Kliknij ten link, aby zobaczyć inne rodzaje publikacji na ten temat: MLT circulation.
Artykuły w czasopismach na temat „MLT circulation”
Utwórz poprawne odniesienie w stylach APA, MLA, Chicago, Harvard i wielu innych
Sprawdź 50 najlepszych artykułów w czasopismach naukowych na temat „MLT circulation”.
Przycisk „Dodaj do bibliografii” jest dostępny obok każdej pracy w bibliografii. Użyj go – a my automatycznie utworzymy odniesienie bibliograficzne do wybranej pracy w stylu cytowania, którego potrzebujesz: APA, MLA, Harvard, Chicago, Vancouver itp.
Możesz również pobrać pełny tekst publikacji naukowej w formacie „.pdf” i przeczytać adnotację do pracy online, jeśli odpowiednie parametry są dostępne w metadanych.
Przeglądaj artykuły w czasopismach z różnych dziedzin i twórz odpowiednie bibliografie.
1
Griffith, Matthew J., David R. Jackson, Daniel J. Griffin i Chris J. Budd. "Stable extension of the unified model into the mesosphere and lower thermosphere". Journal of Space Weather and Space Climate 10 (2020): 19. http://dx.doi.org/10.1051/swsc/2020018.
Pełny tekst źródłaStreszczenie:
A coupled Sun-to-Earth model is the goal for accurate forecasting of space weather. A key component of such a model is a whole atmosphere model – a general circulation model extending from the ground into the upper atmosphere – since it is now known that the lower atmosphere also drives variability and space weather in the upper atmosphere, in addition to solar variability. This objective motivates the stable extension of The Met Office’s Unified Model (UM) into the Mesosphere and Lower Thermosphere (MLT), acting as a first step towards a whole atmosphere model. At the time of performing this research, radiation and chemistry schemes that are appropriate for use in the MLT had not yet been implemented. Furthermore, attempts to run the model with existing parameterizations and a raised upper boundary led to an unstable model with inaccurate solutions. Here, this instability is examined and narrowed down to the model’s radiation scheme – its assumption of Local Thermodynamic Equilibrium (LTE) is broken in the MLT. We subsequently address this issue by relaxation to a climatological temperature profile in this region. This provides a stable extended UM which can be used as a developmental tool for further examination of the model performance. The standard vertical resolution used in the UM above 70 km is too coarse (approx. 5 km) to represent waves that are important for MLT circulation. We build on the success of the nudging implementation by testing the model at an improved vertical resolution. Initial attempts to address this problem with a 3 km vertical resolution and a 100 km lid were successful, but on increasing the resolution to 1.5 km the model becomes unstable due to large horizontal and vertical wind velocities. Increasing the vertical damping coefficient, which damps vertical velocities near the upper boundary, allows a successful year long climatology to be produced with these model settings. With the goal of a whole atmosphere model we also experiment with an increased upper boundary height. Increasing the upper model boundary to 120 and 135 km also leads to stable simulations. However, a 3 km resolution must be used and it is necessary to further increase the vertical damping coefficient. This is highly promising initial work to raise the UM into the MLT, and paves the way for the development of a whole atmosphere model.
2
Mbatha, N., V. Sivakumar, S. B. Malinga, H. Bencherif i S. R. Pillay. "Study on the impact of sudden stratosphere warming in the upper mesosphere-lower thermosphere regions using satellite and HF radar measurements". Atmospheric Chemistry and Physics Discussions 9, nr 6 (2.11.2009): 23051–72. http://dx.doi.org/10.5194/acpd-9-23051-2009.
Pełny tekst źródłaStreszczenie:
Abstract. The occurrence of sudden stratospheric warming (SSW) excites disturbances in the mesosphere-lower thermospheric (MLT) wind and temperature. Here, we have examined the high frequency (HF) radar wind data from the South African National Antarctic Expedition, SANAE (72° S, 3° W), a radar which is part of the Super Dual Auroral Radar Network (SuperDARN). Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on board the Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics (TIMED) satellite temperature data and National Centre for Environmental Prediction (NCEP) temperature and wind data were use to investigate the dynamical effects of the unprecedented September 2002 SSW in the Antarctica stratosphere and MLT. The mean zonal wind (from SANAE HF radar) at the MLT shows reversal in approximately 7 days before the reversal at 10 hPa (from NCEP). This indicates that there was a downwards propagation of circulation disturbance. Westerly zonal winds dominate the winter MLT, but during the 2002 winter there were many periods of westward winds observed compared to other years. The dynamic spectrums of both meridional and zonal winds show presence of planetary waves (of ~14-day period) before the occurrence of the SSW. The SABER vertical temperature profiles indicated the cooling of the MLT region before the SSW event.
3
Mbatha, N., V. Sivakumar, S. B. Malinga, H. Bencherif i S. R. Pillay. "Study on the impact of sudden stratosphere warming in the upper mesosphere-lower thermosphere regions using satellite and HF radar measurements". Atmospheric Chemistry and Physics 10, nr 7 (12.04.2010): 3397–404. http://dx.doi.org/10.5194/acp-10-3397-2010.
Pełny tekst źródłaStreszczenie:
Abstract. The occurrence of a sudden stratospheric warming (SSW) excites disturbances in the mesosphere-lower thermospheric (MLT) wind and temperature. Here, we have examined the high frequency (HF) radar wind data from the South African National Antarctic Expedition, SANAE (72° S, 3° W), a radar which is part of the Super Dual Auroral Radar Network (SuperDARN). Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on board the Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics (TIMED) satellite temperature data and National Centre for Environmental Prediction (NCEP) temperature and wind data are used to investigate the dynamical effects of the unprecedented September 2002 SSW in the Antarctica stratosphere and MLT. The mean zonal wind (from SANAE HF radar) at the MLT shows reversal approximately 7 days before the reversal at 10 hPa (from NCEP). This indicates that there was a downwards propagation of circulation disturbance. Westerly zonal winds dominate the winter MLT, but during the 2002 winter there are many periods of westward winds observed compared to other years. The normalised power spectrums of both meridional and zonal winds show presence of planetary waves (of ~14-day period) before the occurrence of the SSW. The SABER vertical temperature profiles indicated the cooling of the MLT region before the SSW event.
4
Griffith, Matthew J., Shaun M. Dempsey, David R. Jackson, Tracy Moffat-Griffin i Nicholas J. Mitchell. "Winds and tides of the Extended Unified Model in the mesosphere and lower thermosphere validated with meteor radar observations". Annales Geophysicae 39, nr 3 (10.06.2021): 487–514. http://dx.doi.org/10.5194/angeo-39-487-2021.
Pełny tekst źródłaStreszczenie:
Abstract. The mesosphere and lower thermosphere (MLT) is a critical region that must be accurately reproduced in general circulation models (GCMs) that aim to include the coupling between the lower and middle atmosphere and the thermosphere. An accurate representation of the MLT is thus important for improved climate modelling and the development of a whole atmosphere model. This is because the atmospheric waves at these heights are particularly large, and so the energy and momentum they carry is an important driver of climatological phenomena through the whole atmosphere, affecting terrestrial and space weather. The Extended Unified Model (ExUM) is the recently developed version of the Met Office's Unified Model which has been extended to model the MLT. The capability of the ExUM to model atmospheric winds and tides in the MLT is currently unknown. Here, we present the first study of winds and tides from the ExUM. We make a comparison against meteor radar observations of winds and tides from 2006 between 80 and 100 km over two radar stations – Rothera (68∘ S, 68∘ W) and Ascension Island (8∘ S, 14∘ W). These locations are chosen to study tides in two very different tidal regimes – the equatorial regime, where the diurnal (24 h) tide dominates, and the polar regime, where the semi-diurnal (12 h) tide dominates. The results of this study illustrate that the ExUM is capable of reproducing atmospheric winds and tides that capture many of the key characteristics seen in meteor radar observations, such as zonal and meridional wind maxima and minima, the increase in tidal amplitude with increasing height, and the decrease in tidal phase with increasing height. In particular, in the equatorial regime some essential characteristics of the background winds, tidal amplitudes and tidal phases are well captured but with significant differences in detail. In the polar regime, the difference is more pronounced. The ExUM zonal background winds in austral winter are primarily westward rather than eastward, and in austral summer they are larger than observed above 90 km. The ExUM tidal amplitudes here are in general consistent with observed values, but they are also larger than observed values above 90 km in austral summer. The tidal phases are generally well replicated in this regime. We propose that the bias in background winds in the polar regime is a consequence of the lack of in situ gravity wave generation to generate eastward fluxes in the MLT. The results of this study indicate that the ExUM has a good natural capability for modelling atmospheric winds and tides in the MLT but that there is room for improvement in the model physics in this region. This highlights the need for modifications to the physical parameterization schemes used in the model in this region – such as the non-orographic spectral gravity wave scheme – to improve aspects such as polar circulation. To this end, we make specific recommendations of changes that can be implemented to improve the accuracy of the ExUM in the MLT.
5
Wei, Guanchun, Jianyong Lu, Wenbin Wang, Yufeng Tian, Jingyuan Li, Shiping Xiong, Meng Sun i in. "Temperature Variations in the Mesosphere and Lower Thermosphere during Geomagnetic Storms with Disparate Durations at High Latitudes". Universe 9, nr 2 (5.02.2023): 86. http://dx.doi.org/10.3390/universe9020086.
