Academic literature on the topic 'Atmospheric circulation Northern Territory Darwin'

Abstract Two field campaigns, the African Monsoon Multidisciplinary Analysis (AMMA) and the Tropical Warm Pool–International Cloud Experiment (TWP-ICE), took place in 2006 near Niamey, Niger, and Darwin, Northern Territory, Australia, providing extensive observations of mesoscale convective systems (MCSs) near a desert and a tropical coast, respectively. Under the constraint of their observations, three-dimensional cloud-resolving model simulations are carried out and presented in this paper to replicate the basic characteristics of the observed MCSs. All of the modeled MCSs exhibit a distinct structure having deep convective clouds accompanied by stratiform and anvil clouds. In contrast to the approximately 100-km-scale MCSs observed in TWP-ICE, the MCSs in AMMA have been successfully simulated with a scale of about 400 km. These modeled AMMA and TWP-ICE MCSs offer an opportunity to understand the structure and mechanism of MCSs. Comparing the water budgets between AMMA and TWP-ICE MCSs suggests that TWP-ICE convective clouds have stronger ascent while the mesoscale ascent outside convective clouds in AMMA is stronger. A case comparison, with the aid of sensitivity experiments, also suggests that vertical wind shear and ice crystal (or dust aerosol) concentration can significantly impact stratiform and anvil clouds (e.g., their areas) in MCSs. In addition, the obtained water budgets quantitatively describe the transport of water between convective, stratiform, and anvil regions as well as water sources/sinks from microphysical processes, providing information that can be used to help determine parameters in the convective and cloud parameterizations in general circulation models (GCMs).

Abstract The passage of three Australian Category 5 cyclones within 350 km of Darwin (Northern Territory), Australia, during the last decade indicates that that city should have a high wind hazard. In this paper, the wind hazard for Darwin was compared with that for Port Hedland (Western Australia) and Townsville (Queensland) using data from a coupled ocean–atmosphere simulation model and from historical and satellite-era records of tropical cyclones. According to the authoritative statement on wind hazard in Australia, Darwin’s wind hazard is the same as Townsville’s but both locations’ hazards are much less than that of Port Hedland. However, three different estimates in this study indicate that Darwin’s wind hazard at the long return periods relevant to engineering requirements is higher than for both Port Hedland and Townsville. The discrepancy with previous studies may result from the inadequate cyclone records in the low-latitude north of Australia, from accumulated errors from estimates of wind speeds from wind fields and wind–pressure relationships, and from inappropriate extrapolations of short-period records based on assumed probability distributions. It is concluded that the current wind-hazard zoning of northern Australia seriously underestimates the hazard near Darwin and that coupled ocean–atmosphere simulation models could contribute to its revision.

The paper presents the results of research conducted on large-scale and zonal atmospheric factors of climate variability over the territory of the Baikal region, which, according to Russian Federal Service for Hydrometeorology and Environmental Monitoring (Roshydromet) is considered to be one of the regions characterized by highest rates of climate change. On the basis of trend, correlation, and spectrum analyses, investigation was made of high- and low-frequency components in multidecadal timescales of climatic indices dynamics, which determine and distinguish variability in pressure fields and geopotential at high latitudes in the Northern hemisphere, in the northern parts of the Atlantic and Pacific oceans throughout the time period of 1950–2017. In the dynamics of climate indices, cyclicity is manifested. It reflects the contribution of short-term and long-term variations, which are close in duration to the variability of continental and oceanic centers of atmospheric action in the Northern Hemisphere. Among climatic indices, the highest levels of correlation with changes in average monthly temperatures in the city of Irkutsk can be traced for the Scandinavian index. With an increase in surface pressure in the territory of Scandinavia, the contribution of advective heat and moisture fluxes from the Atlantic is weakened. The latter have a warming effect in the winter months on the territory of the Irkutsk region. Particular emphasis was put on searching for causes of increasingly arid climate in the Baikal region in summer months of 2000–2017, when the number of forest fires in the region rose dramatically.

