horizontal advection balances any excess warming caused by vertical advection, hence the ABL over domes and ridges tends to have a relatively weak temperature deficit. Conversely, vertical advection is reduced in regions with concave topography, i.e. valleys, where the ABL temperature deficit is enlarged. Along the coast, horizontal and vertical advection is governed by the inability of the large-scale circulation to adapt to small scale topographic features. Meso-scale (~10 km) topographic structures have thus a strong impact on the ABL winter temperature, besides latitude and surface elevation. During summer, this mechanism is much weaker; and the horizontal variability of ABL temperatures is smaller.
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van de Berg, W. J., M. R. van den Broeke, and E. van Meijgaard. "Spatial structures in the heat budget of the Antarctic atmospheric boundary layer." Cryosphere 2, no. 1 (January 8, 2008): 1–12. http://dx.doi.org/10.5194/tc-2-1-2008.
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Abstract. Output from the regional climate model RACMO2/ANT is used to calculate the heat budget of the Antarctic atmospheric boundary layer (ABL). The main feature of the wintertime Antarctic ABL is a persistent temperature deficit compared to the free atmosphere. The magnitude of this deficit is controlled by the heat budget. During winter, transport of heat towards the surface by turbulence and net longwave emission are the primary ABL cooling terms. These processes show horizontal spatial variability only on continental scales. Vertical and horizontal, i.e. along-slope, advection of heat are the main warming terms. Over regions with convex ice sheet topography, i.e. domes and ridges, warming by downward vertical advection is enhanced due to divergence of the ABL wind field. Horizontal advection balances excess warming caused by vertical advection, hence the temperature deficit in the ABL weakens over domes and ridges along the prevailing katabatic wind. Conversely, vertical advection is reduced in regions with concave topography, i.e. valleys, where the ABL temperature deficit enlarges along the katabatic wind. Along the coast, horizontal and vertical advection is governed by the inability of the large-scale circulation to adapt to small scale topographic features. Meso-scale topographic structures have thus a strong impact on the ABL winter temperature, besides latitude and surface elevation. During summer, this mechanism is much weaker, and the horizontal variability of ABL temperatures is smaller.
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Wang, Hui, Chun-Chieh Wu, and Yuqing Wang. "Secondary Eyewall Formation in an Idealized Tropical Cyclone Simulation: Balanced and Unbalanced Dynamics." Journal of the Atmospheric Sciences 73, no. 10 (September 21, 2016): 3911–30. http://dx.doi.org/10.1175/jas-d-15-0146.1.
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Abstract The secondary eyewall formation (SEF) in an idealized simulation of a tropical cyclone (TC) is examined from the perspective of both the balanced and unbalanced dynamics and through the tangential wind (Vt) budget analysis. It is found that the expansion of the azimuthal-mean Vt above the boundary layer occurs prior to the development of radial moisture convergence in the boundary layer. The Vt expansion results primarily from the inward angular momentum transport by the mid- to lower-tropospheric inflow induced by both convective and stratiform heating in the spiral rainbands. In response to the Vt broadening is the development of radial inflow convergence and the supergradient flow near the top of the inflow boundary layer. Results from the Vt budget analysis show that the combined effect of the mean advection and the surface friction is to spin down Vt in the boundary layer, while the eddy processes (eddy radial and vertical advection) contribute positively to the spinup of Vt in the SEF region in the boundary layer. Therefore, eddies play an important role in the spinup of Vt in the boundary layer during SEF. The balanced Sawyer–Eliassen solution can well capture the secondary circulation in the full-physics model simulation. The radial inflow diagnosed from the Sawyer–Eliassen equation is shown to spin up Vt and maintain the vortex above the boundary layer. However, the axisymmetric balanced dynamics cannot explain the spinup of Vt in the boundary layer, which results mainly from the eddy processes.
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Meskhidze, Nicholas, Matthew Salter, Karine Sellegri, and Scott Elliott. "Ocean Contributions to the Marine Boundary Layer Aerosol Budget." Atmosphere 10, no. 2 (February 23, 2019): 98. http://dx.doi.org/10.3390/atmos10020098.
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Kay, J. E., K. Raeder, A. Gettelman, and J. Anderson. "The Boundary Layer Response to Recent Arctic Sea Ice Loss and Implications for High-Latitude Climate Feedbacks." Journal of Climate 24, no. 2 (January 15, 2011): 428–47. http://dx.doi.org/10.1175/2010jcli3651.1.
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Abstract This study documents and evaluates the boundary layer and energy budget response to record low 2007 sea ice extents in the Community Atmosphere Model version 4 (CAM4) using 1-day observationally constrained forecasts and 10-yr runs with a freely evolving atmosphere. While near-surface temperature and humidity are minimally affected by sea ice loss in July 2007 forecasts, near-surface stability decreases and atmospheric humidity increases aloft over newly open water in September 2007 forecasts. Ubiquitous low cloud increases over the newly ice-free Arctic Ocean are found in both the July 2007 and the September 2007 forecasts. In response to the 2007 sea ice loss, net surface [top of the atmosphere (TOA)] energy budgets change by +19.4 W m−2 (+21.0 W m−2) and −17.9 W m−2 (+1.4 W m−2) in the July 2007 and September 2007 forecasts, respectively. While many aspects of the forecasted response to sea ice loss are consistent with physical expectations and available observations, CAM4’s ubiquitous July 2007 cloud increases over newly open water are not. The unrealistic cloud response results from the global application of parameterization designed to diagnose stratus clouds based on lower-tropospheric stability (CLDST). In the Arctic, the well-mixed boundary layer assumption implicit in CLDST is violated. Requiring a well-mixed boundary layer to diagnose stratus clouds improves the CAM4 cloud response to sea ice loss and increases July 2007 surface (TOA) energy budgets over newly open water by +11 W m−2 (+14.9 W m−2). Of importance to high-latitude climate feedbacks, unrealistic stratus cloud compensation for sea ice loss occurs only when stable and dry atmospheric conditions exist. Therefore, coupled climate projections that use CAM4 will underpredict Arctic sea ice loss only when dry and stable summer conditions occur.
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Dupont, Sylvain, Patrice G. Mestayer, Emmanuel Guilloteau, Emmanuel Berthier, and Hervé Andrieu. "Parameterization of the Urban Water Budget with the Submesoscale Soil Model." Journal of Applied Meteorology and Climatology 45, no. 4 (April 1, 2006): 624–48. http://dx.doi.org/10.1175/jam2363.1.
