Development Of Anticyclone Research Articles

Interannual variations of westward extension area of western Pacific subtropical high and its relationship with precipitation in East Asia

The western Pacific subtropical high (WPSH) is viewed as an important part of the East Asian summer monsoon system and its western boundary location significantly affects regional weather and climate. Based on characteristics of the WPSH western boundary in boreal summer, this study proposes a new index of WPSH, the westward extension area (WEA) index, defined as the area enclosed by the 587 dagpm contour in the region (10°–50°N, 105°–130°E), which can reasonably describe the area variations of WPSH when approaching and landing coastal regions. Compared with the canonical area index of WPSH, the WEA index can more effectively represent the WPSH-associated atmospheric circulation, water vapor transport, and convective activities in the boreal-summer East Asia-northwestern Pacific. A big WEA index significantly indicates flood in the middle reaches of Yangtze River basin and drought in South China. The WEA of WPSH has a significant connection with precipitation in Maritime Continent, due to the convection-circulation interaction in Philippine Sea. There, the WPSH-related sea surface temperature (SST) cooling and rainfall deficiency can excite Rossby waves, which induces the anomalous anticyclone development and the westward stretching and intensifying of WPSH that in turn further reduces rainfall in Philippine Sea. Moreover, the WEA index is significantly modulated by the preceding El Niño-type and tropical Indian Ocean SST anomalies, which may provide a highly predictable indicator of the continental precipitation in East Asia.

The oscillatory effect of chemical constituents, dynamics, barometric, and thermodynamics on weather over Accra, and Bissau

A sharp contrast in atmospheric weather conditions prevailed over Accra and Bissau and that led to the oscillatory nature of weather conditions between the two cities. During the latter part of July 2022, Bissau experienced persistent and continuous rains whilst Accra remained fair and dry. It was realized that when an air parcel rises, low-pressure system is created at the surface but when the air parcel sinks, high pressure forms. Pressures were predominantly high over Accra and low over Bissau during that time. Models from CAMS were used to study chemical compositions to determine the concentration and effect of Sulphur Dioxide (SO2) over the two cities. Wind behavior over various levels in the atmosphere was considered using model products from ECMWF, satellite imagery from EUMETSAT, and t-phi gram from the Air Resources Laboratory of NOAA to study the thermodynamics of the skies. METAR, hourly observations made by the National Meteorological Offices from the two cities were retrieved from the AADS and Ogimet to study the barometric nature during the period. Results show that the atmosphere over Bissau had been less polluted as compared to that of Accra which makes Bissau to be persistently cloudy. Atmospheric chemical constituents would have to compete for moisture if the concentration is high and does not support the sustenance of massive clouds capable of producing rain. It has been realized that the development of anticyclone, an anticlockwise circulation at the 200 hPa level contributed to the cloud sustenance over Bissau during that time.

Catabatic Winds in Oraviţa Depression (Romania). Case Studies

Abstract In some situations, field positioning of air pressure through development of anticyclone in the north - northeast of Romania and a cyclone in the south-west, create conditions favoring intensifying dynamics of air masses in Oraviţa Depression area. This phenomenon generates a catabatic wind which is known local as Coşava. Mode of expression is as strong intensification of the burst, which gives rise to considerable material damages. This study takes into account the analysis of three cases considered by us to be representative.

A climatological analysis of the incidence of brown haze in Auckland, New Zealand