AbstractCook and Nicholls recently argued in this journal that the city of Darwin (Northern Territory), Australia, should be located in wind region D rather than in the current region C in the Australian/New Zealand Standard AS/NZS 1170.2 wind actions standard, in which region D has significantly higher risk. These comments critically examine the methods used by Cook and Nicholls and find serious flaws in them, sufficient to invalidate their conclusions. Specific flaws include 1) invalid assumptions in their analysis method, including that cyclones are assumed to be at the maximum intensity along their entire path across the sampling circle even after they have crossed extensive land areas; 2) a lack of verification that the simulated cyclone tracks are consistent with the known climatological data and in particular that the annual rate of simulated cyclones at each station greatly exceeds the numbers recorded for the entire Australian region; and 3) the apparent omission of key cyclones when comparing the risk at Darwin with two other locations. It is shown here that the number of cyclones that have affected Port Hedland (Western Australia), a site in Australia’s region D, greatly exceeds the number that have influenced Darwin over the same period for any chosen threshold of intensity. Analysis of the recorded gusts from anemometers at Port Hedland and Darwin that is presented here further supports this result. On the basis of this evidence, the authors conclude that Darwin’s tropical cyclone wind risk is adequately described by its current location in region C.

AbstractA reexamination of the wind hazard from tropical cyclones for the city of Darwin (Northern Territory), Australia, by Cook and Nicholls concluded that its wind hazard is substantially underestimated by its allocation to region C in the Australian wind code. This conclusion was dismissed by Harper et al. on the basis of interpretation of anemometer records and Dvorak central pressure estimates as well as criticism of the simple technique and data used to interpret historic records. Of the 44 years of historical anemometer records presented by Harper et al. for Darwin, however, only one record was for a direct hit by an intense tropical cyclone. The other records derive from distant and/or weak tropical cyclones, which are not applicable to understanding the wind hazard at long return periods. The Dvorak central pressure estimates from which Harper et al. conclude that Port Hedland (Western Australia), Australia, has a greater wind hazard than Darwin does, when back transformed to Dvorak current-intensity values and gust speeds, indicate the converse. The simple technique used to derive wind hazard from historical cyclone occurrence is defended in detail and shown to produce estimates of wind hazard that are close to those accepted for five locations on the hurricane-affected coastline of the U.S. mainland. Thus the criticisms by Harper et al. of Cook and Nicholl’s work are shown to be invalid and the original conclusion that Darwin’s wind hazard is substantially underestimated in the current Australian wind code is supported.

Based on assessments of the meteorological services of the CIS countries, the skill scores of the consensus forecast for the territory of Northern Eurasia for the summer of 2021 are presented. The results of monitoring circulation patterns in the stratosphere and troposphere over the past summer season are discussed. Climate monitoring and seasonal forecasting results for the current situation are presented. A probabilistic consensus forecast for air temperature and precipitation is presented for the upcoming winter season 2021/2022 in Northern Eurasia. Possible consequences of the impact of the expected anomalies of meteorological parameters on the economy sectors and social life are discussed. Keywords: North Eurasian Climate Forum, North Eurasian Climate Center, consensus forecast, air temperature, precipitation, large-scale atmospheric circulation, hydrodynamic models, sea surface temperature, impacts

The paper considers the modern problems in prediction of hazardous geological processes in the XXI century. It is noted that the peculiarities of the prediction of the most hazardous geological processes (landslides, mudflows, etc.) are connected with global climatic changes and a technogenic factor. The assessment of climatic changes and the most largest catastrophic disasters was carried out with use of the typification of atmospheric circulation in the Northern hemisphere, developed by B. L. Dzerdzeevskii. The data of the typification for the period from 1899 to 2017 can be found on the Internet website www. atmospheric-circulation.ru in open access. The major disasters are considered that caused an activation of landslides and mudflows. The interaction of natural and technogenic factors is described during these disasters. The prediction took into consideration the changes in solar activity and features of space weather.