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Abstract This paper presents the hydrological component of the Submesoscale Soil Model, urbanized version (SM2-U). This model is an extension of the rural Interactions between Soil, Biosphere, and Atmosphere (ISBA) soil model to urban surfaces. It considers in detail both rural and urban surfaces. Its purpose is to compute the sensible heat and humidity fluxes at the canopy–atmosphere interface for the computational domain lower boundary condition of atmospheric mesoscale models in order to simulate the urban boundary layer in any weather conditions. Because it computes separately the surface temperature of each land use cover mode while the original model computes a unique temperature for the soil and vegetation system, the new version is first validated for rural grounds by comparison with experimental data from the Hydrological Atmospheric Pilot Experiment-Modélisation du Bilan Hydrique (HAPEX-MOBILHY) and the European Field Experiment in a Desertification Threatened Area (EFEDA). The SM2-U water budget is then evaluated on the experimental data obtained at a suburban site in the Nantes urban area (Rezé, France), both on an annual scale and for two stormy events. SM2-U evaluates correctly the water flow measured in the drainage network (DN) at the annual scale and for the summer storm. As for the winter storm, when the soil is saturated, the simulation shows that water infiltration from the soil to the DN must be taken care of to evaluate correctly the DN flow. Yet, the addition of this soil water infiltration to the DN does not make any difference in the simulated surface fluxes that are the model outputs for simulating the urban boundary layer. Urban hydrological parameters are shown to largely influence the available water on artificial surfaces for evaporation and to influence less the evapotranspiration from natural surfaces. The influence of the water budget and surface structure on the suburban site local climatology is demonstrated.
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Huang, Yi-Hsuan, Chun-Chieh Wu, and Michael T. Montgomery. "Concentric Eyewall Formation in Typhoon Sinlaku (2008). Part III: Horizontal Momentum Budget Analyses." Journal of the Atmospheric Sciences 75, no. 10 (October 2018): 3541–63. http://dx.doi.org/10.1175/jas-d-18-0037.1.
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This is a follow-up work to two prior studies examining secondary eyewall formation (SEF) in Typhoon Sinlaku (2008). This study shows that, in the SEF region, the majority of the elevated winds are supergradient. About two-thirds of the rapid increase in tangential wind tendencies immediately prior to SEF are attributed to agradient wind tendencies. This suggests the importance of nonlinear, unbalanced dynamical processes in SEF in addition to the classical axisymmetric balanced response to forcings of heating and momentum. In the SEF region, analyses show two distinct responsible processes for the increasing azimuthal tangential wind in two vertical intervals. Within the boundary inflow layer, the competing effect between the mean radial influx of absolute vorticity and deceleration caused by surface friction and subgrid diffusion yields a secondary maximum of positive tendency. Analyses further demonstrate the major impact of the mean radial influx of absolute vorticity on SEF. Above the boundary inflow layer, the vertical advection acts to vertically extend the tangential wind jet via the lofting of the enhanced tangential momentum farther upward. The roles of the nonlinear unbalanced dynamics in these two processes are discussed in this paper. From a Lagrangian perspective, the persistently increasing agradient force outweighs the frictional loss, effectively decelerating boundary layer inflowing air across the SEF region. This explains the sharpening of the radial gradient of boundary layer inflow, which is shown to be responsible for the buildup of a zone with concentrated boundary layer convergence. The previously proposed unbalanced dynamical pathway to SEF is elaborated upon and supported by the current results and discussion.
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Koseki, Shunya, and Masahiro Watanabe. "Atmospheric Boundary Layer Response to Mesoscale SST Anomalies in the Kuroshio Extension." Journal of Climate 23, no. 10 (May 15, 2010): 2492–507. http://dx.doi.org/10.1175/2009jcli2915.1.
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Abstract The atmospheric boundary layer (ABL) response to mesoscale eddies in sea surface temperature (SST) in the Kuroshio Extension was investigated using a high-resolution (T213L30) atmospheric general circulation model. A control run was performed first by integrating the model for 40 days, driven by the satellite-derived, eddy-resolving SST during January 2006. The spatial pattern of surface wind anomalies—that is, a deviation from large-scale winds—reveals a positive correlation with the spatial pattern of mesoscale SST anomalies. The momentum budget analysis of the anomalous zonal wind was performed to investigate the formation of the ABL response. The most dominant term was the pressure gradient force; the advection term was comparable but in the opposite sense. Vertical mixing acts to weaken the anomalous zonal wind near the surface; however, the downward (upward) vertical turbulent flux anomalies were dominant near the ABL top over the warm (cold) SST anomalies, suggesting that the vertical mixing mechanism is effective. The role of the vertical mixing was further examined by a sensitivity experiment in which the turbulent diffusion coefficient for momentum was spatially smoothed. While the pressure gradient force and the advection terms were almost unchanged in the momentum budgets, the deceleration due to turbulence was enhanced because of the absence of the momentum input from the free atmosphere. The result is a reduction in the amplitude of the surface zonal wind anomalies to approximately half in the sensitivity experiment.
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Wang, Liang, and Dan Li. "Modulation of the urban boundary‐layer heat budget by a heatwave." Quarterly Journal of the Royal Meteorological Society 145, no. 722 (April 10, 2019): 1814–31. http://dx.doi.org/10.1002/qj.3526.
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Steeneveld, G. J., B. J. H. van de Wiel, and A. A. M. Holtslag. "Modeling the Evolution of the Atmospheric Boundary Layer Coupled to the Land Surface for Three Contrasting Nights in CASES-99." Journal of the Atmospheric Sciences 63, no. 3 (March 1, 2006): 920–35. http://dx.doi.org/10.1175/jas3654.1.
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Abstract The modeling and prediction of the stable boundary layer over land is a persistent, problematic feature in weather, climate, and air quality topics. Here, the performance of a state-of-the-art single-column boundary layer model is evaluated with observations from the 1999 Cooperative Atmosphere–Surface Exchange Study (CASES-99) field experiment. Very high model resolution in the atmosphere and the soil is utilized to represent three different stable boundary layer archetypes, namely, a fully turbulent night, an intermittently turbulent night, and a radiative night with hardly any turbulence (all at clear skies). Each archetype represents a different class of atmospheric stability. In the current model, the atmosphere is fully coupled to a vegetation layer and the underlying soil. In addition, stability functions (local scaling) are utilized based on in situ observations. Overall it is found that the vertical structure, the surface fluxes (apart from the intermittent character) and the surface temperature in the stable boundary layer can be satisfactorily modeled for a broad stability range (at a local scale) with the current understanding of the physics of the stable boundary layer. This can also be achieved by the use of a rather detailed coupling between the atmosphere and the underlying soil and vegetation, together with high resolution in both the atmosphere and the soil. This is especially true for the very stable nights, when longwave radiative cooling is dominant. Both model outcome and observations show that in the latter case the soil heat flux is a dominant term of the surface energy budget.
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Denzler, Basil, Christian Bogdal, Cyrill Kern, Anna Tobler, Jing Huo, and Konrad Hungerbühler. "Urban source term estimation for mercury using a boundary-layer budget method." Atmospheric Chemistry and Physics 19, no. 6 (March 25, 2019): 3821–31. http://dx.doi.org/10.5194/acp-19-3821-2019.