ABSTRACTBrown haze has been observed over a number of urban centres in different geographical locations around the world. It is a clear indication of degradation in air quality above a city; however, little is known about its underlying causes. This study examines the incidence of brown haze over the subtropical city of Auckland, New Zealand between 2001 and 2011. Using photographs to document the incidence and severity of the haze and a combination of near‐surface meteorological observations, reanalysis data and three‐dimensional modelling approaches, a detailed climatology of the incidence of haze is developed. The results show that haze is observed during weekday mornings in the cool months, most commonly associated with cold, calm conditions. These conditions are most commonly prevalent with the slow eastward movement of anticyclones (classified as Kidson weather types H and HSE). However, the conditional probability of haze events occurring within these classes is less than 25%, and there is little consistency in the thresholds of surface meteorological conditions between classes. Re‐analysis of the mean sea‐level pressure at regional to synoptic scales reveals that the strength and stability of the anticyclone is important in determining the occurrence and severity of brown haze events. Brown haze development is associated with a strong NE‐SW temperature gradient immediately prior to the event, and anticyclonic development is enhanced by a well‐developed wave train across the Southern Ocean. Back trajectory modelling shows these conditions are associated with slow moving air masses and suggest that the source of pollution is most likely to be local in origin. The results demonstrate the importance of a detailed understanding of synoptic and regional scale meteorology in predicting urban scale pollution events, even when the source of the pollution is local.

Atmospheric pressure variations at extratropical latitudes associated with Forbush decreases of galactic cosmic rays

Changes of troposphere pressure associated with short-time variations of galactic cosmic rays (GCRs) taking place in the Northern hemisphere’s cold months (October–March) were analyzed for the period 1980–2006, NCEP/NCAR reanalysis data being used. Noticeable pressure variations during Forbush decreases of GCRs were revealed at extratropical latitudes of both hemispheres. The maxima of pressure increase were observed on the 3rd–4th days after the event onsets over Northern Europe and the European part of Russia in the Northern hemisphere, as well as on the 4th–5th days over the eastern part of the South Atlantic opposite Queen Maud Land and over the d’Urville Sea in the Southern Ocean. According to the weather chart analysis, the observed pressure growth, as a rule, results from the weakening of cyclones and intensification of anticyclone development in these areas. The presented results suggest that cosmic ray variations may influence the evolution of extratropical baric systems and play an important role in solar-terrestrial relationships.

The Late-Spring Maximum of Rainfall over the U.S. Central Plains and the Role of the Low-Level Jet

Abstract The seasonal rainfall over the U.S. central plains features a late-spring maximum. A spring–fall annual mode revealed from the empirical orthogonal function analysis on rainfall delineates a maximum center over the central plains that coincides with the large late-spring rainfall. This paper examines the large-scale dynamical and hydrological processes in forming the rainfall center. The NCEP–Department of Energy (DOE) reanalysis 2 data reveal that the baroclinic structure of the continental-scale circulation during late spring (May and June) induces a vertically out-of-phase divergent circulation forming strong convergence of water vapor flux over the central plains. Such circulation features generate concentrated convective activity in this region. The upper-level anticyclone development with the North American monsoon in July replaces the late-spring baroclinic structure and, in turn, reduces the convective activity. The Great Plains low-level jet (LLJ) plays a role in the downscaling process that connects the continental-scale circulation to rainfall. The LLJ coupled with approaching baroclinic waves leads to stronger moisture convergence in the central plains than that occurring under the upper-level anticyclone. The former type of the LLJ occurs most frequently in late spring and contributes to more than 60% of the rainfall. During midsummer (July and August), such a coupling is hindered by the well-developed upper-level anticyclone, subsequently decreasing the rainfall.

Planetary Wave Breaking and Tropospheric Forcing as Seen in the Stratospheric Sudden Warming of 2006

Abstract The major stratospheric sudden warming (SSW) of January 2006 is examined using meteorological fields from Goddard Earth Observing System version 4 (GEOS-4) analyses and forecast fields from the Navy Operational Global Atmospheric Prediction System–Advanced Level Physics, High Altitude (NOGAPS-ALPHA). The study focuses on the upper tropospheric forcing that led to the major SSW and the vertical structure of the subtropic wave breaking near 10 hPa that moved low tropical values of potential vorticity (PV) to the pole. Results show that an eastward-propagating upper tropospheric ridge over the North Atlantic with its associated cold temperature perturbations (as manifested by high 360-K potential temperature surface perturbations) and large positive local values of meridional heat flux directly forced a change in the stratospheric polar vortex, leading to the stratospheric subtropical wave breaking and warming. Results also show that the anticyclonic development, initiated by the subtropical wave breaking and associated with the poleward advection of the low PV values, occurred over a limited altitude range of approximately 6–10 km. The authors also show that the poleward advection of this localized low-PV anomaly was associated with changes in the Eliassen–Palm (EP) flux from equatorward to poleward, suggesting an important role for Rossby wave reflection in the SSW of January 2006. Similar upper tropospheric forcing and subtropical wave breaking were found to occur prior to the major SSW of January 2003.

