Atmospheric Centers Of Action Research Articles

Статистические оценки параметров центров действия атмосферы в зимнем и летнем сезонах по данным реанализа за период 1992–2021 годов

The subject of the present study is climatological atmospheric centers of action (permanent and seasonal) of the Northern and Southern hemispheres for the central months of the winter and summer seasons. Data on 1000 hPa geopotential height from the NCEP/DOE AMIP-II reanalysis of atmospheric parameters for 1992-2021 are used as initial information. Software-implemented processing of long-term reanalysis data files made it possible to map of the distribution of synoptic centers of action at regular grid points (with a step of 2.5 in latitude and longitude). Statistical estimates of the parameters of atmospheric centers of action (location and intensity), including concentration ellipse characteristics, are presented. An analysis of the change in the characteristics as compared to the base climate period of 1961–1990 (according to the NCEP/NCAR reanalysis data) is given. The dynamics of the characteristics of the centers of action in the form of moving 10-year averages for 2000–2021 is demonstrated. Keywords: atmospheric center of action, reanalysis, geopotential height, concentration ellipse, moving average, trend

Atmospheric Centers of Action in the Northern Hemisphere: Current Features and Expected Changes in the 21st Century Based on Simulations with the CMIP5 and CMIP6 Ensembles of Climate Models

Atmospheric Centers of Action in the Northern Hemisphere: Current Features and Expected Changes in the 21st Century Based on Simulations with the CMIP5 and CMIP6 Ensembles of Climate Models

“Beyond Weather Regimes”: Descriptors Monitoring Atmospheric Centers of Action. A case study for Aotearoa New Zealand

AbstractThis paper introduces a set of descriptors applied to weather regimes, that allow for a detailed monitoring of the location and intensity of their atmospheric centers of action (e.g. troughs and ridges) and the gradients between them, when applicable. Descriptors are designed to document the effect of climate variability and change in modulating the character of daily weather regimes, rather than merely their occurrence statistics.As a case study, the methodology is applied to Aotearoa New Zealand (ANZ), using ERA5 ensemble reanalysis data for the period 1979-2019. Here, we analyze teleconnections between the regimes and their descriptors, and large-scale climate variability. Results show a significant modulation of centers of action by the phase of the Southern Annular Mode, with a strong relationship identified with the latitude of atmospheric ridges. Significant associations with El Niño Southern Oscillation are also identified. Modes of large-scale variability have a stronger influence on the regimes’ intrinsic features than their occurrence. This demonstrates the usefulness of such descriptors, which help understand the relationship between mid-latitude transient perturbations and large-scale modes of climate variability.In future research, this methodological framework will be applied to analyze (i) low-frequency changes in weather regimes under climate change, in line with the southward shift of storm tracks, and (ii) regional-scale effects on the climate of ANZ, resulting from interaction with its topography.

Climatic Changes of Thermal Conditions in the Pacific Subarctic at the Modern Stage of Global Warming

Purpose. The study is aimed at identifying the regional features of the surface air temperature in the coastal zone and over the Pacific Ocean (to the north of 40° N) manifested as a result of global climate changes at the turn of the XX–XXI centuries, and at assessing their trends and possible causal relationships with the processes in the atmosphere and on the ocean surface. Methods and Results. Based on the Global Meteorological Network and NOAA reanalysis data, the regional features of interannual oscillations of the surface air temperature and their relationship with variations in the fields of pressure, wind and water temperature on the ocean surface, and with climate indices over the past 4 decades were identified. In order to determine the temperature field spatial-temporal structure and to zone the water area according to the features of climate changes, the methods of cluster, correlation analysis and the apparatus of empirical orthogonal functions were used. The results obtained made it possible to characterize the degree of heterogeneity of the studied area response to the ongoing global changes, to identify different domains and to assess quantitatively the warming rate in these water areas. Conclusions. The tendencies of modern warming are manifested in the trends of interannual air temperature variability, on the average, by ~0.20°C/10 years in the subarctic, and indicate significant regional differences (1.5–2 times) in the ongoing changes. In the west of the region, the warming rate is higher than in the east, where the temperature trends are minimal or statistically insignificant. In the warm period of a year, their values are higher than those in the cold period. The alternation phases of the warm and cold periods are consistent with the variation tendencies in the characteristics both of the atmospheric action centers and various climatic parameters. The corresponding correlations are most widely manifested in variations in the empirical orthogonal functions modes of the H500 geopotential field, and the PDO, NP, SOI, PTW, AD and EP/NP indices. Stable anomalies and trends of the ocean surface temperature in the North Atlantic also play an important role in formation of the Та anomalies in the western subarctic.