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Abstract. Mercury is a heavy metal of particular concern due to its adverse effects on human health and the environment. Recognizing this problem, the UN Minamata Convention on Mercury was recently adopted, where signatory countries agreed to reduce anthropogenic mercury emissions. To evaluate the effectiveness of the convention, quantitative knowledge on mercury emissions is crucial. So far, bottom-up approaches have successfully been applied to quantify mercury emission – especially for point sources. Distributed sources make up a large share of the emission; however, they are still poorly characterized. Here, we present a top-down approach to estimate mercury emissions based on atmospheric measurements in the city of Zurich, Switzerland. While monitoring the atmospheric mercury concentrations during inversion periods in Zurich, we were able to relate the concentration increase to the mercury emission strength of the city using a box model. By means of this boundary-layer budget approach, we succeeded in narrowing down the emissions of Zurich to range between 41±8 kg a−1 (upper bound) and 24±8 kg a−1 (lower bound). Thereby, we could quantify emissions from mixed, diffuse and point-like sources and derive an annual mercury per capita emission of 0.06 to 0.10 g a−1. The approach presented here has the potential to support authorities in setting up inventories and to validate emission estimations derived from the commonly applied bottom-up approaches. Furthermore, our method is applicable to other compounds and to a wide range of cities or other areas, where sources or sinks for mercury and other atmospheric pollutants are presumed.
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Dupont, Sylvain, and Patrice G. Mestayer. "Parameterization of the Urban Energy Budget with the Submesoscale Soil Model." Journal of Applied Meteorology and Climatology 45, no. 12 (December 1, 2006): 1744–65. http://dx.doi.org/10.1175/jam2417.1.
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Abstract The thermal component of the Soil Model for Submesoscales, Urbanized Version (SM2-U), is described. SM2-U is an extension on a physical basis of the rural Interactions between Soil, Biosphere, and Atmosphere (ISBA) soil model to urban areas. It evaluates the turbulent energy, moisture, and radiative fluxes at the urban canopy–atmosphere interface to provide lower boundary conditions of high-resolution mesoscale models. Unlike previous urban canopy schemes, SM2-U integrates in a simple way the physical processes inside the urban canopy: the building wall influence is integrated in the pavement temperature equation, allowing the model to compute directly the energy budget of street canyons. The SM2-U model is evaluated on the Marseille, France, city-center energy-budget components measured during the field experiments to constrain models of atmospheric pollution and transport of emissions [Expérience sur Site pour Contraindre les Modèles de Pollution Atmosphérique et de Transport d’Emissions (ESCOMPTE)] urban boundary layer (UBL) campaign (June–July 2001). The observed behavior of net radiation and heat fluxes is reproduced by SM2-U with a high level of quality, demonstrating that the influence of building walls may be well modeled by modifying the pavement temperature equation. A sensitivity analysis shows that the accurate account of wall area and the parameterization of both the fast response of artificial materials to environmental forcing variations and their heat storage capacity are essential for mesoscale simulations of the urban boundary layer; they are probably more important than accurate but complex computation of radiative trapping (effective albedo and emissivity)
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Mironov, Dmitrii V., and Peter P. Sullivan. "Second-Moment Budgets and Mixing Intensity in the Stably Stratified Atmospheric Boundary Layer over Thermally Heterogeneous Surfaces." Journal of the Atmospheric Sciences 73, no. 1 (December 31, 2015): 449–64. http://dx.doi.org/10.1175/jas-d-15-0075.1.
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Abstract The effect of horizontal temperature heterogeneity of the underlying surface on the turbulence structure and mixing intensity in the stably stratified boundary layer (SBL) is analyzed using large-eddy simulation (LES). Idealized LESs of flows driven by fixed winds and homogeneous and heterogeneous surface temperatures are compared. The LES data are used to compute statistical moments, to estimate budgets of the turbulence kinetic energy (TKE), of the temperature variance and of the temperature flux, and to assess the relative importance of various terms in maintaining the budgets. Unlike most previous studies, the LES-based second-moment budgets are estimated with due regard for the subgrid-scale contributions. The SBL over a heterogeneous surface is more turbulent with larger variances (and TKE), is better vertically mixed, and is deeper compared to its homogeneous counterpart. The most striking difference between the cases is exhibited in the temperature variance and its budget. Because of surface heterogeneity, the turbulent transport term (divergence of the third-order moment) not only redistributes the temperature variance vertically but is a net gain. The increase in the temperature variance near the heterogeneous surface explains the reduced magnitude of the downward buoyancy flux and the ensuing increase in TKE that leads to more vigorous mixing. Analysis of the temperature flux budget shows that the transport term contributes to net production/destruction. Importantly, the role of the third-order transport cannot be elucidated if the budgets are computed based solely on resolved-scale fields. Implications for modeling (parameterizing) the SBL over thermally heterogeneous surfaces are discussed.
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Stieger, J., I. Bamberger, N. Buchmann, and W. Eugster. "Validation of farm-scale methane emissions using nocturnal boundary layer budgets." Atmospheric Chemistry and Physics Discussions 15, no. 15 (August 12, 2015): 21765–802. http://dx.doi.org/10.5194/acpd-15-21765-2015.
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Abstract. This study provides the first experimental validation of Swiss agricultural methane emission estimates at the farm scale. We measured CH4 concentrations at a Swiss farmstead during two intensive field campaigns in August 2011 and July 2012 to (1) quantify the source strength of livestock methane emissions using a tethered balloon system, and (2) to validate inventory emission estimates via nocturnal boundary layer (NBL) budgets. Field measurements were performed at a distance of 150 m from the nearest farm buildings with a tethered balloon system in combination with gradient measurements at eight heights on a 10 m tower to better resolve the near-surface concentrations. Vertical profiles of air temperature, relative humidity, CH4 concentration, wind speed and wind direction showed that the NBL was strongly influenced by local transport processes and by the valley wind system. Methane concentrations showed a pronounced time course, with highest concentrations in the second half of the night. NBL budget flux estimates were obtained via a time–space kriging approach. Main uncertainties of NBL budget flux estimates were associated with instationary atmospheric conditions and the estimate of the inversion height zi (top of volume integration). The mean NBL budget fluxes of 1.60 ± 0.31 μg CH4 m-2 s-1 (1.40 ± 0.50 and 1.66 ± 0.20 μg CH4 m-2 s-1 in 2011 and 2012, respectively) were in good agreement with local inventory estimates based on current livestock number and default emission factors, with 1.29 ± 0.47 and 1.74 ± 0.63 μg CH4 m-2 s-1 for 2011 and 2012, respectively. This indicates that emission factors used for the national inventory reports are adequate, and we conclude that the NBL budget approach is a useful tool to validate emission inventory estimates.
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Albrecht, Bruce, Ming Fang, and Virendra Ghate. "Exploring Stratocumulus Cloud-Top Entrainment Processes and Parameterizations by Using Doppler Cloud Radar Observations." Journal of the Atmospheric Sciences 73, no. 2 (February 1, 2016): 729–42. http://dx.doi.org/10.1175/jas-d-15-0147.1.