Closed Anticyclones of the Subtropics and Midlatitudes: A 54-Yr Climatology (1950–2003) and Three Case Studies

Abstract The pioneering large-scale studies of cyclone frequency, location, and intensity conducted by Fred Sanders prompt similar questions about lesser-studied anticyclone development. The results of a climatology of closed anticyclones (CAs) at 200, 500, and 850 hPa, with an emphasis on the subtropics and midlatitudes, is presented to assess the seasonally varying distribution and hemispheric differences of these features. To construct the CA climatology, a counting program was applied to twice-daily 2.5° NCEP–NCAR reanalysis 200-, 500-, and 850-hPa geopotential height fields for the period 1950–2003. Stationary CAs, defined as those CAs that were located at a particular location for consecutive time periods, were counted only once. The climatology results show that 200-hPa CAs occur preferentially during summer over subtropical continental regions, while 500-hPa CAs occur preferentially over subtropical oceans in all seasons and over subtropical continents in summer. Conversely, 850-hPa CAs occur preferentially over oceanic regions beneath upper-level midocean troughs, and are most prominent in the Northern Hemisphere, and over midlatitude continents in winter. Three case studies of objectively identified CAs that produced heal waves over the United States, Europe, and Australia in 1995, 2003, and 2004, respectively, are presented to supplement the climatological results. The case studies, examining the subset of CAs than can produce heat waves, illustrate how climatologically hot continental tropical air masses produced over arid and semiarid regions of the subtropics and lower midlatitudes can become abnormally hot in conjunction with dynamically driven upper-level ridge amplification. Subsequently, these abnormally hot air masses are advected downstream away from their source regions in conjunction with transient disturbances embedded in anomalously strong westerly jets.

Mechanisms that influence the formation of high‐ozone regions in the boundary layer downwind of the Asian continent in winter and spring

The seasonal variation of ozone (O3) in the boundary layer (BL) over the western Pacific is investigated using a chemistry‐transport model. The model results for January and April–May 2002 were evaluated by comparison with PEACE aircraft observations. In January, strong northwesterlies efficiently transported NOx from the continent, leading to an O3 increase of approximately 5–10 ppbv over a distance of about 3000 km. In April, southwesterlies dominated due to anticyclone development over the western Pacific. Along this flow, O3 continued to be produced by NOx emitted from East Asia. This resulted in the formation of a high‐O3 (> 50 ppbv) region extending along the coastal areas of East Asia. This seasonal change in O3 was driven in part by a change in the net O3 production rate due to increases in solar UV and H2O. Its exact response depended on the NOx values in the BL. The net O3 production rate increased between winter and spring over the Asian continent and decreased over the remote western Pacific. Model simulations show that about 25% of the total O3 (of 10–20 ppbv) increase over the coastal region of Northeast Asia was due to local production from NOx emissions from China, and the rest was due to changes in background levels as well as emissions from Korea, Japan, and east Siberia. Uplift of BL air over Asia, horizontal transport in the free troposphere, and subsidence were the principal mechanisms of transporting Asian O3 to the central and eastern North Pacific.