Klimaticheskiye izmeneniya termicheskikh usloviy v tikhookeanskoy subarktike v usloviyakh sovremennogo global'nogo potepleniya

Purpose. The study is aimed at identifying the regional features of the surface air temperature in the coastal zone and over the Pacific Ocean (to the north of 40° N) manifested as a result of global climate changes at the turn of the XX–XXI centuries, and at assessing their trends and possible causal relationships with the processes in the atmosphere and on the ocean surface. Methods and Results. Based on the Global Meteorological Network and NOAA reanalysis data, the regional features of interannual fluctuations of the surface air temperature and their relationship with variations in the fields of pressure, wind and water temperature on the ocean surface, and with climate indices over the past 4 decades were identified. In order to determine the temperature field spatialtemporal structure and to zone the water area according to the features of climate changes, the methods of cluster, correlation analysis and the apparatus of empirical orthogonal functions were used. The results obtained made it possible to characterize the degree of heterogeneity of the studied area response to the ongoing global changes, to identify different domains and to assess quantitatively the warming rate in these water areas. Conclusions. The tendencies of modern warming are manifested in the trends of interannual air temperature variability, on the average, by ~0.20°C/10 years in the subarctic, and indicate significant regional differences (1.5–2 times) in the ongoing changes. In the west of the region, the warming rate is higher than in the east, where the temperature trends are minimal or statistically insignificant. In the warm period of a year, their values are higher than those in the cold period. The alternation phases of the warm and cold periods are consistent with the variation tendencies in the characteristics both of the atmospheric action centers and various climatic parameters. The corresponding correlations are most widely manifested in variations in the empirical orthogonal functions modes of the H500 geopotential field, and the PDO, NP, SOI, PTW, AD and EP/NP indices. Stable anomalies and trends of the ocean surface temperature in the North Atlantic also play an important role in formation of the Та anomalies in the western subarctic.

РЕГИОНАЛЬНЫЕ ОСОБЕННОСТИ МЕЖГОДОВЫХ ИЗМЕНЕНИЙ ТЕМПЕРАТУРЫ ВОДЫ В СУБАРКТИЧЕСКОЙ ЗОНЕ ТИХОГО ОКЕАНА

Based on the NOAA climate datasets, trends, regional features, and possible causal relationships of interannual variations in water temperature on the surface (SST) and in the upper 750-meter layer of the subarctic Pacific with variations in the fields of air temperature, air pressure, wind, and climate indices over the past four decades are identified. The results revealed a degree of heterogeneity of the study region response to the ongoing global climate change, identified isolated areas, and quantified the warming rate in these areas. It is shown that in the west of the region, the SST trends are much higher than in the east, and in the warm season, they are about twice higher than in the cold season. Changes in water temperature and heat content anomalies in the water column of different regions are extremely uneven. The phases of alternating warm and cold periods are consistent with trends in the characteristics of the atmospheric centers of action, climate indices, and different climatic parameters.

Atmospheric Centers of Action in the Northern and Southern Hemispheres: Features and Variability

Atmospheric Centers of Action in the Northern and Southern Hemispheres: Features and Variability

Manifestation of the 11-year solar cycle in the North Atlantic climate

Analysis of fluctuations in the climate of the North Atlantic associated with the 11-year solar cycle is done using empirical data of the sea level pressure (SLP) and sea surface temperature (SST) for 1870-2012 and data of the North Atlantic Oscillation (NAO) index and Central England temperature. Emphasis is placed on the regions of the Icelandic and Azores atmospheric centers of action (CA). Methods of multiple linear regression and cross-wavelet analysis are used. The analysis reveals decadal oscillations of the SLP lagging by ∼3 years relative to the sunspot number, in the area of the Azores CA in the winter and autumn seasons. SLP variations that are approximately in phase with the solar cycle are noted in autumn in the Icelandic CA. Solar-related SLP variations in the Icelandic CA in winter occur approximately in anti-phase with the variations in the Azores CA, at smaller lag behind the solar cycle. SLP variations associated with the solar cycle are comparable in amplitude to variations due to the El Nino–Southern Oscillation (ENSO) and the Atlantic Multidecadal Oscillation (AMO). SST variations associated with the solar cycle are also revealed. They are several times weaker than variations due to the AMO, but of the same order of magnitude as variations due to the ENSO. The relation of the NAO index to the solar cycle is alternating and experiences modulation with a period of about 50 years.