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Abstract Observations made at the Atmospheric Radiation Measurement (ARM) Program’s Southern Great Plains (SGP) site during uniform nonprecipitating stratocumulus cloud conditions for a 14-h period are used to examine cloud-top entrainment processes and parameterizations. The observations from a vertically pointing Doppler cloud radar provide estimates of vertical velocity variance and energy dissipation rate (EDR) terms in the parameterized turbulent kinetic energy (TKE) budget of the entrainment zone. Hourly averages of the vertical velocity variance term in the TKE entrainment formulation correlated strongly (r = 0.72) with the dissipation rate term in the entrainment zone, with an increased correlation (r = 0.92) when accounting for the nighttime decoupling of the boundary layer. Independent estimates of entrainment rates were obtained from an inversion-height budget using the local time derivative and horizontal advection of cloud-top height together with large-scale vertical velocity at the boundary layer inversion from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis model. The mean entrainment rate from the inversion-height budget during the 14-h period was 0.74 ± 0.15 cm s−1 and was used to calculate bulk coefficients for entrainment parameterizations based on convective velocity scale w* and TKE budgets of the entrainment zone. The hourly values of entrainment rates calculated using these coefficients exhibited good agreement with those calculated from the inversion-height budget associated with substantial changes in surface buoyancy production and cloud-top radiative cooling. The results indicate a strong potential for making entrainment rate estimates directly from radar vertical velocity variance and the EDR measurements.
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Raatikainen, Tomi, Marje Prank, Jaakko Ahola, Harri Kokkola, Juha Tonttila, and Sami Romakkaniemi. "The effect of marine ice-nucleating particles on mixed-phase clouds." Atmospheric Chemistry and Physics 22, no. 6 (March 21, 2022): 3763–78. http://dx.doi.org/10.5194/acp-22-3763-2022.
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Abstract. Shallow marine mixed-phase clouds are important for the Earth's radiative balance, but modelling their formation and dynamics is challenging. These clouds depend on boundary layer turbulence and cloud top radiative cooling, which is related to the cloud phase. The fraction of frozen droplets depends on the availability of suitable ice-nucleating particles (INPs), which initiate droplet freezing. While mineral dust is the dominating INP type in most regions, high-latitude boundary layer clouds can be dependent on local marine INP emissions, which are often related to biogenic sources including phytoplankton. Here we use high resolution large eddy simulations to examine the potential effects of marine emissions on boundary layer INP concentrations and their effects on clouds. Surface emissions have a direct effect on INP concentration in a typical well-mixed boundary layer whereas a steep inversion can block the import of background INPs from the free troposphere. The importance of the marine source depends on the background INP concentration, so that marine INP emissions become more important with lower background INP concentrations. For the INP budget it is also important to account for INP recycling. Finally, with the high-resolution model we show how ice nucleation hotspots and high INP concentrations are focused on updraught regions. Our results show that marine INP emissions contribute directly to the boundary layer INP budget and therefore have an influence on mixed-phase clouds.
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Conley, S. A., I. Faloona, G. H. Miller, D. H. Lenschow, B. Blomquist, and A. Bandy. "Closing the dimethyl sulfide budget in the tropical marine boundary layer during the Pacific Atmospheric Sulfur Experiment." Atmospheric Chemistry and Physics 9, no. 22 (November 17, 2009): 8745–56. http://dx.doi.org/10.5194/acp-9-8745-2009.
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Abstract. Fourteen research flights were conducted with the National Center for Atmospheric Research (NCAR) C-130 near Christmas Island (2° N, 157° W) during the summer of 2007 as part of the Pacific Atmospheric Sulfur Experiment (PASE). In order to tightly constrain the scalar budget of DMS, vertical eddy fluxes were measured at various levels in the marine boundary layer (MBL) from ~30 m to the top of the mixed layer (~500 m) providing improved accuracy of the flux divergence calculation in the DMS budget. The observed mean mole fraction of DMS in the MBL exhibited the well-known diurnal cycle, ranging from 50–95 pptv in the daytime to 90–110 pptv at night. Contributions from horizontal advection are included using a multivariate regression of all DMS flight data within the MBL to estimate the mean gradients and trends. With this technique we can use the residual term in the DMS budget as an estimate of overall photochemical oxidation. Error analysis of the various terms in the DMS budget indicate that chemical losses acting on time scales of up to 110 h can be inferred with this technique. On average, photochemistry accounted for ~7.4 ppt hr −1 loss rate for the seven daytime flights, with an estimated error of 0.6 ppt hr−1. The loss rate due to expected OH oxidation is sufficient to explain the net DMS destruction without invoking the action of additional oxidants (e.g., reactive halogens.) The observed ocean flux of DMS averaged 3.1 (±1.5) μmol m−2 d−1, and generally decreased throughout the sunlit hours. Over the entire mission, the horizontal advection contribution to the overall budget was merely -0.1 ppt hr−1, indicating a mean atmospheric DMS gradient nearly perpendicular to the east-southeasterly trade winds and the chlorophyll gradient in the equatorial upwelling ocean. Nonetheless, horizontal advection was a significant term in the budget of any given flight, ranging from −1.2 to 2.5 ppt hr−1 , indicating a patchy and variable surface seawater DMS distribution, and thus needs to be accounted for in budget studies.
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Hristov, Tihomir, and Jesus Ruiz-Plancarte. "Dynamic Balances in a Wavy Boundary Layer." Journal of Physical Oceanography 44, no. 12 (November 26, 2014): 3185–94. http://dx.doi.org/10.1175/jpo-d-13-0209.1.
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Abstract The authors analyze the influence of waves on the budgets of momentum flux and kinetic energy in the atmospheric flow over sea surface waves and use the findings to reinterpret the results from the earlier empirical studies on the subject. This analysis employs the framework of wave–mean flow interaction and experimental data collected recently over the open ocean. From a minimal set of plausible assumptions, limited to small-slope waves and uncorrelated turbulent and wave-induced motions in the wind, this study demonstrates that the budgets apply separately to the turbulent and the wave-induced flows. The explicit forms of the wave-supported fluxes of momentum and kinetic energy favor wave spectra ∝ ω−β, 4 ≤ β ≤ 5 for wind–wave equilibrium. These explicit forms also show that in common conditions at heights above one significant wave height from the unperturbed surface, the wave-supported fluxes are a small fraction of the total, of the order of 5%. The wave influence on the kinetic energy budget and on the shape of the wind profile is therefore also small at these heights and thus difficult to identify experimentally next to influences from nonstationarity or horizontal inhomogeneity. Consequently, the predictions of Monin–Obukhov phenomenology show little sensitivity to wave effects. This makes the phenomenology as valid over the ocean as it is over land, but a poor instrument for studying wind–wave interaction. Describing the wind–wave interaction through the dynamics and statistics of the wave-induced motion remains a viable and productive alternative.
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Medeiros, Brian, David L. Williamson, Cécile Hannay, and Jerry G. Olson. "Southeast Pacific Stratocumulus in the Community Atmosphere Model." Journal of Climate 25, no. 18 (April 11, 2012): 6175–92. http://dx.doi.org/10.1175/jcli-d-11-00503.1.
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Abstract Forecasts of October 2006 are used to investigate southeast Pacific stratocumulus in the Community Atmosphere Model, versions 4 and 5 (CAM4 and CAM5). Both models quickly develop biases similar to their climatic biases, suggesting that parameterized physics are the root of the climate errors. An extensive cloud deck is produced in CAM4, but the cloud structure is unrealistic because the boundary layer is too shallow and moist. The boundary layer structure is improved in CAM5, but during the daytime the boundary layer decouples from the cloud layer, causing the cloud layer to break up and transition toward a more trade wind cumulus structure in the afternoon. The cloud liquid water budget shows how different parameterizations contribute to maintaining these different expressions of stratocumulus. Sensitivity experiments help elucidate the origins of the errors. The importance of the diurnal cycle of these clouds for climate simulations is emphasized.