Pełny tekst źródłaStreszczenie:
Using the temperature data observed from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), we investigate the response of the mesosphere and lower thermosphere (MLT) to two medium geomagnetic storms with disparate durations, on 20 April 2018 and 10 April 2022. The high-latitude MLT temperature increase in the Southern hemisphere can reach 40 K during April 2018 geomagnetic storm with a longer duration (Kp values greater than 4 for 15 h), while the temperature variations are less than 10 K for the April 2022 event (Kp values greater than 4 for 6 h). To investigate the different temperature responses to disparate geomagnetic storm durations and understand what physical process results in this difference, we simulated the two events using the thermosphere ionosphere mesosphere electrodynamics general circulation model (TIMEGCM). The simulations show that more particles and energy input in longer-duration geomagnetic storms produce larger ion drag force and pressure gradient force at ~130 km, and then the enhanced two forces cause faster horizontal wind, leading to larger horizontal divergence. Subsequently, the stronger downward vertical wind is transported to the MLT region (below 110 km) and ultimately makes greater temperature increases through adiabatic heating/cooling and vertical advection. Therefore, the effects of the storm’s duration on the MLT temperature are also important.
6
Long, Chi, Tao Yu, Yang-Yi Sun, Xiangxiang Yan, Jian Zhang, Na Yang, Jin Wang, Chunliang Xia, Yu Liang i Hailun Ye. "Atmospheric Gravity Wave Derived from the Neutral Wind with 5-Minute Resolution Routinely Retrieved by the Meteor Radar at Mohe". Remote Sensing 15, nr 2 (4.01.2023): 296. http://dx.doi.org/10.3390/rs15020296.
Pełny tekst źródłaStreszczenie:
Atmospheric gravity waves (GWs) in the mesosphere-lower thermosphere (MLT) are crucial for the understanding of general circulation. However, their dynamical characteristics are hardly retrieved due to the difficulty in the high-resolution observation of wind. Therefore, this paper uses eight years (2013–2020) of meteor radar measurements in the MLT region at Mohe station (53.5, 122.3), China, to retrieve high-temporal-resolution mesospheric wind data and further evaluate the temporal variation of GW kinetic energy. As the detected meteor trails exceed 6, the wind velocity is recalculated using the least square algorithm method, significantly increasing the temporal resolution of wind from 1 h up to 5 min. This resolution is sufficiently high for the investigation of GW kinetic energy, which exhibits a high spatial-temporal variability. For instance, it is enhanced in the winter season during the period of 0200–1400 UT and in the spring season during the period of 0800–1300 UT. The similarity between the climatological characteristics of GWs in MLT and the seasonal variation of GW total energy in the troposphere, determined from high-resolution radiosondes near to Mohe station, suggests that the meteorology in the lower atmosphere could be an important source of GWs in the MLT region.
7
Jacobi, Christoph, Tatiana Ermakova, Daniel Mewes i Alexander I. Pogoreltsev. "El Niño influence on the mesosphere/lower thermosphere circulation at midlatitudes as seen by a VHF meteor radar at Collm (51.3 ° N, 13 ° E)". Advances in Radio Science 15 (21.09.2017): 199–206. http://dx.doi.org/10.5194/ars-15-199-2017.
Pełny tekst źródłaStreszczenie:
Abstract. Mesosphere/lower thermosphere (MLT) zonal winds continuously measured by a VHF meteor radar at Collm, Germany (51.3° N, 13.0° E) in the height range 82 – 97 km from 2004 to date are analyzed with respect to the signature of El Niño. The comparison of Niño3 equatorial SST index and MLT wind time series shows that in January and especially in February zonal winds are positively correlated with the Niño3 index. We note a delay of about one month of the MLT zonal wind effect with respect to equatorial sea surface temperature variability. The signal is strong for the upper altitudes (above 90 km) accessible to the radar observations, but weakens with decreasing height. This reflects the fact that during El Niño years the westerly winter middle atmosphere wind jet is weaker, and this is also the case with the easterly lower thermospheric jet. Owing to the reversal of the absolute El Niño signal from negative to positive with altitude, at the height of the maximum meteor flux, which is around 90 km, the El Niño signal is weak. The experimental results can be qualitatively reproduced by numerical experiments using a mechanistic global circulation model with prescribed tropospheric temperatures and latent heat release for El Niño and La Niña conditions.
8
Tang, Qiong, Haiyang Sun, Zhitao Du, Jiaqi Zhao, Yi Liu, Zhengyu Zhao i Xueshang Feng. "Unusual Enhancement of Midlatitude Sporadic-E Layers in Response to a Minor Geomagnetic Storm". Atmosphere 13, nr 5 (16.05.2022): 816. http://dx.doi.org/10.3390/atmos13050816.
Pełny tekst źródłaStreszczenie:
This study investigates the variations of middle and low latitude sporadic-E (Es) layers in response to a geomagnetic storm. Es layers are observed by five ionosondes located in the Eastern Asian sector. The critical frequencies of Es layers (foEs) at six stations increased in sequence from high latitude stations to low latitude stations after IMF/Bz turning southward. Lomb–Scargle analysis shows the amplification of semidiurnal oscillation amplitude in the vertical height of Es layers during geomagnetic disturbance. Modeling results of the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) show the enhancement of the wind field in the mesosphere and the lower thermosphere (MLT) region. Our study provides evidence that the enhanced wind field in the MLT region during the storm period could result in the enhancement of Es layers at middle and low latitude.
9
Yoshikawa, M., i S. Miyahara. "Zonal mean meridional circulation in the low to middle latitude of MLT region: A numerical simulation by a general circulation model". Advances in Space Research 32, nr 5 (wrzesień 2003): 709–17. http://dx.doi.org/10.1016/s0273-1177(03)00405-8.
Pełny tekst źródła
10
Dawe, Jordan T., i Lu Anne Thompson. "PDO-Related Heat and Temperature Budget Changes in a Model of the North Pacific". Journal of Climate 20, nr 10 (15.05.2007): 2092–108. http://dx.doi.org/10.1175/jcli4229.1.
Pełny tekst źródłaStreszczenie:
Abstract Heat and temperature budget changes in a ⅓° model of the North Pacific driven by an idealized Pacific decadal oscillation (PDO) atmospheric forcing are diagnosed to determine the roles of atmospheric heat flux and ocean dynamics in upper-ocean heat content and mixed layer temperature (MLT) changes. Changes in MLT and heat content during the transition between negative and positive PDOs are driven primarily by atmospheric heat fluxes, with contributions from ageostrophic advection and entrainment. Once the new PDO state is established, atmospheric heat flux in the central North Pacific works to mitigate the MLT change while vertical entrainment and ageostrophic advection act to enhance it. Upper-ocean heat content is affected in a similar matter, except that vertical processes are not important in the heat budget balance. At the same time, changes in wind stress curl cause the subtropical gyre to spin up and the subpolar gyre boundary to migrate southward. These circulation changes cause a large increase in the geostrophic advective heat flux in the Kuroshio region. This increase results in more heat flux to the atmosphere, demonstrating an active role for ocean dynamics in the upper-ocean heat budget. Eddy heat flux divergence along the Kuroshio Extension doubles after the transition, due to stronger eddy activity related to increased Kuroshio transport.
11
Kako, Shin’ichiro, i Masahisa Kubota. "Numerical Study on the Variability of Mixed Layer Temperature in the North Pacific". Journal of Physical Oceanography 39, nr 3 (1.03.2009): 737–52. http://dx.doi.org/10.1175/2008jpo3979.1.
Pełny tekst źródłaStreszczenie:
Abstract Physical processes important for the interannual variability in mixed layer temperature (MLT) in the North Pacific have been examined by using a three-dimensional bulk mixed layer model. This model was forced by the momentum, heat, and freshwater flux data derived from the NCEP–NCAR reanalysis and geostrophic flow data included in Japanese Ocean Flux datasets with Use of Remote Sensing Observations. The interannual variation in MLT was hindcasted over the course of 11 years from January 1993 to December 2003. The interannual variation in the modeled MLT favorably agreed with that of the available in situ and satellite sea surface temperature (SST) observational data. This agreement depended crucially on whether horizontal heat advection was considered a part of the model dynamics. Although both atmospheric and oceanic processes were required to explain the observed interannual MLT variability, the physical process most important for determining this variability was likely to differ year by year. For example, in the Kuroshio Extension region, it was found that the positive temperature tendency peak in 1997 was attributed to the positive surface thermal forcing, while the temperature tendency in 1998 and 1999 continued to increase in spite of the negative surface thermal forcing. Thus, the abnormal heat loss from the ocean to the atmosphere (hence, the atmospheric circulation change) in 1998–99 was considered to be excited by the ocean dynamics related to the warmer SST. Likewise, it was found that the rapid decrease in SST during 2001–03 was mainly caused by the effect of lateral flux.
12
Egito, Fabio, Hisao Takahashi i Yasunobu Miyoshi. "Effects of the planetary waves on the MLT airglow". Annales Geophysicae 35, nr 5 (31.08.2017): 1023–32. http://dx.doi.org/10.5194/angeo-35-1023-2017.
Pełny tekst źródłaStreszczenie:
Abstract. The planetary-wave-induced airglow variability in the mesosphere and lower thermosphere (MLT) is investigated using simulations with the general circulation model (GCM) of Kyushu University. The model capabilities enable us to simulate the MLT OI557.7 nm, O2b(0–1), and OH(6–2) emissions. The simulations were performed for the lower-boundary meteorological conditions of 2005. The spectral analysis reveals that at middle latitudes, oscillations of the emission rates with the period of 2–20 days appear throughout the year. The 2-day oscillations are prominent in the summer and the 5-, 10-, and 16-day oscillations dominate from the autumn to spring equinoxes. The maximal amplitude of the variations induced by the planetary waves was 34 % in OI557.7 nm, 17 % in O2b(0–1), and 8 % in OH(6–2). The results were compared to those observed in the middle latitudes. The GCM simulations also enabled us to investigate vertical transport processes and their effects on the emission layers. The vertical transport of atomic oxygen exhibits similar periodic variations to those observed in the emission layers induced by the planetary waves. The results also show that the vertical advection of atomic oxygen due to the wave motion is an important factor in the signatures of the planetary waves in the emission rates.
13
Griffith, Matthew J., i Nicholas J. Mitchell. "Analysis of migrating and non-migrating tides of the Extended Unified Model in the mesosphere and lower thermosphere". Annales Geophysicae 40, nr 3 (1.06.2022): 327–58. http://dx.doi.org/10.5194/angeo-40-327-2022.