Point vortices dynamics on a rotating sphere and modeling of global atmospheric vortices interaction

It is shown that the hydrodynamics equations for a thin spherical liquid layer are satisfied by the stream function of a pair of antipodal point vortices (APVs), in contrast to the stream function of a single point vortex on a sphere with a background of a uniform opposite sign vorticity. A simple zero solution of the equation of the absolute vorticity conservation is used for bypassing the well-known nonlinear problem of a point vortices interaction with a regular vorticity field, and an exact solution for the APV dynamics problem on a rotating sphere is obtained. Due to this, a new stable stationary solution for the dynamics of APV is obtained, which can model the dynamics of the global vortex structures, such as atmospheric centers of action.

Projection and possible causes of summer precipitation in eastern China using self-organizing map

Self-organizing map (SOM) is used to simulate summer daily precipitation over the Yangtze–Huaihe river basin in Eastern China, including future projections. SOM shows good behaviors in terms of probability distribution of daily rainfall and spatial distribution of rainfall indices, as well as consistency of multi-model simulations. Under RCP4.5 Scenario, daily rainfall at most sites (63%) is projected to shift towards larger values. For the early 21st century (2016–2035), precipitation in the central basin increases, yet decreases occur over the middle reaches of the Yangtze River as well as a part of its southeast area. For the late 21st century (2081–2100), the mean precipitation and extreme indices experience an overall increase except for a few southeast stations. The total precipitation in the lower reaches of the Yangtze River and in its south area is projected to increase from 7% at 1.5 °C global warming to 11% at 2 °C, while the intensity enhancement is more significant in southern and western sites of the domain. A clustering allows to regroup all SOM nodes into four distinct regimes. Such regional synoptic regimes show remarkable stability for future climate. The overall intensification of precipitation in future climate is linked to the occurrence-frequency rise of a wet regime which brings longitudinally closer the South Asia High (eastward extended) and the Western Pacific Subtropical High (westward extended), as well as the reduction of a dry pattern which makes the two atmospheric centers of action move away from each other.

ЛЕДОВИТОСТЬ АРКТИЧЕСКИХ МОРЕЙ И ЕЁ СВЯЗЬ С ПРИЗЕМНОЙ ТЕМПЕРАТУРОЙ ВОЗДУХА В СЕВЕРНОМ ПОЛУШАРИИ

The linear relationship between average monthly anomalies of the ice coverage in the Arctic seas and the surface air temperature over the land in the Northern hemisphere in March and September was analyzed for the purpose of finding regions with statistically significant correlations. Possible mechanisms of the revealed interrelations are discussed. Data on the surface temperature and the ice concentration from Met Office Hadley Centre were used in this study. A negative correlation of the sea ice with the temperature in the land regions adjacent to the seas, as well as a number of remote relations was revealed. Specifically, statistically significant relations were found between anomalies of the ice area in the Laptev Sea in September with the temperature anomalies in the Mediterranean region, as well as with the temperature anomalies in Central Asia. In most cases, such relationships may be explained by the influence of atmospheric circulation, including the North Atlantic Oscillation, the Arctic Oscillation, the Pacific Decadal Oscillation, and variability in the intensity of the atmospheric centers of action. Characteristics of seasonal variations of the sea ice coverage and climatic trends together with variability and autocorrelation of the coverage anomalies are considered. The largest reduction in the ice area is observed for the recent decades in the Barents Sea in winter while in the Kara, Laptev and East Siberian seas - in summer.

Impact of Seasonal Low on Sea Level Rise

Every region around the globe has its unique climatic conditions which are set based on different orographic constant and atmospheric dynamic features. These features posses’ variability on different time scales. Determining the local sea level change based on terrestrial non-tidal, short-term variability is complicated. Some internal mechanisms of ocean are also taking place along with the external physical ones. We show that variability at Sindh-Baluchistan coastal belt can be greatly explained via dimensional indices of the position and intensity of the atmospheric center of action (COAs). This technique has already proved its usefulness at number of location especially in Northern Atlantic. It takes into account the changes in the atmospheric pressure which is exerted on the sea surface influencing the variability in sea level on seasonal scale and on inter-annual basis. As warming causes thermal expansion of water it also causes changes in atmospheric circulation. Both of these processes affect the sea level variability on their respective time scales. Atmospheric being the quicker one of the two to pass on the effect is also more influential to explain the variability in local sea level. In this attempt the COA approach is used to assess the impact of low pressure on local sea levels.