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Saunois, M., C. E. Reeves, C. Mari, J. G. Murphy, D. J. Stewart, G. P. Mills, D. E. Oram, and R. M. Purvis. "Ozone budget in the West African lower troposphere during the AMMA (African Monsoon Multidisciplinary Analysis) campaign." Atmospheric Chemistry and Physics Discussions 9, no. 2 (March 16, 2009): 6979–7032. http://dx.doi.org/10.5194/acpd-9-6979-2009.
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Abstract. A bi-dimensional latitudinal-vertical meterological model coupled with O3-NOx-VOC chemistry is used to reproduce the distribution of ozone and precursors in the boundary layer over West Africa during the African Monsoon Multidisciplinary Analysis (AMMA) campaign as observed on board the Facility for Airborne Atmospheric Measurements (FAAM) BAe 146 Atmospheric Research Aircraft. The model reproduces the increase of ozone mixing ratios in the boundary layer observed between the forested region south of 13° N and the Sahelian area northward. Sensitivity and budget analysis reveals that the intertropical convergence zone is a moderate source of O3 rich-air in the boundary layer due to convective downdrafts. Dry deposition drives the ozone minimum over the vegetated area. The combination of high NOx emissions from soil north of 13° N and northward advection by the monsoon flux of VOC-enriched air masses contributes to the ozone maximum simulated at higher latitudes. Simulated OH exhibit a well marked latitudinal gradient with minimum concentrations over the vegetated region where the reactions with biogenic compounds predominate. The model underestimates the observed OH mixing ratios, however this model discrepancy has slight effect on ozone budget and does not alter the conclusions.
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Blay-Carreras, E., D. Pino, J. Vilà-Guerau de Arellano, A. van de Boer, O. De Coster, C. Darbieu, O. Hartogensis, F. Lohou, M. Lothon, and H. Pietersen. "Role of the residual layer and large-scale subsidence on the development and evolution of the convective boundary layer." Atmospheric Chemistry and Physics 14, no. 9 (May 7, 2014): 4515–30. http://dx.doi.org/10.5194/acp-14-4515-2014.
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Abstract. Observations, mixed-layer theory and the Dutch Large-Eddy Simulation model (DALES) are used to analyze the dynamics of the boundary layer during an intensive operational period (1 July 2011) of the Boundary Layer Late Afternoon and Sunset Turbulence campaign. Continuous measurements made by remote sensing and in situ instruments in combination with radio soundings, and measurements done by remotely piloted aircraft systems and two manned aircrafts probed the vertical structure and the temporal evolution of the boundary layer during the campaign. The initial vertical profiles of potential temperature, specific humidity and wind, and the temporal evolution of the surface heat and moisture fluxes prescribed in the models runs are inspired by some of these observations. The research focuses on the role played by the residual layer during the morning transition and by the large-scale subsidence on the evolution of the boundary layer. By using DALES, we show the importance of the dynamics of the boundary layer during the previous night in the development of the boundary layer at the morning. DALES numerical experiments including the residual layer are capable of modeling the observed sudden increase of the boundary-layer depth during the morning transition and the subsequent evolution of the boundary layer. These simulations show a large increase of the entrainment buoyancy flux when the residual layer is incorporated into the mixed layer. We also examine how the inclusion of the residual layer above a shallow convective boundary layer modifies the turbulent kinetic energy budget. Large-scale subsidence mainly acts when the boundary layer is fully developed, and, for the studied day, it is necessary to be considered to reproduce the afternoon observations. Finally, we also investigate how carbon dioxide (CO2) mixing ratio stored the previous night in the residual layer plays a fundamental role in the evolution of the CO2 mixing ratio during the following day.
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de Szoeke, Simon P., Christopher S. Bretherton, Nicholas A. Bond, Meghan F. Cronin, and Bruce M. Morley. "EPIC 95°W Observations of the Eastern Pacific Atmospheric Boundary Layer from the Cold Tongue to the ITCZ." Journal of the Atmospheric Sciences 62, no. 2 (February 1, 2005): 426–42. http://dx.doi.org/10.1175/jas-3381.1.
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Abstract The atmospheric boundary layer (ABL) along 95°W in the eastern equatorial Pacific during boreal autumn is described using data from the East Pacific Investigation of Climate (EPIC) 2001, with an emphasis on the evolution of the thermodynamic ABL properties from the cold tongue to the cold-advection region north of the sea surface temperature (SST) front. Surface sensible and latent heat fluxes and wind stresses between 1°S and 12°N are calculated from data from eight NCAR C-130 research aircraft flights and from Tropical Atmosphere Ocean (TAO) buoys. Reduced surface wind speed and a 10 m s−1 jet at a height of 500 m are found over the equatorial cold tongue, demonstrating the dependence of the surface wind speed on surface stability. The ABL exhibits a maximum in cloud cover on the north (downwind) side of the warm SST front, at 1°–3°N. Turbulent mixing driven by both surface buoyancy flux and radiative cooling at the cloud tops plays a significant role in maintaining the depth and structure of the ABL. The ABL heat budget between the equator and 3°N is balanced by comparable contributions from advective cooling, radiative cooling, surface warming, and entrainment warming. Entrainment drying is a weak contributor to the moisture budget, relative to dry advection and surface evaporation. Both the heat and moisture budgets are consistent with a rapid entrainment rate, 12 ± 2 mm s−1, deduced from the observed rise of the inversion with latitude between 0° and 4°N.
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Zhang, Yang, and Peter H. Stone. "Baroclinic Adjustment in an Atmosphere–Ocean Thermally Coupled Model: The Role of the Boundary Layer Processes." Journal of the Atmospheric Sciences 68, no. 11 (November 1, 2011): 2710–30. http://dx.doi.org/10.1175/jas-d-11-078.1.
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Abstract Baroclinic eddy equilibration and the roles of different boundary layer processes in limiting the baroclinic adjustment are studied using an atmosphere–ocean thermally coupled model. Boundary layer processes not only affect the dynamical constraint of the midlatitude baroclinic eddy equilibration but also are important components in the underlying surface energy budget. The authors' study shows that baroclinic eddies, with the strong mixing of the surface air temperature, compete against the fast boundary layer thermal damping and enhance the meridional variation of surface sensible heat flux, acting to reduce the meridional gradient of the surface temperature. Nevertheless, the requirement of the surface energy balance indicates that strong surface baroclinicity is always maintained in response to the meridionally varying solar radiation. With the strong surface baroclinicity and the boundary layer processes, the homogenized potential vorticity (PV) suggested in the baroclinic adjustment are never observed near the surface or in the boundary layer. Although different boundary layer processes affect baroclinic eddy equilibration differently with more dynamical feedbacks and time scales included in the coupled system, their influence in limiting the PV homogenization is more uniform compared with the previous uncoupled runs. The boundary layer PV structure is more determined by the strength of the boundary layer damping than the surface baroclinicity. Stronger boundary layer processes always prevent the lower-level PV homogenization more efficiently. Above the boundary layer, a relatively robust PV structure with homogenized PV around 600–800 hPa is obtained in all of the simulations. The detailed mechanisms through which different boundary layer processes affect the equilibration of the coupled system are discussed in this study.