Pełny tekst źródłaStreszczenie:
Abstract. Atmospheric tides play a key role in coupling the lower, middle, and upper atmosphere/ionosphere. The tides reach large amplitudes in the mesosphere and lower thermosphere (MLT), where they can have significant fluxes of energy and momentum, and so strongly influence the coupling and dynamics. The tides must therefore be accurately represented in general circulation models (GCMs) that seek to model the coupling of atmospheric layers and impacts on the ionosphere. The tides consist of both migrating (sun-following) and non-migrating (not sun-following) components, both of which have important influences on the atmosphere. The Extended Unified Model (ExUM) is a recently developed version of the Met Office's GCM (the Unified Model) which has been extended to include the MLT. Here, we present the first in-depth analysis of migrating and non-migrating components in the ExUM. We show that the ExUM produces both non-migrating and migrating tides in the MLT of significant amplitude across a rich spectrum of spatial and temporal components. The dominant non-migrating components in the MLT are found to be DE3, DW2, and DW3 in the diurnal tide and S0, SW1, and SW3 in the semidiurnal tide. These components in the model can have monthly mean amplitudes at a height of 95 km as large as 35 m s−1/10 K. All the non-migrating components exhibit a strong seasonal variability in amplitude, and a significant short-term variability is evident. Both the migrating and non-migrating components exhibit notable variation with latitude. For example, the temperature and wind diurnal tides maximise at low latitudes and the semidiurnal tides include maxima at high latitudes. A comparison against published satellite and ground-based observations shows generally good agreement in latitudinal tidal structure, with more differences in seasonal tidal structure. Our results demonstrate the capability of the ExUM for modelling atmospheric migrating and non-migrating tides, and this lays the foundation for its future development into a whole atmosphere model. To this end, we make specific recommendations on further developments which would improve the capability of the model.
14
Hindley, Neil P., Nicholas J. Mitchell, Neil Cobbett, Anne K. Smith, Dave C. Fritts, Diego Janches, Corwin J. Wright i Tracy Moffat-Griffin. "Radar observations of winds, waves and tides in the mesosphere and lower thermosphere over South Georgia island (54° S, 36° W) and comparison with WACCM simulations". Atmospheric Chemistry and Physics 22, nr 14 (22.07.2022): 9435–59. http://dx.doi.org/10.5194/acp-22-9435-2022.
Pełny tekst źródłaStreszczenie:
Abstract. The mesosphere and lower thermosphere (MLT) is a dynamic layer of the earth's atmosphere. This region marks the interface at which neutral atmosphere dynamics begin to influence the upper atmosphere and ionosphere. However, our understanding of this region and our ability to accurately simulate it in global circulation models (GCMs) is limited by a lack of observations, especially in remote locations. To this end, a meteor radar was deployed from 2016 to 2020 on the remote mountainous island of South Georgia (54∘ S, 36∘ W) in the Southern Ocean. In this study we use these new measurements to characterise the fundamental dynamics of the MLT above South Georgia including large-scale winds, solar tides, planetary waves (PWs), and mesoscale gravity waves (GWs). We first present an improved method for time–height localisation of radar wind measurements and characterise the large-scale MLT winds. We then determine the amplitudes and phases of the diurnal (24 h), semidiurnal (12 h), terdiurnal (8 h), and quardiurnal (6 h) solar tides at this latitude. We find very large amplitudes up to 30 m s−1 for the quasi 2 d PW in summer and, combining our measurements with the meteor SAAMER radar in Argentina, show that the dominant modes of the quasi 5, 10, and 16 d PWs are westward 1 and 2. We investigate and compare wind variance due to both large-scale “resolved” GWs and small-scale “sub-volume” GWs in the MLT and characterise their seasonal cycles. Last, we use our radar observations and satellite temperature observations from the Microwave Limb Sounder to test a climatological simulation of the Whole Atmosphere Community Climate Model (WACCM). We find that WACCM exhibits a summertime mesopause near 80 km altitude that is around 10 K warmer and 10 km lower in altitude than observed. Above 95 km altitude, summertime meridional winds in WACCM reverse to poleward, but this not observed in radar observations in this altitude range. More significantly, we find that wintertime zonal winds between 85 to 105 km altitude are eastward up to 40 m s−1 in radar observations, but in WACCM they are westward up to 20 m s−1. We propose that this large discrepancy may be linked to the impacts of secondary GWs (2GWs) on the residual circulation, which are not included in most global models, including WACCM. These radar measurements can therefore provide vital constraints that can guide the development of GCMs as they extend upwards into this important region of the atmosphere.
15
Sun, Ruizao, Anmin Duan, Lilan Chen, Yanjie Li, Zhiang Xie i Yu Zhao. "Interannual Variability of the North Pacific Mixed Layer Associated with the Spring Tibetan Plateau Thermal Forcing". Journal of Climate 32, nr 11 (7.05.2019): 3109–30. http://dx.doi.org/10.1175/jcli-d-18-0577.1.
Pełny tekst źródłaStreszczenie:
Abstract By using multisourced data and two sets of sensitivity runs from the coupled general circulation model CESM1.2.0, we investigated the effects of the spring [March, April, and May (MAM)] surface sensible heating over the Tibetan Plateau (SHTP) on the interannual variability of the North Pacific Ocean sea surface temperature (SST) and mixed layer. The results indicated that an above-normal MAM SHTP can generate a Rossby wave downstream and form an anomalous equivalent barotropic anticyclone over the North Pacific, inducing anticyclonic wind stress anomalies. As a result of Ekman transport and Ekman pumping, sea currents converge near 40°N, accompanied by weak downwelling motion. The mixed layer heat budget diagnosis indicates that the net heat fluxes, together with meridional advection anomalies, contributed significantly to changes in the mixed layer temperature (MLT). As a result, the SST anomalies (SSTAs) and MLT anomalies both present a horseshoelike pattern. In addition, the significant warm SSTAs show a maximum in the late spring, but the significant warm MLT anomalies centered under the sea surface (25-m depth) could be sustained until summer, acting like a signal storage for the anomalous spring SHTP. Moreover, the midlatitude ocean–atmosphere interaction provides a positive feedback on the development of the anomalous anticyclone over the North Pacific, since the SSTA pattern could strengthen the oceanic front and induce more active transient eddy activities. The eddy vorticity forcing that is dominant among the total atmospheric forcings tends to produce an equivalent barotropic atmospheric high pressure, which in turn intensifies the initial anomalous anticyclone.
16
Yamashita, K., S. Miyahara, Y. Miyoshi, K. Kawano i J. Ninomiya. "Seasonal variation of non-migrating semidiurnal tide in the polar MLT region in a general circulation model". Journal of Atmospheric and Solar-Terrestrial Physics 64, nr 8-11 (maj 2002): 1083–94. http://dx.doi.org/10.1016/s1364-6826(02)00059-7.
Pełny tekst źródła
17
Yoshikawa, M., i S. Miyahara. "Longitudinal variations of amplitudes of diurnal tides in the MLT region simulated by a general circulation model". Advances in Space Research 32, nr 9 (styczeń 2003): 1751–57. http://dx.doi.org/10.1016/s0273-1177(03)90472-8.
Pełny tekst źródła
18
Chen, Qiuyu, Konstantin Ntokas, Björn Linder, Lukas Krasauskas, Manfred Ern, Peter Preusse, Jörn Ungermann, Erich Becker, Martin Kaufmann i Martin Riese. "Satellite observations of gravity wave momentum flux in the mesosphere and lower thermosphere (MLT): feasibility and requirements". Atmospheric Measurement Techniques 15, nr 23 (8.12.2022): 7071–103. http://dx.doi.org/10.5194/amt-15-7071-2022.
Pełny tekst źródłaStreszczenie:
Abstract. In the recent decade it became evident that we need to revise our picture of how gravity waves (GWs) reach the mesosphere and lower thermosphere (MLT). This has consequences for our understanding not just of the properties of the GWs themselves, but in particular of the global circulation in the MLT. Information on spectral distribution, direction, and zonal mean GW momentum flux is required to test the theoretical and modeling findings. In this study, we propose a constellation of two CubeSats for observing mesoscale GWs in the MLT region by means of temperature limb sounding in order to derive such constraints. Each CubeSat deploys a highly miniaturized spatial heterodyne interferometer (SHI) for the measurement of global oxygen atmospheric band emissions. From these emissions, the 3-D temperature structure can be inferred. We propose obtaining four independent observation tracks by splitting the interferograms in the center and thus gaining two observation tracks for each satellite. We present a feasibility study of this concept based on self-consistent, high-resolution global model data. This yields a full chain of end-to-end (E2E) simulations incorporating (1) orbit simulation, (2) airglow forward modeling, (3) tomographic temperature retrieval, (4) 3-D wave analysis, and (5) GW momentum flux (GWMF) calculation. The simulation performance is evaluated by comparing the retrieved zonal mean GWMF with that computed directly from the model wind data. A major question to be considered in our assessment is the minimum number of tracks required for the derivation of 3-D GW parameters. The main result from our simulations is that the GW polarization relations are still valid in the MLT region and can thus be employed for inferring GWMF from the 3-D temperature distributions. Based on the E2E simulations for gaining zonal mean climatologies of GW momentum flux, we demonstrate that our approach is robust and stable, given a four-track observation geometry and the expected instrument noise under nominal operation conditions. Using phase speed and direction spectra we show also that the properties of individual wave events are recovered when employing four tracks. Finally, we discuss the potential of the proposed observations to address current topics in the GW research. We outline for which investigations ancillary data are required to answer science questions.
19
Sun, Meng, Zheng Li, Jingyuan Li, Jianyong Lu, Chunli Gu, Mengbin Zhu i Yufeng Tian. "Responses of Mesosphere and Lower Thermosphere Temperature to the Geomagnetic Storm on 7–8 September 2017". Universe 8, nr 2 (3.02.2022): 96. http://dx.doi.org/10.3390/universe8020096.