Characteristics and dynamics of wind-driven upwelling in the Alaskan Beaufort Sea based on six years of mooring data

Six years of mooring data from the Alaskan Beaufort Sea slope, together with meteorological observations and reanalysis fields, are used to quantify the occurrence of wind-driven upwelling and the associated atmospheric forcing. The canonical upwelling event, composited from 115 individual events, reveals that when the easterly wind is strongest the entire shelfbreak jet is reversed to the west. At the end of the event a bottom-intensified, eastward-flowing “rebound jet” spins up that is stronger than the normal shelfbreak jet. The cross-isobath flow has a three-layer structure with onshore flow in the surface layer, offshore flow in the middle of the water column, and onshore flow near the bottom. This is because the reversed shelfbreak jet is oriented slightly onshore which overwhelms the cross-isobath surface Ekman transport. The vertically-integrated along-isobath momentum balance supports this interpretation and indicates that the rebound jet is driven by the zonal gradient in sea surface height. During over two thirds of the events, Atlantic Water (AW) is upwelled to the shelfbreak, while for the remaining events only Pacific Water (PW) is upwelled. The primary driving factor behind this is the seasonal variation in the PW-AW interface depth offshore of the shelfbreak, which is controlled by the local wind stress curl. During summer, when PW-type events dominate, Ekman pumping associated with negative wind stress curl deepens the interface depth, limiting access to the Atlantic layer. Over the remainder of the year, when AW events dominate, Ekman suction associated with positive wind stress curl raises the interface. These variations are due to the influence of the two regional atmospheric centers of action — the Aleutian Low and the Beaufort High.

Long-term variations in surface air pressure and surface air temperature in the Northern Hemisphere mid-latitudes

The spatiotemporal variability of surface air pressure and surface air temperature in the Northern Hemisphere troposphere in 1990-2014 is described. In 2005 the low-frequency component (LFC) of average air temperature in January averaged over the latitude zone of 32.5°-67.5° N has stopped its increase that lasted for 35 years (from 1970). The LFC of air temperature in July has continued growing since 1975 (for 39 years). The anomalies of air pressure and air temperature for thirty-year periods and the dynamics of LFC of air temperature and air pressure in the atmospheric centers of action are analyzed.

Seasonal variation of the Beaufort shelfbreak jet and its relationship to Arctic cetacean occurrence

Using mooring time series from September 2008 to August 2012, together with ancillary atmospheric and satellite data sets, we quantify the seasonal variations of the shelfbreak jet in the Alaskan Beaufort Sea and explore connections to the occurrences of bowhead and beluga whales. Wind patterns during the 4 year study period are different from the long-term climatological conditions that the springtime peak in easterly winds shifted from May to June and the autumn peak was limited to October instead of extending farther into the fall. These changes were primarily due to the behavior of the two regional atmospheric centers of action, the Aleutian Low and Beaufort High. The volume transport of the shelfbreak jet, which peaks in the summer, was decomposed into a background (weak wind) component and a wind-driven component. The wind-driven component is correlated to the Pt. Barrow, AK alongcoast wind speed record although a more accurate prediction is obtained when considering the ice thickness at the mooring site. An upwelling index reveals that wind-driven upwelling is enhanced in June and October when storms are stronger and longer-lasting. The seasonal variation of Arctic cetacean occurrence is dominated by the eastward migration in spring, dictated by pack-ice patterns, and westward migration in fall, coincident with the autumn peak in shelfbreak upwelling intensity.

Synoptic-scale circulation patterns during summer derived from tree rings in mid-latitude Asia

Understanding past and recent climate and atmospheric circulation variability is vital for regions that are affected by climate extremes. In mid-latitude Asia, however, the synoptic climatology is complex and not yet fully understood. The aim of this study was to investigate dominant synoptic-scale circulation patterns during the summer season using a multi-species tree-ring width (TRW) network comprising 78 sites from mid-latitude Asia. For each TRW chronology, we calculated an atmospheric circulation tree-ring index (ACTI), based on 1000 hPa geopotential height data, to directly link tree growth to 13 summertime weather types and their associated local climate conditions for the period 1871–1993. Using the ACTI, three groups of similarly responding tree-ring sites can be associated with distinct large-scale atmospheric circulation patterns: 1. growth of drought sensitive trees is positively affected by a cyclone over northern Russia; 2. temperature sensitive trees show positive associations to a cyclone over northwestern Russia and an anticyclone over Mongolia; 3. trees at two high elevation sites show positive relations to a zonal cyclone extending from mid-latitude Eurasia to the West Pacific. The identified synoptic-scale circulation patterns showed spatiotemporal variability in their intensity and position, causing temporally varying climate conditions in mid-latitude Asia. Our results highlight that for regions with less pronounced atmospheric action centers during summer such as the occurrence of large-scale cyclones and anticyclones, synoptic-scale circulation patterns can be extracted and linked to the Northern Hemisphere circulation system. Thus, we provide a new and solid envelope for climate studies covering the past to the future.