A climatology of the Northern Hemisphere winter anticyclones

A climatology of the Northern Hemisphere winter anticyclonic activity is presented based on the European Centre for Medium‐Range Weather Forecasts reanalysis data set for the 1957–2002 period (ERA‐40) and a system‐centered method of tracking diagnostics. The method tracks the anticyclonic systems and monitors their evolution along their paths thus allowing documentation of aspects that have been previously overlooked due to the common perception of anticyclones as semi‐stationary, relatively uniform, slowly evolving structures. The anticyclonic signal is examined in a wide range of meteorological fields and at multiple levels, over the continental masses, over the subtropical ocean basins, and over the sectors where blocking highs tend to develop. Structural features, thermal and vorticity properties, and mobility characteristics of the corresponding anticyclones are highlighted. Over continental regions an association with low level pools of cold air is found to be prevalent for the Eurasian anticyclones but less so for the North American anticyclones. In the subtropical zone the anticyclonic signal in the regions affected by the winter monsoon, including southeastern Asia and the western Pacific features prominently in the upper levels. In the eastern sectors of the subtropical ocean basins the anticyclonic signal is less deep. Intense anticyclonic development at low levels is also identified over the western sectors of the subtropical continents where it appears associated to the effect of orography and of low level cooling. The dominant type of anticyclone observed in the regions of blocking is characterized by 5–6 days timescales and considerable eastward mobility.

South American Cold Surges: Types, Composites, and Case Studies

Abstract This paper examines the climatological, large-scale, and synoptic-scale aspects of South American cold surges using NCEP–NCAR gridded reanalyses for the 1992–96 period. Three common cold surge types are identified on the basis of a thickness (1000–850 hPa) criteria: type 1—a transient surge associated with weak anticyclone development east of the Andes in the absence of ridging aloft, type 2—a strong and persistent surge associated with dynamic anticyclogenesis aloft and strong surface anticyclone development east of the Andes, and type 3—a surge east of the Brazilian coastal mountains. Cold surges are most common during the winter and spring (Jun–Nov), accounting for 189 of the 256 events (74%). Case studies of two events (19–22 Jul 1992 and 12–14 Apr 1993) are conducted from both a conventional isobaric and a potential vorticity (PV) perspective. The upper-air flow pattern in the July 1992 type 2 case is characterized by the presence of a strong ridge–trough couplet, which amplifies and becomes...

A Study of the Influence of Satellite Data on GLA Analyses over the Atlantic Ocean during a Period of Blocking Anticyclone Development

This paper presents a statistical diagnosis of the differences between two Goddard Laboratory for Atmospheres analysis representations of temperature and wind speed, one containing satellite data influences (SAT analyses) and one without (NOSAT analyses), for a case of oceanic blocking anticyclone development. Results, obtained using area means and standard deviations of the two fields and correlation coefficients and root-mean-square differences between the two fields, indicate that the inclusion of satellite data can have significant impact on ocean-domain analyses. This is especially evident if one examines higher-order fields that represent gradients in the basic variable fields or contain covariances between two different variables (e.g., advections). More specifically, the inclusion of satellite data resulted in a cold (warm) temperature bias at low (high) levels and weaker temperature gradients, stronger winds, weaker vertical wind shears, and a warm-air advection bias at most levels. The SAT analyses also exhibited larger standard deviations than the NOSAT for wind speed, relative vorticity, vorticity advection, temperature advection, and 500-mb height tendencies, suggesting that for this case the spatial variability of the circulation features were enhanced by the inclusion of satellite data. Even so, since height tendencies forced by vorticity and temperature advection were less sensitive to the addition of satellite data than were the advection quantities themselves, the dynamics of the blocking system was apparently less influenced by the presence of satellite data than was the structure of the system.