Pełny tekst źródłaStreszczenie:
The variations of neutral temperature in the mesosphere and lower thermosphere (MLT) region, during the 7–8 September 2017 intense geomagnetic storm, are studied using observations by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite. They are also studied using simulations by the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIMEGCM). The neutral temperature data cover the altitudes from 80 km to 110 km between 83° N and 52° S latitude, obtained from both SABER observations and model simulations. The SABER observations reveal that temperature increases (the maximum increase is larger than 35 K at ~108 km) and decreases (the maximum decrease is larger than 20 K at ~105 km) during the geomagnetic storm. The storm effects penetrate down to ~80 km. In observations, temperature variations corresponding to the storm show hemispheric asymmetry. That is, the variations of temperature are more prominent in the northern hemisphere than in the southern hemisphere. Conversely, the TIMEGCM outputs agree with the observations in general but overestimate the temperature increases and underestimate the temperature decreases at high and middle latitudes. Meanwhile, the simulations show stronger temperature decreases and weaker temperature increases than observations at low latitudes. After analyzing the temperature variations, we suggest that vertical winds may play an important role in inducing these significant variations of temperature in the MLT region.
20
Song, Rui, Martin Kaufmann, Manfred Ern, Jörn Ungermann, Guang Liu i Martin Riese. "Three-dimensional tomographic reconstruction of atmospheric gravity waves in the mesosphere and lower thermosphere (MLT)". Atmospheric Measurement Techniques 11, nr 5 (1.06.2018): 3161–75. http://dx.doi.org/10.5194/amt-11-3161-2018.
Pełny tekst źródłaStreszczenie:
Abstract. Gravity waves (GWs) have been intensively studied over recent decades because of their dominant role in the dynamics of the mesosphere and lower thermosphere (MLT). The momentum deposition caused by breaking GWs determines the basic structure and drives the large-scale circulation in the MLT. Satellite observations provide a way to qualify the properties and effects of GWs on a global scale. As GWs can propagate vertically and horizontally in the atmosphere, resolving both horizontal and vertical wavelengths is important for the quantification of a wave. However, this can hardly be achieved by one instrument with a good spatial coverage and resolution. In this paper, we propose a new observation strategy, called “sweep mode”, for a real three-dimensional (3-D) tomographic reconstruction of GWs in the MLT by modifying the observation geometry of conventional limb sounding measurements. It enhances the horizontal resolution that typical limb sounders can achieve, while at the same time retaining the good vertical resolution they have. This observation strategy is simulated for retrieving temperatures from measurements of the rotational structure of the O2 A-band airglow. The idea of this observation strategy is to sweep the line of sight (LOS) of the limb sounder horizontally across the orbital track during the flight. Therefore, two-dimensional (2-D) slices, i.e., vertical planes, that reveal the projection of GWs can be observed in the direction along and across the orbital track, respectively. The 3-D wave vector is then reproduced by combining the projected 2-D wave slices in the two directions. The feasibility of this sweep-mode tomographic retrieval approach is assessed using simulated measurements. It shows that the horizontal resolution in both along- and across-track directions is affected by an adjustable turning angle, which also determines the spatial coverage of this observation mode. The retrieval results can reduce the errors in deducing momentum flux substantially by providing an unbiased estimation of the real horizontal wavelength of a wave.
21
Davis, R. N., Y. W. Chen, S. Miyahara i N. J. Mitchell. "The climatology, propagation and excitation of ultra-fast Kelvin waves as observed by meteor radar, Aura MLS, TRMM and in the Kyushu-GCM". Atmospheric Chemistry and Physics Discussions 11, nr 10 (31.10.2011): 29479–525. http://dx.doi.org/10.5194/acpd-11-29479-2011.
Pełny tekst źródłaStreszczenie:
Abstract. Wind measurements from a meteor radar on Ascension Island (8° S, 14° W) and simultaneous temperature measurements from the Aura MLS instrument are used to characterise ultra-fast Kelvin waves (UFKW) of zonal wavenumber 1 (E1) in the mesosphere and lower thermosphere (MLT) in the years 2005–2010. These observations are compared with some predictions of the Kyushu-general circulation model. Good agreement is found between observations of the UFKW in the winds and temperatures, and also with the properties of the waves in the Kyushu-GCM. UFKW are found at periods between 2.5–4.5 days with amplitudes of up to 40 m s−1 in the zonal winds and 6 K in the temperatures. The average vertical wavelength is found to be 44 km. Amplitudes vary with latitude in a Gaussian manner with the profiles centred over the equator. Dissipation of the waves results in monthly-mean eastward accelerations of 0.2–0.9 m s−1 day−1 at heights around 95 km, with 5-day mean peak values of 4 m s−1 day−1. Largest wave amplitudes and variances are observed over Indonesia and central Africa and may be a result of very strong moist convective heating over those regions. Rainfall data from TRMM are used as a proxy for latent-heat release in an investigation of the excitation of these waves. No strong correlation is found between the occurrence of large-amplitude mesospheric UFKW events and either the magnitude of the equatorial rainfall or the amplitudes of E1 signatures in the rainfall time series, indicating that either other sources or the propagation environment are more important in determining the amplitude of UFKW in the MLT. A strong semiannual variation in wave amplitudes is observed. Intraseasonal oscillations (ISOs) with periods 25–60 days are evident in the zonal background winds, zonal-mean temperature, UFKW amplitudes, UFKW accelerations and the rainfall rate. This suggests that UFKW play a role in carrying the signature of tropospheric ISOs to the MLT region.
22
Davis, R. N., Y. W. Chen, S. Miyahara i N. J. Mitchell. "The climatology, propagation and excitation of ultra-fast Kelvin waves as observed by meteor radar, Aura MLS, TRMM and in the Kyushu-GCM". Atmospheric Chemistry and Physics 12, nr 4 (17.02.2012): 1865–79. http://dx.doi.org/10.5194/acp-12-1865-2012.
Pełny tekst źródłaStreszczenie:
Abstract. Wind measurements from a meteor radar on Ascension Island (8° S, 14° W) and simultaneous temperature measurements from the Aura MLS instrument are used to characterise ultra-fast Kelvin waves (UFKW) of zonal wavenumber 1 (E1) in the mesosphere and lower thermosphere (MLT) in the years 2005–2010. These observations are compared with some predictions of the Kyushu-general circulation model. Good agreement is found between observations of the UFKW in the winds and temperatures, and also with the properties of the waves in the Kyushu-GCM. UFKW are found at periods between 2.5–4.5 days with amplitudes of up to 40 m s−1 in the zonal winds and 6 K in the temperatures. The average vertical wavelength is found to be 44 km. Amplitudes vary with latitude in a Gaussian manner with the maxima centred over the equator. Dissipation of the waves results in monthly-mean eastward accelerations of 0.2–0.9 m s−1 day−1 at heights around 95 km, with 5-day mean peak values of 4 m s−1 day−1. Largest wave amplitudes and variances are observed over Indonesia and central Africa and may be a result of very strong moist convective heating over those regions. Rainfall data from TRMM are used as a proxy for latent-heat release in an investigation of the excitation of these waves. No strong correlation is found between the occurrence of large-amplitude mesospheric UFKW events and either the magnitude of the equatorial rainfall or the amplitudes of E1 signatures in the rainfall time series, indicating that either other sources or the propagation environment are more important in determining the amplitude of UFKW in the MLT. A strong semiannual variation in wave amplitudes is observed. Intraseasonal oscillations (ISOs) with periods 25–60 days are evident in the zonal background winds, zonal-mean temperature, UFKW amplitudes, UFKW accelerations and the rainfall rate. This suggests that UFKW play a role in carrying the signature of tropospheric ISOs to the MLT region.
23
Deng, Zengan, Lian Xie, Ting Yu, Suixiang Shi, Jiye Jin i Kejian Wu. "Numerical Study of the Effects of Wave-Induced Forcing on Dynamics in Ocean Mixed Layer". Advances in Meteorology 2013 (2013): 1–10. http://dx.doi.org/10.1155/2013/365818.
Pełny tekst źródłaStreszczenie:
Numerical experiments using hybrid coordinate ocean model (HYCOM) are designed to quantify the effects of wind wave-induced Coriolis-Stokes forcing (CSF) on mixed layer (ML) dynamics in a global context. CSF calculated by the wave parameters simulated by using the WaveWatch III (WW3) model is introduced as a new driving force for HYCOM. The results show that noticeable influence on ocean circulation in ML can be caused by CSF. Over most of the global oceans the direction of Stokes transport is different from that of the change in current transport caused by CSF. This is not unusual because CSF is normal to Stokes drift. However, the CSF-caused change in current transport and the wave-induced Stokes transport have the same magnitude. The seasonal variabilities of mixed layer temperature (MLT) and mixed layer depth (MLD) caused by CSF are analyzed, and the possible relationship between them is also given.
24
Volz, Ryan, Jorge L. Chau, Philip J. Erickson, Juha P. Vierinen, J. Miguel Urco i Matthias Clahsen. "Four-dimensional mesospheric and lower thermospheric wind fields using Gaussian process regression on multistatic specular meteor radar observations". Atmospheric Measurement Techniques 14, nr 11 (17.11.2021): 7199–219. http://dx.doi.org/10.5194/amt-14-7199-2021.