Circulation anomalies in the atmospheric centers of action during the Eastern Pacific and Central Pacific El Niño

Based on the statistical analysis the teleconnections between circulation anomalies in the atmospheric centers of action and sea surface temperature anomalies are revealed for two types of El Nino. It is demonstrated that for the Eastern Pacific El Nino stronger teleconnections are registered in the Northern Hemisphere whereas the response to the Central Pacific El Nino is much stronger in the Southern Hemisphere. The Central Pacific El Nino is characterized by the more rapid signal propagation from the tropical zone to distant regions. In some cases the pattern of interaction with the atmospheric circulation considerably differs for two types of El Nino that defines differences in the fields of weather anomalies.

An assessment of the atmospheric centers of action in the northern hemisphere winter

In the northern hemisphere, there are six permanent or semi-permanent atmospheric activity centers, namely the Icelandic Low, Aleutian Low, India Low, Mongolia High, North Pacific High, and North Atlantic High. The first four are semi-permanent action centers and the last two are permanent circulation systems. The India Low exists only during the summer. By using 160 years (1850–2009) of monthly mean sea level pressure data from the Hadley Centre in the UK, we conduct a comprehensive study of the five boreal winter atmospheric centers of action (ACAs). Based on a unified definition and a method determined in previous studies, we calculate the indices of areal coverage (S), intensity (P), and position of action center (λ c, φ c) for each of these five ACAs. Through an in-depth analysis of these indices and their relationships with climate variables, we evaluate the indices by describing and explaining areal climate anomalies, particularly precipitation and temperature anomalies in China. We show that (1) ACAs significantly influence the climate anomalies of surrounding areas (2) the influences of oceanic ACAs are larger and the intensity anomalies of ACAs have a greater impact than their location displacement, and (3) ACAs exert more control on temperature than they do on precipitation. For the two ACAs over the north Atlantic, the impacts of their intensities on the anomalies of temperature and precipitation are similar. For the two ACAs over the north Pacific, their influences are almost the opposite. The most influential ACA for climate anomalies in China during the boreal winter is HMO. When HMO is stronger, China has a colder winter and it is wetter in the north. With stronger ACAs in the upstream, i.e., the Icelandic Low and North Atlantic High, northern China has a warmer winter. The ACAs over the north Pacific exert little influence on climate anomalies in China during winter. The analyses presented in this paper provide a set of useful indices for defining and describing ACAs, and they suggest insightful applications for these indices.

Estimating the trends and variability of atmospheric action centers over the Asian-Pacific region in summer in 1950–1979 and 1980–2012

The trend significance and the residual variability of integral atmospheric characteristics in the atmospheric action centers in the Asian-Pacific region in summer in 1950-1979 and 1980-2012 are computed. Basic differences are revealed between trends in circulation and residual variability in the atmo spheric action centers in the surface pressure field and in the field of geopotential H500 for these time periods. Increase in significant trends for the whole period and decrease in residual variability were found in the area of the Asian low in 1980-2012. A significant trend was observed in June and September in the area of the Hawaiian high. The summer Far Eastern low has intensified in recent years. The Okhotsk high strengthened in May and weakened in June, August, and September in the 2000s.

Interannual Seesaw between the Somali and the Australian Cross-Equatorial Flows and its Connection to the East Asian Summer Monsoon

Abstract The correlations among the summer, low-level, cross-equatorial flows (CEFs) over the Indian–west Pacific Ocean region on the interannual time scale are investigated by using both the NCEP–NCAR reanalysis and 40-yr ECMWF Re-Analysis (ERA-40) datasets. A significant negative correlation (seesaw) has been illustrated between the Somali CEF and the three CEFs north of Australia (the South China Sea, Celebes Sea, and New Guinea; they are referred to in combination as the Australian CEF). A seesaw index is thus defined with a higher (lower) value representing an intensified (weakened) Somali CEF but a weakened (intensified) Australian CEF. The connection of the seesaw with the East Asian summer monsoon (EASM) is then investigated. The results suggest that an enhanced seesaw corresponds to an intensified EASM with more rainfall in north China, the Yellow River valley, and the upper reach of the Yangtze River. The seesaw reflects the opposite covariability between the two atmospheric action centers in the Southern Hemisphere, Mascarene subtropical high, and Australian subtropical high. Whether the seesaw–EASM connection is influenced by El Niño–Southern Oscillation (ENSO) or the Indian Ocean SST dipole mode (IOD) is analyzed. The results remain unchanged when the ENSO- or IOD-related signals are excluded, although ENSO exerts a significant influence. This implies an additional predictability for the EASM from the CEF seesaw.