The Walker circulation is linked to extratropical waves that are deflected from the Northern Hemisphere polar regions and travel southeastward over central Asia toward the western Pacific warm pool during northern winter. The wave pattern resembles the east Atlantic–west Russia pattern and influences the El Niño–Southern Oscillation (ENSO) region. A tripole pattern between the West Siberian Plain and the two centers of action of ENSO indicates that the background state of ENSO with respect to global sea level pressure (SLP) has a significant negative correlation to the West Siberian Plain. The correlation with the background state, which is defined by the sum of the two centers of action of ENSO, is higher than each of the pairwise correlations with either of the ENSO centers alone. The centers are defined with a clustering algorithm that detects regions with similar characteristics. The normalized monthly SLP time series for the two centers of ENSO (around Darwin, Australia, and Tahiti) are area averaged, and the sum of both regions is considered as the background state of ENSO. This wave train can be detected throughout the troposphere and the lower stratosphere. Its origins can be traced back to Rossby wave activity triggered by convection over the subtropical North Atlantic that emanates wave activity toward the West Siberian Plain. The same wave train also propagates to the central Pacific Ocean around Tahiti and can be used to predict the background state over the ENSO region. This background state also modifies the subtropical bridge between tropical eastern Pacific and subtropical North Atlantic leading to a circumglobal wave train.

According to the circulation seasons [Dzerdzeevsky et al., 1946], according to the website Weather News, extreme events in the Asian territory of Russia for first half of 2019 were considered: daily maximums and minimums of air temperature; maximum daily amplitudes of air temperature, daily maximums and monthly lows of atmospheric precipitation; daily maximums wind speeds, maximum and minimum of snow depths and dangerous natural processes. Their connection with the atmospheric circulation of the Northern Hemisphere has been shown [Atmospheric Circulation fluctuations site 18992018]. In recent years, extreme situations are increasingly becoming apparent in the Asian part of Russia. This attracts the close attention of researchers [Latysheva et al., 2010; Zolina, Bulygina, 2016]. They try to identify the causes of what is happening [Vasilyev et al., 2018; Kononova, 2018; Kochugova, 2018; Tarabukina et al., 2018] and predict the future nature of extrema [Shkolnik et al., 2012]. It seemed interesting to analyze the extremes of the current year (more precisely, the first half of it), to show the real situation today. The majority of extremes, surpassed in the first half of 2019, refers to the 21st century. This means that extremity has been growing rapidly in recent years. The consequence of this is an increase in the frequency of occurrence of dangerous natural processes. The main source of information on daily meteorological extremes was Weather News [Meteonovosti.ru]. It briefly informed about fires and floods. More detailed information was taken from local sites [Amur.Info, Taiga.Info, Ulpress.ru, Social media news]. The character of atmospheric circulation was analyzed by classification [Dzerdzeevsky et al., 1946] using data from the site of the Atmospheric Circulation fluctuations.. for 1899 2018 The most disastrous flood was June 24 - 29 in the Irkutsk region. It destroyed more than 10,000 residential homes in 98 settlements, 43 schools, kindergartens and hospitals. According to information on July 11, 25 people died. The strongest were fires in the Krasnoyarsk Territory and the Irkutsk Region in the third decade of July. Smoke from them reached the Ulyanovsk region. The conducted research allows to draw the following conclusions. The number of extremes of both air temperature and precipitation in the XXI century continues to grow. Negative extremes of precipitation in combination with positive extremes of air temperature lead to natural fires, positive extremes of precipitation - to catastrophic floods. The increasing frequency of atmospheric circulation contributes to an increase in the frequency of occurrence of those and others: an increase in the frequency of occurrence of blocking processes (arctic invasions resulting in the formation of a vast stationary anticyclone) and exits of southern cyclones.

AbstractComparisons between direct measurements and modeled values of vertical air motions in precipitating systems are complicated by differences in temporal and spatial scales. On one hand, vertically profiling radars more directly measure the vertical air motion but do not adequately capture full storm dynamics. On the other hand, vertical air motions retrieved from two or more scanning Doppler radars capture the full storm dynamics but require model constraints that may not capture all updraft features because of inadequate sampling, resolution, numerical constraints, and the fact that the storm is evolving as it is scanned by the radars. To investigate the veracity of radar-based retrievals, which can be used to verify numerically modeled vertical air motions, this article presents several case studies from storm events around Darwin, Northern Territory, Australia, in which measurements from a dual-frequency radar profiler system and volumetric radar-based wind retrievals are compared. While a direct comparison was not possible because of instrumentation location, an indirect comparison shows promising results, with volume retrievals comparing well to those obtained from the profiling system. This prompted a statistical analysis of an extended period of an active monsoon period during the Tropical Warm Pool International Cloud Experiment (TWP-ICE). Results show less vigorous deep convective cores with maximum updraft velocities occurring at lower heights than some cloud-resolving modeling studies suggest.