Pełny tekst źródłaStreszczenie:
Abstract. Mesoscale dynamics in the mesosphere and lower thermosphere (MLT) region have been difficult to study from either ground- or satellite-based observations. For understanding of atmospheric coupling processes, important spatial scales at these altitudes range between tens and hundreds of kilometers in the horizontal plane. To date, this scale size is challenging observationally, so structures are usually parameterized in global circulation models. The advent of multistatic specular meteor radar networks allows exploration of MLT mesoscale dynamics on these scales using an increased number of detections and a diversity of viewing angles inherent to multistatic networks. In this work, we introduce a four-dimensional wind field inversion method that makes use of Gaussian process regression (GPR), which is a nonparametric and Bayesian approach. The method takes measured projected wind velocities and prior distributions of the wind velocity as a function of space and time, specified by the user or estimated from the data, and produces posterior distributions for the wind velocity. Computation of the predictive posterior distribution is performed on sampled points of interest and is not necessarily regularly sampled. The main benefits of the GPR method include this non-gridded sampling, the built-in statistical uncertainty estimates, and the ability to horizontally resolve winds on relatively small scales. The performance of the GPR implementation has been evaluated on Monte Carlo simulations with known distributions using the same spatial and temporal sampling as 1 d of real meteor measurements. Based on the simulation results we find that the GPR implementation is robust, providing wind fields that are statistically unbiased with statistical variances that depend on the geometry and are proportional to the prior velocity variances. A conservative and fast approach can be straightforwardly implemented by employing overestimated prior variances and distances, while a more robust but computationally intensive approach can be implemented by employing training and fitting of model hyperparameters. The latter GPR approach has been applied to a 24 h dataset and shown to compare well to previously used homogeneous and gradient methods. Small-scale features have reasonably low statistical uncertainties, implying geophysical wind field horizontal structures as low as 20–50 km. We suggest that this GPR approach forms a suitable method for MLT regional and weather studies.
25
Vlasov, M. N., i M. C. Kelley. "Estimates of eddy turbulence consistent with seasonal variations of atomic oxygen and its possible role in the seasonal cycle of mesopause temperature". Annales Geophysicae 28, nr 11 (18.11.2010): 2103–10. http://dx.doi.org/10.5194/angeo-28-2103-2010.
Pełny tekst źródłaStreszczenie:
Abstract. According to current understanding, adiabatic cooling and heating induced by the meridional circulation driven by gravity waves is the major process for the cold summer and warm winter polar upper mesosphere. However, our calculations show that the upward/downward motion needed for adiabatic cooling/heating of the summer/winter polar mesopause simultaneously induces a seasonal variation in both the O maximum density and the altitude of the [O] peak that is opposite to the observed variables generalized by the MSISE-90 model. It is usually accepted that eddy turbulence can produce the [O] seasonal variations. Using this approach, we can infer the eddy diffusion coefficient for the different seasons. Taking these results and experimental data on the eddy diffusion coefficient, we consider in detail and estimate the heating and cooling caused by eddy turbulence in the summer and winter polar upper mesosphere. The seasonal variations of these processes are similar to the seasonal variations of the temperature and mesopause. These results lead to the conclusion that heating/cooling by eddy turbulence is an important component in the energy budget and that adiabatic cooling/heating induced by upward/downward motion cannot dominate in the mesopause region. Our study shows that the impact of the dynamic process, induced by gravity waves, on [O] distributions must be included in models of thermal balance in the upper mesosphere and lower thermosphere (MLT) for a consistent description because (a) the [O] distribution is very sensitive to dynamic processes, and (b) atomic oxygen plays a very important role in chemical heating and infrared cooling in the MLT. To our knowledge, this is the first attempt to consider this aspect of the problem.
26
Fox, N. J., M. Lockwood, S. W. H. Cowley, M. P. Freeman, E. Friis-Christensen, D. K. Milling, M. Pinnock i G. D. Reeves. "EISCAT observations of unusual flows in the morning sector associated with weak substorm activity". Annales Geophysicae 12, nr 6 (31.05.1994): 541–53. http://dx.doi.org/10.1007/s00585-994-0541-2.
Pełny tekst źródłaStreszczenie:
Abstract. A discussion is given of plasma flows in the dawn and nightside high-latitude ionospheric regions during substorms occurring on a contracted auroral oval, as observed using the EISCAT CP-4-A experiment. Supporting data from the PACE radar, Greenland magnetometer chain, SAMNET magnetometers and geostationary satellites are compared to the EISCAT observations. On 4 October 1989 a weak substorm with initial expansion phase onset signatures at 0030 UT, resulted in the convection reversal boundary observed by EISCAT (at ~0415 MLT) contracting rapidly poleward, causing a band of elevated ionospheric ion temperatures and a localised plasma density depletion. This polar cap contraction event is shown to be associated with various substorm signatures; Pi2 pulsations at mid-latitudes, magnetic bays in the midnight sector and particle injections at geosynchronous orbit. A similar event was observed on the following day around 0230 UT (~0515 MLT) with the unusual and significant difference that two convection reversals were observed, both contracting poleward. We show that this feature is not an ionospheric signature of two active reconnection neutral lines as predicted by the near-Earth neutral model before the plasmoid is "pinched off", and present two alternative explanations in terms of (1) viscous and lobe circulation cells and (2) polar cap contraction during northward IMF. The voltage associated with the anti-sunward flow between the reversals reaches a maximum of 13 kV during the substorm expansion phase. This suggests it to be associated with the polar cap contraction and caused by the reconnection of open flux in the geomagnetic tail which has mimicked "viscous-like" momentum transfer across the magnetopause.
27
Middleton, H. R., N. J. Mitchell i H. G. Muller. "Mean winds of the mesosphere and lower thermosphere at 52° N in the period 1988–2000". Annales Geophysicae 20, nr 1 (31.01.2002): 81–91. http://dx.doi.org/10.5194/angeo-20-81-2002.
Pełny tekst źródłaStreszczenie:
Abstract. A meteor radar in the UK (near 52° N) has been used to measure the mean winds of the mesosphere/lower-thermosphere (MLT) region over the period 1988–2000. The seasonal course and interannual variability is characterised and comparisons are made with a number of models. Annual mean wind trends were found to be + 0.37 ms-1 yr-1 for the zonal component and + 0.157 ms-1 yr-1 for the meridional component. Seasonal means revealed significant trends in the case of meridional winds in spring ( + 0.38 ms-1 yr-1) and autumn ( + 0.29 ms-1 yr-1), and zonal winds in summer ( + 0.48 ms-1 yr-1) and autumn ( + 0.38 ms-1 yr-1). Significant correlation coefficients, R, between the sunspot number and seasonal mean wind are found in four instances. In the case of the summer zonal winds, R = + 0.732; for the winter meridional winds, R = - 0.677; for the winter zonal winds, R = - 0.472; and for the autumn zonal winds R = + 0.508.Key words. Meteorology and atmospheric dynamics (climatology; general circulation; middle atmospheric dynamics)
28
Sharma, R. D. "Technical Note: On the possibly missing mechanism of 15 μm emission in the mesosphere–lower thermosphere (MLT)". Atmospheric Chemistry and Physics 15, nr 4 (17.02.2015): 1661–67. http://dx.doi.org/10.5194/acp-15-1661-2015.
Pełny tekst źródłaStreszczenie:
Abstract. Accurate knowledge of the rate as well as the mechanism of excitation of the bending mode of CO2 is necessary for reliable modeling of the mesosphere–lower thermosphere (MLT) region of the atmosphere. Assuming the excitation mechanism to be thermal collisions with atomic oxygen, the rate coefficient derived from the observed 15 μm emission by space-based experiments (kATM = 6.0 × 10−12 cm3s−1) differs from the laboratory measurements (kLAB =(1.5-2.5) × 10−12 cm3s−1) by a factor of 2–4. The general circulation models (GCMs) of Earth, Venus, and Mars have chosen to use a median value of kGCM = 3.0 × 10−12 cm3s−1 for this rate coefficient. As a first step to resolve the discrepancies between the three rate coefficients, we attempt to find the source of disagreement between the first two. It is pointed out that a large magnitude of the difference between these two rate coefficients (kx ≡ kATM - kLAB) requires that the unknown mechanism involve one or both major species: N2, O. Because of the rapidly decreasing volume mixing ratio (VMR) of CO2 with altitude, the exciting partner must be long lived and transfer energy efficiently. It is shown that thermal collisions with N2, mediated by a near-resonant rotation-to-vibration (RV) energy transfer process, while giving a reasonable rate coefficient kVR for de-excitation of the bending mode of CO2, lead to vibration-to-translation kVT rate coefficients in the terrestrial atmosphere that are 1–2 orders of magnitude larger than those observed in the laboratory. It is pointed out that the efficient near-resonant rotation-to-vibration (RV) energy transfer process has a chance of being the unknown mechanism if very high rotational levels of N2, produced by the reaction of N and NO and other collisional processes, have a super-thermal population and are long lived. Since atomic oxygen plays a critical role in the mechanisms discussed here, it suggested that its density be determined experimentally by ground- and space-based Raman lidars proposed earlier.
29
Avsarkisov, Victor, Erich Becker i Toralf Renkwitz. "Turbulent Parameters in the Middle Atmosphere: Theoretical Estimates Deduced from a Gravity Wave–Resolving General Circulation Model". Journal of the Atmospheric Sciences 79, nr 4 (kwiecień 2022): 933–52. http://dx.doi.org/10.1175/jas-d-21-0005.1.