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Holdsworth, Amber M., and Adam H. Monahan. "Turbulent Collapse and Recovery in the Stable Boundary Layer Using an Idealized Model of Pressure-Driven Flow with a Surface Energy Budget." Journal of the Atmospheric Sciences 76, no. 5 (May 1, 2019): 1307–27. http://dx.doi.org/10.1175/jas-d-18-0312.1.
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Abstract The evolution of the stable boundary layer is simulated using an idealized single-column model of pressure-driven flow coupled to a surface energy budget. Several commonly used parameterizations of turbulence are examined. The agreement between the simulated wind and temperature profiles and tower observations from the Cabauw tower is generally good given the simplicity of the model. The collapse and recovery of turbulence is explored in the presence of a large-scale pressure gradient, but excluding transient submesoscale atmospheric forcings such as internal waves and density-driven currents. The sensitivity tests presented here clarify the role of both rotation and the surface energy budget in the collapse and recovery of turbulence for the pressure-driven dry stable boundary layer (SBL). Conditions of stability are affected strongly by the geostrophic winds, the cloud cover, and the thermal conductivity of the surface. Inertial oscillations and the subsurface temperature have a weaker influence. Particularly noteworthy is the relationship between SBL regime and the relative importance of the terms in the surface energy budget.
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Kalmus, Peter, Matthew Lebsock, and João Teixeira. "Observational Boundary Layer Energy and Water Budgets of the Stratocumulus-to-Cumulus Transition." Journal of Climate 27, no. 24 (December 10, 2014): 9155–70. http://dx.doi.org/10.1175/jcli-d-14-00242.1.
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Abstract The authors estimate summer mean boundary layer water and energy budgets along a northeast Pacific transect from 35° to 15°N, which includes the transition from marine stratocumulus to trade cumulus clouds. Observational data is used from three A-Train satellites, Aqua, CloudSat, and the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO); data derived from GPS signals intercepted by microsatellites of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC); and the container-ship-based Marine Atmospheric Radiation Measurement Program (ARM) Global Energy and Water Cycle Experiment Cloud System Study/Working Group on Numerical Experimentation (GCSS/WGNE) Pacific Cross-Section Intercomparison (GPCI) Investigation of Clouds (MAGIC) campaign. These are unique satellite and shipborne observations providing the first global-scale observations of light precipitation, new vertically resolved radiation budget products derived from the active sensors, and well-sampled radiosonde data near the transect. In addition to the observations, the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim) fields are utilized to estimate the budgets. Both budgets approach within 3 W m−2 averaged along the transect, although uncertainty estimates from the study are much larger than this residual. A mean entrainment rate along the transect of mm s−1 is also estimated. A gradual transition is observed in the climatological mean from the stratocumulus regime to the cumulus regime characterized by an increase in boundary layer height, latent heat flux, rain, and the horizontal advection of dry air and a decrease in entrainment of warm dry air.
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Ponnulakshmi, V. K., D. K. Singh, V. Mukund, K. R. Sreenivas, and G. Subramanian. "Hypercooling in the Atmospheric Boundary Layer: Beyond Broadband Emissivity Schemes." Journal of the Atmospheric Sciences 70, no. 1 (January 1, 2013): 278–83. http://dx.doi.org/10.1175/jas-d-12-095.1.
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Abstract In an accompanying paper by Ponnulakshmi et al., the prevailing flux emissivity scheme for nonblack surfaces was shown to include an erroneous reflected flux term. The error leads to a spurious cooling within the opaque bands; an expression for the correct broadband-reflected flux was given that eliminated this spurious cooling contribution. Herein, it is shown that the error is generic in nature, and is relevant to any frequency-parameterized radiation scheme applied to nonblack surfaces; such schemes are typically used in longwave radiation budget calculations. The correct reflected flux, previously developed within the framework of a broadband emissivity scheme in Ponnulakshmi et al., is generalized here so as to be applicable to any frequency-parameterized radiation model. The error is illustrated by comparing the bandwise fluxes, obtained using the prevailing and correct narrowband formulations, for a model (tropical) atmosphere. The flux discrepancy is the smallest for opaque bands within which the participating medium emits like a blackbody, and it is largest in frequency intervals where the medium is nearly transparent.
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Rotunno, Richard, and George H. Bryan. "Effects of Parameterized Diffusion on Simulated Hurricanes." Journal of the Atmospheric Sciences 69, no. 7 (July 1, 2012): 2284–99. http://dx.doi.org/10.1175/jas-d-11-0204.1.
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Abstract In this study the authors analyze and interpret the effects of parameterized diffusion on the nearly steady axisymmetric numerical simulations of hurricanes presented in a recent study. In that study it was concluded that horizontal diffusion was the most important control factor for the maximum simulated hurricane intensity. Through budget analysis it is shown here that horizontal diffusion is a major contributor to the angular momentum budget in the boundary layer of the numerically simulated storms. Moreover, a new scale analysis recognizing the anisotropic nature of the parameterized model diffusion shows why the horizontal diffusion plays such a dominant role. A simple analytical model is developed that captures the essence of the effect. The role of vertical diffusion in the boundary layer in the aforementioned numerical simulations is more closely examined here. It is shown that the boundary layer in these simulations is consistent with known analytical solutions in that boundary layer depth increases and the amount of “overshoot” (maximum wind in excess of the gradient wind) decreases with increasing vertical diffusion. However, the maximum wind itself depends mainly on horizontal diffusion and is relatively insensitive to vertical diffusion; the overshoot variation with vertical viscosity mainly comes from changes in the gradient wind with vertical viscosity. The present considerations of parameterized diffusion allow a new contribution to the dialog in the literature on the meaning and interpretation of the Emanuel potential intensity theory.
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Pino, D., J. Vilà-Guerau de Arellano, W. Peters, J. Schröter, C. C. van Heerwaarden, and M. C. Krol. "A conceptual framework to quantify the influence of convective boundary layer development on carbon dioxide mixing ratios." Atmospheric Chemistry and Physics 12, no. 6 (March 26, 2012): 2969–85. http://dx.doi.org/10.5194/acp-12-2969-2012.