Rapid 500-mb Cyclogenesis and Anticyclogenesis

Rapid intensification of cyclones and anticyclones in National Meteorological Center 500-mb height analyses is investigated during the 1983–84 through 1986–87 cool seasons (September through May). Rapid intensification is defined by analyzed height decreases (increases) of at least 10(5) dam in 24 h at the centers of 500-mb cyclones (anticyclones), defined here by closed contours at 6-dam intervals around low (high) 500-mb heights. The threshold 24-h central height changes for rapidly intensifying 500-mb cyclones (anticyclones) are two standard deviations lower (higher) than the mean central height changes for all 500-mb cyclones (anticyclones) during the 1983–84 cool season. Rapid 500-mb cyclogenesis is climatologically preferred over the northwestern Pacific Ocean and northeastern North America, while anticyclogenesis is favored in high latitudes with little longitudinal preference, but with some concentration in frequency near Alaska and Greenland. Both phenomena are observed preferentially north of the 546-dam contour at 500 mb; thus, most rapidly intensifying cyclones (anticyclones) apparently are not (are) cut off from the 500-mb westerlies. On the average, rapidly intensifying 500-mb cyclones (anticyclones) are associated with intensifying surface cyclones (anticyclones). The surface cyclones associated with rapid 500-mb cyclogenesis are more likely to be rapidly developing than is expected climatologically. In a limited sample it is seen that, on the average, rapid 500-mb cyclone and anticyclone developments are underpredicted by operational forecast models. A case of nearly simultaneous 500-mb rapid cyclogenesis and anticyclogenesis over the Atlantic Ocean during, January 1985 is diagnosed with a quasi-geostrophic model. Neither system is cut off from the westerlies, and both are associated with rapidly intensifying surface counterparts. The 500-mb anticyclone in turn is preceded by (nearly rapid) surface cyclognesis upstream and evolves into a blocking pattern. The 500-mb height tendencies at the center of the rapidly intensifying 500-mb cyclone are forced primarily by lower-tropospheric cold air advection decreasing upward in magnitude beneath the system. On the other hand, the quasi-geostrophic tendencies underestimate those analyzed at the anticyclone center, suggesting the importance of non-quasi-geostrophic processes in rapid 500-mb anticyclone development.

Atmospheric circulation during the last ice age

The prevailing surface temperatures in summer and winter at several different stages of the last ice age, indicated at various points scattered over the Northern Hemisphere, by botanical, glaciological, marine biological, oceanographic, etc. evidence, are used to derive probable distributions of 1000−500 mbar thickness, roughly equivalent to mean temperature of the lowest 5 km of the atmosphere and indicating the general flow pattern of the atmosphere in depth. From these thermal wind patterns computation of the tendency to cyclonic and anticyclonic development is possible. Maps of this development field, taken together with the indicated steering of surface cyclones and anticyclones by the thermal winds, make it possible to sketch probable distributions of surface pressure (and, by implication, surface winds) prevailing during each of the glacial stages studied. New light is thrown on the onset of glaciation and on the regimes associated with the maximum extent of glaciation, with the Alleröd warm epoch and the Post-Alleröd cold stage when there was some readvance of the ice.

Geomagnetic Conditions and Anticyclonic Development *

The forecasting of development and movement of existing pressure systems are apparently the two outstanding problems of weather forecasting. This investigation was done with the belief that ordinary meteorological observation are not sufficient for an indication of the cause of development or movement of pressure systems and that other factors, probably solar, must be considered. Since geomagnetic changes are partly the result of solar radiation, geomagnetic observations were obtained and statistical tests were made of their relation to pressure system development. All such tests gave positive indications of a relation between the relative geomagnetic conditions of Tucson, Arizona and Cheltenham, Maryland and subsequent anticyclonic development over eastern United States.

Cyclonic and anticyclonic development

Cyclonic and anticyclonic development

Cyclonic and anticyclonic development

AbstractDevelopment of pressure systems involves horizontal divergence (positive or negative) approximately balanced by divergence of opposite sign in the upper troposphere, the total divergence integrated vertically and represented by the rate of change of surface pressure being a relatively small residual. It follows that a criterion for development is that there should be a significant difference between the lower and upper fields of divergence. Divergence is determined by the field of geostrophic departure or acceleration and it is shown that the difference between lower and upper divergence consists of two parts due respectively to shearing and to the development of thermal gradients. Rules concerning the distribution of surface divergence and convergence in different pressure and temperature distributions are inferred and a method of approaching the problem of forecasting on a three‐dimensional basis is put forward.