Pełny tekst źródłaStreszczenie:
Abstract We present a scaling analysis for the stratified turbulent and small-scale turbulent regimes of atmospheric flow with emphasis on the mesosphere. We distinguish rotating-stratified macroturbulence turbulence (SMT), stratified turbulence (ST), and small-scale isotropic Kolmogorov turbulence (KT), and we specify the length and time scales and the characteristic velocities for these regimes. It is shown that the buoyancy scale (Lb) and the Ozmidov scale (Lo) are the main parameters that describe the transition from SMT to KT. We employ the buoyancy Reynolds number and horizontal Froude number to characterize ST and KT in the mesosphere. This theory is applied to simulation results from a high-resolution general circulation model with a Smagorinsky-type turbulent diffusion scheme for the subgrid-scale parameterization. The model allows us to derive the turbulent root-mean-square (rms) velocity in the KT regime. It is found that the turbulent RMS velocity has a single maximum in summer and a double maximum in winter months. The secondary maximum in the winter MLT we associate with a secondary gravity wave–breaking phenomenon. The turbulent rms velocity results from the model agree well with full correlation analyses based on MF-radar measurements. A new scaling for the mesoscale horizontal velocity based on the idea of direct energy cascade in mesoscales is proposed. The latter findings for mesoscale and small-scale characteristic velocities support the idea proposed in this research that mesoscale and small-scale dynamics in the mesosphere are governed by SMT, ST, and KT in the statistical average. Significance Statement Mesoscale dynamics in the middle atmosphere, which consists of atmospheric turbulence and gravity waves, remains a complex problem for atmospheric physics and climate studies. Due to its high nonlinearity, the mesoscale dynamics together with the small-scale turbulence is the primary source of uncertainties and biases in high-altitude general circulation models (GCM) in the middle atmosphere. We use the stratified turbulence theory and the gravity wave–resolving GCM to characterize different scaling regimes and to define various length, time, and velocity scales, that are relevant for the mesoscale and small-scale dynamical regimes. Our results highlight the importance of stratified turbulence in the mesosphere and lower-thermosphere region.
30
Waalewijn, R. A. "Problemen met de circulatie (C: Circulation)". Bijblijven 19, nr 7 (lipiec 2003): 287–95. http://dx.doi.org/10.1007/bf03059727.
Pełny tekst źródła
31
Chen, Dan, Cornelia Strube, Manfred Ern, Peter Preusse i Martin Riese. "Global analysis for periodic variations in gravity wave squared amplitudes and momentum fluxes in the middle atmosphere". Annales Geophysicae 37, nr 4 (2.07.2019): 487–506. http://dx.doi.org/10.5194/angeo-37-487-2019.
Pełny tekst źródłaStreszczenie:
Abstract. Atmospheric gravity waves (GWs) are an important coupling mechanism in the middle atmosphere. For instance, they provide a large part of the driving of long-period atmospheric oscillations such as the Quasi-Biennial Oscillation (QBO) and the semiannual oscillation (SAO) and are in turn modulated. They also induce the wind reversal in the mesosphere–lower thermosphere region (MLT) and the residual mean circulation at these altitudes. In this study, the variations in monthly zonal mean gravity wave square temperature amplitudes (GWSTAs) and, for the first time, absolute gravity wave momentum flux (GWMF) on different timescales such as the annual, semiannual, terannual and quasi-biennial variations are investigated by spectrally analyzing SABER observations from 2002 to 2015. Latitude–altitude cross sections of spectral amplitudes and phases of GWSTA and absolute GWMF in the stratosphere and mesosphere are presented and physically interpreted. It is shown that the time series of GWSTA and GWMF at a certain altitude and latitude results from the complex interplay of GW sources, propagation through and filtering in lower altitudes, oblique propagation superposing GWs from different source locations, and, finally, the modulation of the GW spectrum by the winds at a considered altitude and latitude. The strongest component is the annual variation, dominated in the summer hemisphere by subtropical convective sources and in the winter hemisphere by polar vortex dynamics. At heights of the wind reversal, a 180∘ phase shift also occurs, which is at different altitudes for GWSTA and GWMF. In the intermediate latitudes a semiannual variation (SAV) is found. Dedicated GW modeling is used to investigate the nature of this SAV, which is a different phenomenon from the tropical SAO also seen in the data. In the tropics a stratospheric and a mesospheric QBO are found, which are, as expected, in antiphase. Indication for a QBO influence is also found at higher latitudes. In previous studies a terannual variation (TAV) was identified. In the current study we explain its origin. In particular the observed patterns for the shorter periods, SAV and TAV, can only be explained by poleward propagation of GWs from the lower-stratosphere subtropics into the midlatitude and high-latitude mesosphere. In this way, critical wind filtering in the lowermost stratosphere is avoided and this oblique propagation is hence likely an important factor for MLT dynamics.
32
Manson, A. H., C. Meek, M. Hagan, J. Koshyk, S. Franke, D. Fritts, C. Hall i in. "Seasonal variations of the semi-diurnal and diurnal tides in the MLT: multi-year MF radar observations from 2–70° N, modelled tides (GSWM, CMAM)". Annales Geophysicae 20, nr 5 (31.05.2002): 661–77. http://dx.doi.org/10.5194/angeo-20-661-2002.
Pełny tekst źródłaStreszczenie:
Abstract. In an earlier paper (Manson et al., 1999a) tidal data (1990–1997) from six Medium Frequency Radars (MFR) were compared with the Global Scale Wave Model (GSWM, original 1995 version). The radars are located between the equator and high northern latitudes: Christmas Island (2° N), Hawaii (22° N), Urbana (40° N), London (43° N), Saskatoon (52° N) and Tromsø (70° N). Common harmonic analysis was applied, to ensure consistency of amplitudes and phases in the 75–95 km height range. For the diurnal tide, seasonal agreements between observations and model were excellent while for the semi-diurnal tide the seasonal transitions between clear solstitial states were less well captured by the model. Here the data set is increased by the addition of two locations in the Pacific-North American sector: Yamagawa 31° N, and Wakkanai 45° N. The GSWM model has undergone two additional developments (1998, 2000) to include an improved gravity wave (GW) stress parameterization, background winds from UARS systems and monthly tidal forcing for better characterization of seasonal change. The other model, the Canadian Middle Atmosphere Model (CMAM) which is a General Circulation Model, provides internally generated forcing (due to ozone and water vapour) for the tides. The two GSWM versions show distinct differences, with the 2000 version being either closer to, or further away from, the observations than the original 1995 version. CMAM provides results dependent upon the GW parameterization scheme inserted, but one of the schemes provides very useful tides, especially for the semi-diurnal component.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)
33
Tulegenov, Beket, Joachim Raeder, William D. Cramer, Banafsheh Ferdousi, Timothy J. Fuller-Rowell, Naomi Maruyama i Robert J. Strangeway. "Storm time polar cap expansion: interplanetary magnetic field clock angle dependence". Annales Geophysicae 41, nr 1 (16.01.2023): 39–54. http://dx.doi.org/10.5194/angeo-41-39-2023.
Pełny tekst źródłaStreszczenie:
Abstract. It is well known that the polar cap, delineated by the open–closed field line boundary (OCB), responds to changes in the interplanetary magnetic field (IMF). In general, the boundary moves equatorward when the IMF turns southward and contracts poleward when the IMF turns northward. However, observations of the OCB are spotty and limited in local time, making more detailed studies of its IMF dependence difficult. Here, we simulate five solar storm periods with the coupled model consisting of the Open Geospace General Circulation Model (OpenGGCM) coupled with the Coupled Thermosphere Ionosphere Model (CTIM) and the Rice Convection Model (RCM), i.e., the OpenGGCM-CTIM-RCM, to estimate the location and dynamics of the OCB. For these events, polar cap boundary location observations are also obtained from Defense Meteorological Satellite Program (DMSP) precipitation spectrograms and compared with the model output. There is a large scatter in the DMSP observations and in the model output. Although the model does not predict the OCB with high fidelity for every observation, it does reproduce the general trend as a function of IMF clock angle. On average, the model overestimates the latitude of the open–closed field line boundary by 1.61∘. Additional analysis of the simulated polar cap boundary dynamics across all local times shows that the MLT of the largest polar cap expansion closely correlates with the IMF clock angle, that the strongest correlation occurs when the IMF is southward, that during strong southward IMF the polar cap shifts sunward, and that the polar cap rapidly contracts at all local times when the IMF turns northward.
34
Saputra, Bobby Rifki, Asri Nugrahanti i Rizki Akbar. "ANALISIS METODE CASING WHILE DRILLING UNTUK SETTING CASING 16” PADA SUMUR C2". PETRO 7, nr 4 (20.04.2019): 159. http://dx.doi.org/10.25105/petro.v7i4.4284.
Pełny tekst źródłaStreszczenie:
<p><em>C2 well is an exploration well located in south sumatera area managed by PT. MEPI in</em><em> </em><em>planned CSS field will be drilled to a depth of 12.000 ftTVD vertically. Planning the use of casing while drilling is done by usin</em><em>g </em><em>16" protective casing</em><em> </em><em>on the trajectory 17-1/2" from a depth of 1.500 ft to 4.600 ft. The use of casing while drilling (CWD), is expected by using the casing as drillstring, then the clearance between the boreholes wall with the OD casing becomes small which will cause the event "Plastering Effect". This phenomenon is expected to isolate the wall of the drill hole which is easy to happen lost circulation. On vertical wells only need a casing method while drilling level-2 (non-retrievable) because at level-2 only casing with bits (drillshoe) only, where drillshoe will be left in the shoe casing. From the analysis results can be said on well C2 can be applied casing method while drilling because in terms of hydraulics drilling </em><em>which</em><em> the drill hole clearance with horsepower square inch method (HSI) and cutting lift based on cutting carrying index (CCI) is good, but </em><em>for</em><em> mechanics drilling needs to be considered torque, drag, and buckling loads. In terms of torque loads MLT Rings should be installed</em><em> </em><em>for 16” protective casing,</em><em> </em><em>from drag loads where the 2.000 HP rig can withstand maximum load of hookload, and 16" protective casing might not occur buckling as the maximum weight on bit (WOB) is still under critical buckling load.</em><em></em></p>
35
Hayden, K. L., D. M. L. Sills, J. R. Brook, S. M. Li, P. A. Makar, M. Z. Markovic, P. Liu i in. "Aircraft study of the impact of lake-breeze circulations on trace gases and particles during BAQS-Met 2007". Atmospheric Chemistry and Physics Discussions 11, nr 4 (13.04.2011): 11497–546. http://dx.doi.org/10.5194/acpd-11-11497-2011.