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Abstract. Interpretation of observed diurnal carbon dioxide (CO2) mixing ratios near the surface requires knowledge of the local dynamics of the planetary boundary layer. In this paper, we study the relationship between the boundary layer dynamics and the CO2 budget in convective conditions through a newly derived set of analytical equations. From these equations, we are able to quantify how uncertainties in boundary layer dynamical variables or in the morning CO2 distribution in the mixed-layer or in the free atmosphere (FA) influence the bulk CO2 mixing ratio. We find that the largest uncertainty incurred on the mid-day CO2 mixing ratio comes from the prescribed early morning CO2 mixing ratios in the stable boundary layer, and in the free atmosphere. Errors in these values influence CO2 mixing ratios inversely proportional to the boundary layer depth (h), just like uncertainties in the assumed initial boundary layer depth and surface CO2 flux. The influence of uncertainties in the boundary layer depth itself is one order of magnitude smaller. If we "invert" the problem and calculate CO2 surface exchange from observed or simulated CO2 mixing ratios, the sensitivities to errors in boundary layer dynamics also invert: they become linearly proportional to the boundary layer depth. We demonstrate these relations for a typical well characterized situation at the Cabauw site in The Netherlands, and conclude that knowledge of the temperature and carbon dioxide profiles of the atmosphere in the early morning are of vital importance to correctly interpret observed CO2 mixing ratios during midday.
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Braun, Scott A. "High-Resolution Simulation of Hurricane Bonnie (1998). Part II: Water Budget." Journal of the Atmospheric Sciences 63, no. 1 (January 1, 2006): 43–64. http://dx.doi.org/10.1175/jas3609.1.
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Abstract The fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) is used to simulate Hurricane Bonnie at high resolution (2-km spacing) in order to examine budgets of water vapor, cloud condensate, and precipitation. Virtually all budget terms are derived directly from the model (except for the effects of storm motion). The water vapor budget reveals that a majority of the condensation in the eyewall occurs in convective hot towers, while outside of the eyewall most of the condensation occurs in weaker updrafts, indicative of a larger role of stratiform precipitation processes. The ocean source of water vapor in the eyewall region is only a very small fraction of that transported inward in the boundary layer inflow or that condensed in the updrafts. In contrast, in the outer regions, the ocean vapor source is larger owing to the larger area, counters the drying effect of low-level subsidence, and enhances the moisture transported in toward the eyewall. In this mature storm, cloud condensate is consumed as rapidly as it is produced. Cloud water peaks at the top of the boundary layer and within the melting layer, where cooling from melting enhances condensation. Unlike in squall lines, in the hurricane, very little condensate produced in the eyewall convection is transported outward into the surrounding precipitation area. Most of the mass ejected outward is likely in the form of small snow particles that seed the outer regions and enhance in situ stratiform precipitation development through additional growth by vapor deposition and aggregation. This study also examines artificial source terms for cloud and precipitation mass associated with setting to zero negative mixing ratios that arise from numerical advection errors. Although small at any given point and time, the cumulative effect of these terms contributes an amount of mass equivalent to 13% of the total condensation and 15%–20% of the precipitation. Thus, these terms must be accounted for to balance the model budgets, and the results suggest the need for improved model numerics.
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Kuhn, M. "Micro-Meteorological Conditions for Snow Melt." Journal of Glaciology 33, no. 113 (1987): 24–26. http://dx.doi.org/10.1017/s002214300000530x.
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AbstractThe energy budget of a snow or ice surface is determined by atmospheric variables like solar and atmospheric long-wave radiation, air temperature, and humidity; the transfer of energy from the free atmosphere to the surface depends on the stability of the atmospheric boundary layer, where vertical profiles of wind speed and temperature determine stability, and on surface conditions like surface temperature (and thus surface humidity), roughness, and albedo.This paper investigates the conditions exactly at the onset or the end of melting using air temperature, humidity, and as the radiation term the sum of global and reflected short-wave plus downward long-wave radiation. For the turbulent exchange in the boundary layer, examples are computed with a transfer coefficient of 18.5 W m−2K−1which corresponds to the average over the ablation period on an Alpine glacier. Ways to estimate the transfer coefficient for various degrees of stability are indicated in the Appendix.It appears from such calculations that snow may melt at air temperatures as low as –10°C and may stay frozen at +10°C.
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Kuhn, M. "Micro-Meteorological Conditions for Snow Melt." Journal of Glaciology 33, no. 113 (1987): 24–26. http://dx.doi.org/10.3189/s002214300000530x.
Full textAbstract:
AbstractThe energy budget of a snow or ice surface is determined by atmospheric variables like solar and atmospheric long-wave radiation, air temperature, and humidity; the transfer of energy from the free atmosphere to the surface depends on the stability of the atmospheric boundary layer, where vertical profiles of wind speed and temperature determine stability, and on surface conditions like surface temperature (and thus surface humidity), roughness, and albedo.This paper investigates the conditions exactly at the onset or the end of melting using air temperature, humidity, and as the radiation term the sum of global and reflected short-wave plus downward long-wave radiation. For the turbulent exchange in the boundary layer, examples are computed with a transfer coefficient of 18.5 W m−2 K−1 which corresponds to the average over the ablation period on an Alpine glacier. Ways to estimate the transfer coefficient for various degrees of stability are indicated in the Appendix.It appears from such calculations that snow may melt at air temperatures as low as –10°C and may stay frozen at +10°C.
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Allaerts, Dries, and Johan Meyers. "Boundary-layer development and gravity waves in conventionally neutral wind farms." Journal of Fluid Mechanics 814 (February 6, 2017): 95–130. http://dx.doi.org/10.1017/jfm.2017.11.
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While neutral atmospheric boundary layers are rare over land, they occur frequently over sea. In these cases they are almost always of the conventionally neutral type, in which the neutral boundary layer is capped by a strong inversion layer and a stably stratified atmosphere aloft. In the current study, we use large-eddy simulations (LES) to investigate the interaction between a large wind farm that has a fetch of 15 km and a conventionally neutral boundary layer (CNBL) in typical offshore conditions. At the domain inlet, we consider three different equilibrium CNBLs with heights of approximately 300 m, 500 m and 1000 m that are generated in a separate precursor LES. We find that the height of the inflow boundary layer has a significant impact on the wind farm flow development. First of all, above the farm, an internal boundary layer develops that interacts downwind with the capping inversion for the two lowest CNBL cases. Secondly, the upward displacement of the boundary layer by flow deceleration in the wind farm excites gravity waves in the inversion layer and the free atmosphere above. For the lower CNBL cases, these waves induce significant pressure gradients in the farm (both favourable and unfavourable depending on location and case). A detailed energy budget analysis in the turbine region shows that energy extracted by the wind turbines comes both from flow deceleration and from vertical turbulent entrainment. Though turbulent transport dominates near the end of the farm, flow deceleration remains significant, i.e. up to 35 % of the turbulent flux for the lowest CNBL case. In fact, while the turbulent fluxes are fully developed after eight turbine rows, the mean flow does not reach a stationary regime. A further energy budget analysis over the rest of the CNBL reveals that all energy available at turbine level comes from upwind kinetic energy in the boundary layer. In the lower CNBL cases, the pressure field induced by gravity waves plays an important role in redistributing this energy throughout the farm. Overall, in all cases entrainment at the capping inversion is negligible, and also the work done by the mean background pressure gradient, arising from the geostrophic balance in the free atmosphere, is small.
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Conley, S. A., I. Faloona, G. H. Miller, B. Blomquist, D. Lenschow, and A. Bandy. "Closing the Dimethyl Sulfide Budget in the Tropical Marine Boundary Layer during the Pacific Atmospheric Sulfur Experiment." Atmospheric Chemistry and Physics Discussions 9, no. 4 (August 14, 2009): 17265–96. http://dx.doi.org/10.5194/acpd-9-17265-2009.
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Abstract. Fourteen research flights were conducted with the National Center for Atmospheric Research (NCAR) C-130 near Christmas Island (2° N, 157° W) during the summer of 2007 as part of the Pacific Atmospheric Sulfur Experiment (PASE). In order to tightly constrain the scalar budget of DMS, fluxes were measured at various levels in the marine boundary layer (MBL) from near the surface (30 m) to the top of the mixed layer (500 m) providing greater accuracy of the flux divergence calculation in the DMS budget. The observed mean mole fraction of DMS in the MBL exhibited the well known diurnal cycle, ranging from 50 pptv in the daytime to 110 pptv at night. Contributions from horizontal advection are included using a multivariate regression of all DMS flight data from within the MBL to estimate the mean gradients and trends. With this technique we consider the residual term in the DMS budget as an estimate of overall photochemical oxidation. Error analysis of the various terms in the DMS budget indicate that chemical losses acting on time scales of up to 110 h can be inferred with this technique. On average, photochemistry accounted for 7.3 ppt hr−1 loss rate for the seven daytime flights, with an estimated error of 0.6 ppt/hr. The loss rate due to expected OH oxidation is sufficient to explain the net DMS destruction without invoking the action of additional oxidants (e.g. reactive halogens.) The observed ocean flux of DMS averaged 3.1 (±1.5)μmol m−2 d−1, and generally decreased throughout the sunlit hours. The average entrainment flux at the top of the MBL was 2.5 μmol m−2 d−1; therefore the flux divergence term in the budget equation only contributed an average increase of 1.3 ppt hr−1 to the mean MBL mole fraction. Over the entire mission, the horizontal advection contribution to the overall budget was 0.2 ppt hr−1, indicating a mean atmospheric DMS gradient nearly perpendicular to the east-southeasterly trade winds and the chlorophyll gradient in the equatorial upwelling ocean. Nonetheless, horizontal advection was a significant term in the budget of any given flight, ranging from −1.5 to 2.3 ppt hr−1, indicating a patchy and random seawater DMS distribution, and thus needs to be accounted for in budget studies.
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Babić, Karmen, and Mathias W. Rotach. "Turbulence kinetic energy budget in the stable boundary layer over a heterogeneous surface." Quarterly Journal of the Royal Meteorological Society 144, no. 713 (April 2018): 1045–62. http://dx.doi.org/10.1002/qj.3274.
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Paulot, F., D. K. Henze, and P. O. Wennberg. "Impact of the isoprene photochemical cascade on tropical ozone." Atmospheric Chemistry and Physics 12, no. 3 (February 2, 2012): 1307–25. http://dx.doi.org/10.5194/acp-12-1307-2012.
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Abstract. Tropical tropospheric ozone affects Earth's radiative forcing and the oxidative capacity of the atmosphere. Considerable work has been devoted to the study of the processes controlling its budget. Yet, large discrepancies between simulated and observed tropical tropospheric ozone remain. Here, we characterize some of the mechanisms by which the photochemistry of isoprene impacts the budget of tropical ozone. At the regional scale, we use forward sensitivity simulation to explore the sensitivity to the representation of isoprene nitrates. We find that isoprene nitrates can account for up to 70% of the local NOx = NO+NO2 sink. The resulting modulation of ozone can be well characterized by their net modulation of NOx. We use adjoint sensitivity simulations to demonstrate that the oxidation of isoprene can affect ozone outside of continental regions through the transport of NOx over near-shore regions (e.g., South Atlantic) and the oxidation of isoprene outside of the boundary layer far from its emissions regions. The latter mechanism is promoted by the simulated low boundary-layer oxidative conditions. In our simulation, ~20% of the isoprene is oxidized above the boundary layer in the tropics. Changes in the interplay between regional and global effect are discussed in light of the forecasted increase in anthropogenic emissions in tropical regions.
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Chandra, Arunchandra S., Pavlos Kollias, Scott E. Giangrande, and Stephen A. Klein. "Long-Term Observations of the Convective Boundary Layer Using Insect Radar Returns at the SGP ARM Climate Research Facility." Journal of Climate 23, no. 21 (November 1, 2010): 5699–714. http://dx.doi.org/10.1175/2010jcli3395.1.
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Abstract A long-term study of the turbulent structure of the convective boundary layer (CBL) at the U.S. Department of Energy Atmospheric Radiation Measurement Program (ARM) Southern Great Plains (SGP) Climate Research Facility is presented. Doppler velocity measurements from insects occupying the lowest 2 km of the boundary layer during summer months are used to map the vertical velocity component in the CBL. The observations cover four summer periods (2004–08) and are classified into cloudy and clear boundary layer conditions. Profiles of vertical velocity variance, skewness, and mass flux are estimated to study the daytime evolution of the convective boundary layer during these conditions. A conditional sampling method is applied to the original Doppler velocity dataset to extract coherent vertical velocity structures and to examine plume dimension and contribution to the turbulent transport. Overall, the derived turbulent statistics are consistent with previous aircraft and lidar observations. The observations provide unique insight into the daytime evolution of the convective boundary layer and the role of increased cloudiness in the turbulent budget of the subcloud layer. Coherent structures (plumes–thermals) are found to be responsible for more than 80% of the total turbulent transport resolved by the cloud radar system. The extended dataset is suitable for evaluating boundary layer parameterizations and testing large-eddy simulations (LESs) for a variety of surface and cloud conditions.
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Gorski, Galen, Courtenay Strong, Stephen P. Good, Ryan Bares, James R. Ehleringer, and Gabriel J. Bowen. "Vapor hydrogen and oxygen isotopes reflect water of combustion in the urban atmosphere." Proceedings of the National Academy of Sciences 112, no. 11 (March 2, 2015): 3247–52. http://dx.doi.org/10.1073/pnas.1424728112.
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Anthropogenic modification of the water cycle involves a diversity of processes, many of which have been studied intensively using models and observations. Effective tools for measuring the contribution and fate of combustion-derived water vapor in the atmosphere are lacking, however, and this flux has received relatively little attention. We provide theoretical estimates and a first set of measurements demonstrating that water of combustion is characterized by a distinctive combination of H and O isotope ratios. We show that during periods of relatively low humidity and/or atmospheric stagnation, this isotopic signature can be used to quantify the concentration of water of combustion in the atmospheric boundary layer over Salt Lake City. Combustion-derived vapor concentrations vary between periods of atmospheric stratification and mixing, both on multiday and diurnal timescales, and respond over periods of hours to variations in surface emissions. Our estimates suggest that up to 13% of the boundary layer vapor during the period of study was derived from combustion sources, and both the temporal pattern and magnitude of this contribution were closely reproduced by an independent atmospheric model forced with a fossil fuel emissions data product. Our findings suggest potential for water vapor isotope ratio measurements to be used in conjunction with other tracers to refine the apportionment of urban emissions, and imply that water vapor emissions associated with combustion may be a significant component of the water budget of the urban boundary layer, with potential implications for urban climate, ecohydrology, and photochemistry.