Pełny tekst źródłaStreszczenie:
Abstract. High time-resolved aircraft data, concurrent surface measurements and air quality model simulations were explored to diagnose the processes influencing aerosol chemistry under the influence of lake-breeze circulations in a polluted region of southwestern Ontario, Canada. The analysis was based upon horizontal aircraft transects at multiple altitudes across an entire lake-breeze circulation. Air mass boundaries due to lake-breeze fronts were identified in the aircraft meteorological and chemical data, which were consistent with the frontal locations determined from surface analyses. Observations and modelling support the interpretation of a lake-breeze circulation where pollutants were lofted at a lake-breeze front, transported in the synoptic flow, caught in a downdraft over the lake, and then confined by onshore flow. The detailed analysis led to the development of conceptual models that summarize the complex 3-D circulation patterns and their interaction with the synoptic flow. The identified air mass boundaries, the interpretation of the lake-breeze circulation, and best estimates for air parcel circulation times in the lake-breeze circulation (1.2 to 3.0 h) enabled formation rates of oxygenated organic aerosol (OOA/ΔCO) and SO42− to be determined. The formation rate for OOA, relative to excess CO, was found to be 2.5–6.2 μg m−3 ppmv−1 h−1 and the SO42− formation rate was 1.8–4.6% h−1. The formation rates are enhanced relative to regional background rates implying that lake-breeze circulations are an important dynamic in the formation of SO42− and secondary organic aerosol. The presence of cumulus clouds associated with the lake-breeze fronts suggests that these enhancements could be due to cloud processes. Additionally, the effective confinement of pollutants along the shoreline may have limited pollutant dilution leading to elevated oxidant concentrations.
36
Hayden, K. L., D. M. L. Sills, J. R. Brook, S. M. Li, P. A. Makar, M. Z. Markovic, P. Liu i in. "Aircraft study of the impact of lake-breeze circulations on trace gases and particles during BAQS-Met 2007". Atmospheric Chemistry and Physics 11, nr 19 (10.10.2011): 10173–92. http://dx.doi.org/10.5194/acp-11-10173-2011.
Pełny tekst źródłaStreszczenie:
Abstract. High time-resolved aircraft data, concurrent surface measurements and air quality model simulations were explored to diagnose the processes influencing aerosol chemistry under the influence of lake-breeze circulations in a polluted region of southwestern Ontario, Canada. The analysis was based upon horizontal aircraft transects conducted at multiple altitudes across an entire lake-breeze circulation. Air mass boundaries due to lake-breeze fronts were identified in the aircraft meteorological and chemical data, which were consistent with the frontal locations determined from surface analyses. Observations and modelling support the interpretation of a lake-breeze circulation where pollutants were lofted at a lake-breeze front, transported in the synoptic flow, caught in a downdraft over the lake, and then confined by onshore flow. The detailed analysis led to the development of conceptual models that summarize the complex 3-D circulation patterns and their interaction with the synoptic flow. The identified air mass boundaries, the interpretation of the lake-breeze circulation, and the air parcel circulation time in the lake-breeze circulation (3.0 to 5.0 h) enabled formation rates of organic aerosol (OA/ΔCO) and SO42− to be determined. The formation rate for OA (relative to excess CO in ppmv) was found to be 11.6–19.4 μg m−3 ppmv−1 h−1 and the SO42− formation rate was 5.0–8.8% h−1. The formation rates are enhanced relative to regional background rates implying that lake-breeze circulations are an important dynamic in the formation of SO42− and secondary organic aerosol. The presence of cumulus clouds associated with the lake-breeze fronts suggests that these enhancements could be due to cloud processes. Additionally, the effective confinement of pollutants along the shoreline may have limited pollutant dilution leading to elevated oxidant concentrations.
37
Song, Botao, Yufeng Luo, Senlin Rao, Fayun Zhang i Yun Hu. "Analysis of the Effect of a Vertical Magnetic Field on Melt Convection and Oxygen Transport During Directional Solidification of Multi-Crystalline Silicon by Numerical Simulation". Crystals 10, nr 1 (23.12.2019): 8. http://dx.doi.org/10.3390/cryst10010008.
Pełny tekst źródłaStreszczenie:
Melt convection during the directional solidification process of multi-crystalline silicon plays a critical role in the transport of impurities. The utilization of a static magnetic field is an effective way to control the melt convection pattern. Studying the effect of the Lorentz force induced by the vertical magnetic field (VMF) on the melt convection of silicon in detail is beneficial to optimize the magnetic field parameters in the production process. Based on the numerical simulation method of multi-physics coupling, this paper explores the effects of different VMF intensities on the convection of silicon melt and the transport of oxygen in the melt during the directional solidification of polycrystalline silicon. The results show that in the first 125 minutes of the crystallization stage, the melt convection velocity is affected significantly by the magnetic field intensities. When different convection circulations are present in the silicon melt, the upper circulation easily transports oxygen to the furnace atmosphere, and the subjacent circulation easily lead to the retention and accumulation of oxygen. Enhancing the VMF intensity to a certain extent can reduce the size of the oxygen retention region in the silicon melt, and the time of the first disappearance of the subjacent circulation near the sidewall of the crucible is shortened. Then the average oxygen concentration in the silicon melt can be reduced. However, a larger vertical magnetic field intensity can result in greater average oxygen concentration in the oxygen retention region.
38
Somberg, John C. "Hypoxia and the Circulation". American Journal of Therapeutics 16, nr 3 (maj 2009): 280. http://dx.doi.org/10.1097/mjt.0b013e3181728550.
Pełny tekst źródła
39
Farrell, Martin V., i Nancy Ma. "Coupling of Buoyant Convections in Boron Oxide and a Molten Semiconductor in a Vertical Magnetic Field". Journal of Heat Transfer 124, nr 4 (16.07.2002): 643–49. http://dx.doi.org/10.1115/1.1473141.
Pełny tekst źródłaStreszczenie:
This paper treats the buoyant convection in a layer of boron oxide, called a liquid encapsulant, which lies above a layer of a molten compound semiconductor (melt) between cold and hot vertical walls in a rectangular container with a steady vertical magnetic field B. The magnetic field provides an electromagnetic (EM) damping of the molten semiconductor which is an excellent electrical conductor but has no direct effect on the motion of the liquid encapsulant. The temperature gradient drives counter clockwise circulations in both the melt and encapsulant. These circulations alone would lead to positive and negative values of the horizontal velocity in the encapsulant and melt, respectively, near the interface. The competition between the two buoyant convections determines the direction of the horizontal velocity of the interface. For B=5 T, there is significant EM damping of the melt motion and the encapsulant drives a positive interfacial velocity and a small clockwise circulation in the melt. For a much weaker field B=0.1 T, the maximum velocity in the melt is hundreds of times larger than that of the encapsulant, thus causing nearly all the encapsulant to circulate in the clockwise direction.
40
Webber, Benjamin G. M., Karen J. Heywood, David P. Stevens i Karen M. Assmann. "The Impact of Overturning and Horizontal Circulation in Pine Island Trough on Ice Shelf Melt in the Eastern Amundsen Sea". Journal of Physical Oceanography 49, nr 1 (styczeń 2019): 63–83. http://dx.doi.org/10.1175/jpo-d-17-0213.1.
Pełny tekst źródłaStreszczenie:
AbstractThe ice shelves around the Amundsen Sea are rapidly melting as a result of the circulation of relatively warm ocean water into their cavities. However, little is known about the processes that determine the variability of this circulation. Here we use an ocean circulation model to diagnose the relative importance of horizontal and vertical (overturning) circulation within Pine Island Trough, leading to Pine Island and Thwaites ice shelves. We show that melt rates and southward Circumpolar Deep Water (CDW) transports covary over large parts of the continental shelf at interannual to decadal time scales. The dominant external forcing mechanism for this variability is Ekman pumping and suction on the continental shelf and at the shelf break, in agreement with previous studies. At the continental shelf break, the southward transport of CDW and heat is predominantly barotropic. Farther south within Pine Island Trough, northward and southward barotropic heat transports largely cancel, and the majority of the net southward temperature transport is facilitated by baroclinic and overturning circulations. The overturning circulation is related to water mass transformation and buoyancy gain on the shelf that is primarily facilitated by freshwater input from basal melting.
41
Le Bras, Isabela, Fiamma Straneo, Morven Muilwijk, Lars H. Smedsrud, Feili Li, M. Susan Lozier i N. Penny Holliday. "How Much Arctic Fresh Water Participates in the Subpolar Overturning Circulation?" Journal of Physical Oceanography 51, nr 3 (marzec 2021): 955–73. http://dx.doi.org/10.1175/jpo-d-20-0240.1.
Pełny tekst źródłaStreszczenie:
AbstractFresh Arctic waters flowing into the Atlantic are thought to have two primary fates. They may be mixed into the deep ocean as part of the overturning circulation, or flow alongside regions of deep water formation without impacting overturning. Climate models suggest that as increasing amounts of freshwater enter the Atlantic, the overturning circulation will be disrupted, yet we lack an understanding of how much freshwater is mixed into the overturning circulation’s deep limb in the present day. To constrain these freshwater pathways, we build steady-state volume, salt, and heat budgets east of Greenland that are initialized with observations and closed using inverse methods. Freshwater sources are split into oceanic Polar Waters from the Arctic and surface freshwater fluxes, which include net precipitation, runoff, and ice melt, to examine how they imprint the circulation differently. We find that 65 mSv (1 Sv ≡ 106 m3 s−1) of the total 110 mSv of surface freshwater fluxes that enter our domain participate in the overturning circulation, as do 0.6 Sv of the total 1.2 Sv of Polar Waters that flow through Fram Strait. Based on these results, we hypothesize that the overturning circulation is more sensitive to future changes in Arctic freshwater outflow and precipitation, while Greenland runoff and iceberg melt are more likely to stay along the coast of Greenland.
42
Hoechter, Dominik J., Yu-Ming Shen, Tobias Kammerer, Sabina Günther, Thomas Weig, René Schramm, Christian Hagl i in. "Extracorporeal Circulation During Lung Transplantation Procedures". ASAIO Journal 63, nr 5 (2017): 551–61. http://dx.doi.org/10.1097/mat.0000000000000549.
Pełny tekst źródła
43
SAHA, KSHUDIRAM, i SURANJANA SAHA. "On the monsoons of South America Part 1 : Climatological structure and circulation". MAUSAM 55, nr 1 (19.01.2022): 41–72. http://dx.doi.org/10.54302/mausam.v55i1.1124.
Pełny tekst źródłaStreszczenie:
Earth-atmosphere radiation budget analyses as well as conventional meteorological analyses are used to establish a case for a well-developed monsoon circulation over South America operating between a heat source over the continent and a heat sink over the surrounding oceans during the southern summer. Evidence is produced to show that the criterion of seasonal reversal is met not only by the wind field but also by the fields of several other variables, such as temperature, isobaric height, specific humidity and rainfall. Computed meridional-vertical circulations for different seasons appear to suggest that the onset and withdrawal of monsoon over the continent are related to the movement of Hadley and Monsoon circulation cells following the seasonal movement of the heat source. A revised definition of the monsoon is proposed in accordance with the findings of the study.
44
Giridharan, Guruprasad A., Mickey Ising, Michael A. Sobieski, Steven C. Koenig, Jun Chen, Steven Frankel i Mark D. Rodefeld. "Cavopulmonary Assist for the Failing Fontan Circulation". ASAIO Journal 60, nr 6 (2014): 707–15. http://dx.doi.org/10.1097/mat.0000000000000135.
Pełny tekst źródła
45
Camboni, Daniele, Sebastian Schmidt, Alois Philipp, Leopold Rupprecht, Assad Haneya, Thomas Puehler, Matthias Arlt, Michael Hilker i Christof Schmid. "Microbubble Activity in Miniaturized and in Conventional Extracorporeal Circulation". ASAIO Journal 55, nr 1 (styczeń 2009): 58–62. http://dx.doi.org/10.1097/mat.0b013e31818f3e8c.
Pełny tekst źródła
46
Sole, A. J., A. J. Payne, P. W. Nienow, P. Christoffersen, F. R. Cottier i M. E. Inall. "Increased glacier runoff enhances the penetration of warm Atlantic water into a large Greenland fjord". Cryosphere Discussions 6, nr 6 (27.11.2012): 4861–96. http://dx.doi.org/10.5194/tcd-6-4861-2012.
Pełny tekst źródłaStreszczenie:
Abstract. The retreat and acceleration of Greenland's marine-terminating outlet glaciers have been linked to ocean warming. However the mechanisms which control the transmission of this warming along fjords towards the glaciers remain poorly understood. The aim of this paper is to elucidate observed changes in water properties in Kangerdlugssuaq Fjord (KF), East Greenland using the Bergen Ocean Model (BOM). Model outputs are compared with observed potential temperature, salinity and velocity data to determine the principal controls on heat transport within KF and to estimate resulting submarine ice front melt rates of Kangerdlugssuaq Glacier (KG). The BOM includes wind, tidal and glacier runoff forcing and is able to replicate observed temperature and salinity profiles. Model results describe a robust four-layer estuarine flow, consisting of two distinct circulations. The shallow circulation (0–~ 60 m) is forced by surface wind stress and to a lesser extent supraglacial runoff, while the intermediate circulation (~ 60–500 m) is driven by runoff discharged into the fjord subglacially. Atlantic Water (AW) and warm Polar Surface Water (PSWw) are drawn into the fjord by the intermediate and shallow circulation cells respectively, in a pattern consistent with observations, and AW reaches KG over a single summer. Along-fjord heat transport towards KG increases significantly with both glacier runoff and coastal water temperature. A doubling of glacier runoff produces a 29% (48%) amplification of mean annual (summer) heat transport towards the KG terminus, increasing estimated mean annual (summer) submarine melt rates from 211 to 273 (842 to 1244) m yr–1. In contrast, heat transport towards KG in the surface ~ 60 m of the fjord decreases with rising glacier runoff because the enhanced down-fjord component of the intermediate circulation interferes with the up-fjord part of the shallow circulation. Thus, as ice sheet runoff increases, KG's dynamic response to oceanic forcing will likely be driven primarily by enhanced submarine ice front melting and consequent undercutting rather than through diminished buttressing from seasonal sea ice and ice mélange. Our model shows, in agreement with observations, that maximum submarine melt rates occur when AW and PSWw are present at the fjord mouth and, crucially, glacier runoff is also high. Rising ice sheet runoff therefore increases the sensitivity of KG (and other Greenland marine-terminating glaciers) to ocean warming.
47
Mayne, N. J., I. Baraffe, D. M. Acreman, C. Smith, N. Wood, D. Skålid Amundsen, J. Thuburn i D. R. Jackson. "Using the UM dynamical cores to reproduce idealised 3-D flows". Geoscientific Model Development Discussions 6, nr 3 (12.07.2013): 3681–741. http://dx.doi.org/10.5194/gmdd-6-3681-2013.
Pełny tekst źródłaStreszczenie:
Abstract. We demonstrate that both the current (New Dynamics), and next generation (ENDGame) dynamical cores of the UK Met Office global circulation model, the UM, reproduce consistently, the long-term, large-scale flows found in several published idealised tests. The cases presented are the Held–Suarez test, a simplified model of Earth (including a stratosphere), and a model of a hypothetical Tidally Locked Earth (TLE). Furthermore, we show that using simplifications to the dynamical equations, which are expected to be justified for the physical domains and flow regimes we have studied, and which are supported by the ENDGame dynamical core, also produces matching long-term, large-scale flows. Finally, we present evidence for differences in the detail of the planetary (meridional) flows and circulations resulting from improvements in the ENDGame formulation over New Dynamics. Specifically, we find greater symmetry in the meridional circulations of the Tidally Locked Earth test case using the ENDGame formulation, which is a better match to our physical expectations of the flow for such a slowly rotating Earth-like system.
48
Scheving, Lawrence A., Xiuqi Zhang, Mary C. Stevenson, David W. Threadgill i William E. Russell. "Loss of hepatocyte EGFR has no effect alone but exacerbates carbon tetrachloride-induced liver injury and impairs regeneration in hepatocyte Met-deficient mice". American Journal of Physiology-Gastrointestinal and Liver Physiology 308, nr 5 (1.03.2015): G364—G377. http://dx.doi.org/10.1152/ajpgi.00364.2014.
Pełny tekst źródłaStreszczenie:
The role(s) of the epidermal growth factor receptor (EGFR) in hepatocytes is unknown. We generated a murine hepatocyte specific-EGFR knockout (KO) model to evaluate how loss of hepatocellular EGFR expression affects processes such as EGF clearance, circulating EGF concentrations, and liver regeneration following 70% resection or CCl4-induced centrilobular injury. We were able to disrupt EGFR expression effectively in hepatocytes and showed that the ability of EGF and heregulin (HRG) to phosphorylate EGFR and ERBB3, respectively, required EGFR. Loss of hepatocellular EGFR impaired clearance of exogenous EGF from the portal circulation but paradoxically resulted in reduced circulating levels of endogenous EGF. This was associated with decreased submandibular salivary gland production of EGF. EGFR disruption did not result in increased expression of other ERBB proteins or Met, except in neonatal mice. Liver regeneration following 70% hepatectomy revealed a mild phenotype, with no change in cyclin D1 expression and slight differences in cyclin A expression compared with controls. Peak 5-bromo-2′-deoxyuridine labeling was shifted from 36 to 48 h. Centrilobular damage and regenerative response induced by carbon tetrachloride (CCl4) were identical in the KO and wild-type mice. In contrast, loss of Met increased CCl4-induced necrosis and delayed regeneration. Although loss of hepatocellular EGFR alone did not have an effect in this model, EGFR-Met double KOs displayed enhanced necrosis and delayed liver regeneration compared with Met KOs alone. This suggests that EGFR and Met may partially compensate for the loss of the other, although other compensatory mechanisms can be envisioned.
49
Birch, Cathryn E., Malcolm J. Roberts, Luis Garcia-Carreras, Duncan Ackerley, Michael J. Reeder, Adrian P. Lock i Reinhard Schiemann. "Sea-Breeze Dynamics and Convection Initiation: The Influence of Convective Parameterization in Weather and Climate Model Biases". Journal of Climate 28, nr 20 (13.10.2015): 8093–108. http://dx.doi.org/10.1175/jcli-d-14-00850.1.
Pełny tekst źródłaStreszczenie:
Abstract There are some long-established biases in atmospheric models that originate from the representation of tropical convection. Previously, it has been difficult to separate cause and effect because errors are often the result of a number of interacting biases. Recently, researchers have gained the ability to run multiyear global climate model simulations with grid spacings small enough to switch the convective parameterization off, which permits the convection to develop explicitly. There are clear improvements to the initiation of convective storms and the diurnal cycle of rainfall in the convection-permitting simulations, which enables a new process-study approach to model bias identification. In this study, multiyear global atmosphere-only climate simulations with and without convective parameterization are undertaken with the Met Office Unified Model and are analyzed over the Maritime Continent region, where convergence from sea-breeze circulations is key for convection initiation. The analysis shows that, although the simulation with parameterized convection is able to reproduce the key rain-forming sea-breeze circulation, the parameterization is not able to respond realistically to the circulation. A feedback of errors also occurs: the convective parameterization causes rain to fall in the early morning, which cools and wets the boundary layer, reducing the land–sea temperature contrast and weakening the sea breeze. This is, however, an effect of the convective bias, rather than a cause of it. Improvements to how and when convection schemes trigger convection will improve both the timing and location of tropical rainfall and representation of sea-breeze circulations.
50
Richenbacher, Wayne E. "Latest Developments in the Field of Assisted Circulation". ASAIO Journal 51, nr 6 (listopad 2005): xv—xx. http://dx.doi.org/10.1097/01.mat.0000186661.32538.22.
Pełny tekst źródła