Maritime Tropical Air Research Articles

Drought Occurrence in Northern Nigeria: It’s Effects on the Developmental Efforts of the Sub-Region

The steady decline in the amount of rainfall in the Sahel caused by natural and anthropogenic factors and especially the equator-ward spread of the dry sub-tropical high pressure system in the sub-region that influences the moisture laden tropical maritime air mass to be restricted to the southern part of the country. And the drought condition is enhanced through over-cultivation, deforestation and over-grazing, thereby leaving the soil bare that aids the free movement of desert sand commonly noticed on the Northern sub-region of the country. This leads to serious repercussions on productive capacities and basic social services and to overcome this threat, hence the campaign for three planting, forestation, dam constructions and irrigation projects.

Flood risk analysis in the Taihu Basin during flood periods based on Copula function

太湖流域位于长江入海口，地处中国沿海经济带和长江沿线内陆经济带的交汇处，是中国高度城镇化地区之一.流域汛期降水受到多重天气系统的影响，不同的天气系统带来时空分布各异的降水，给该地区城镇防洪排涝工作造成了巨大的挑战.本文基于Copula理论对太湖流域汛期洪涝风险进行研究，考虑了因降水主导因素不同所造成的流域洪涝风险的时空差异性.在时间角度，采用降水主导因素发生时间的概率分布，将汛期划分为梅汛期和台汛期；在空间角度，通过Copula函数，对研究区进行聚类划分；在此基础上，根据太湖流域防洪规划，对流域梅汛期和台汛期的洪涝风险进行分析.研究结果表明：①太湖流域的汛期划分为：6月24日-7月21日为梅汛期，7月22日-9月22日为台汛期；②根据各分区降水和太湖水位的联合分布函数拟合效果的优劣，在梅汛期，太湖流域被划分为P-Ⅰ区、P-Ⅱ区和P-Ⅲ区；在台汛期，整个流域的降水作为一个整体，不分区；③到2025年，太湖流域在梅汛期和台汛期出现排涝不利情境的风险概率分别为2.4%和1.1%.本文的研究方法可以为太湖流域设计暴雨的调整、洪水资源的利用以及防洪排涝实时调度的决策提供科学参考.;The Taihu Basin is located at the estuary of the Yangtze River, belonging to the intersection of China coastal economic belt and the inland economic belt along the Yangtze River. It is one of China's highly urbanized areas. Under the influence of continental polar air masses, maritime tropical air masses and tropical cyclones, the types of precipitation in the Taihu Basin are divided into plum rain and typhoon rain. Different weather systems lead to the different heterogeneous precipitation, which brings great challenges to flood management in the basin. Taking the spatial and temporal differences of flood risk caused by different weather systems into consideration, this paper analyzed the flood risk based on Copula theory. In terms of time, the probability distribution of the precipitation dominant factors was used to divide the flood period into the plum rain period and the typhoon period. In terms of space, we clustered the study areas in the plum rain period and the typhoon period respectively by the Archimedean copula function. Finally, the flood disaster risk during the plum rain period and the typhoon period was analyzed. The results indicate that the flood period of the Taihu Basin is divided into the plum rain period (June 24 to July 21) and the typhoon period (July 22 to September 22). According to the joint distribution of sub-region precipitation and the Taihu Lake water level, the Taihu Basin is divided into three sub-regions (P-Ⅰ sub-region, P-Ⅱ sub-region and P-Ⅲ sub-region) in the plum rain period, while the Taihu Basin as a whole for flood risk analysis in the typhoon period. In the future, the probability of the drainage adverse in the Taihu Basin during the plum rain periods and the typhoon period is 2.4% and 1.1%, respectively. It is of great significance for the Taihu Basin to adjust the schemes of design storm and utilize flood resource and make the decision of real-time scheduling for flood control and drainage.

Twenty‐Five Years of Lower Tropospheric Ozone Observations in Tropical East Asia: The Influence of Emissions and Weather Patterns

AbstractTropospheric ozone affects the Earth's radiative balance, oxidative capacity, and air quality, yet the long‐term ozone trend in East Asia and its driver(s) remain poorly understood. Here we present ozone measurements obtained during 1994–2018 on China's southern coast. The measurement location intercepts China's outflow most of the time and the inflow of tropical maritime air during summer. We found an overall increase in the ozone level (0.35 ppbv/year), and the increase occurred mainly during the first half of the 25‐year period but appeared to level off in recent years in Chinese outflow. Large ozone increase (~20% per decade) was found in the maritime air. Model simulations show that recent weather conditions have reduced maritime ozone, counteracting the impact of the growing Southeast Asia's emissions. Our results fill the gap in the long‐term ozone trend in Asia and highlight the complex interaction of weather and emissions in driving the ozone change.

The Influence of Synoptic-Scale Air Mass Conditions on Seasonal Precipitation Patterns over North Carolina

This paper characterizes the influence of synoptic-scale air mass conditions on the spatial and temporal patterns of precipitation in North Carolina over a 16-year period (2003–2018). National Center for Environmental Prediction Stage IV multi-sensor precipitation estimates were used to describe seasonal variations in precipitation in the context of prevailing air mass conditions classified using the spatial synoptic classification system. Spatial analyses identified significant clustering of high daily precipitation amounts distributed along the east side of the Appalachian Mountains and along the Coastal Plains. Significant and heterogeneous clustering was prevalent in summer months and tended to coincide with land cover boundaries and complex terrain. The summer months were dominated by maritime tropical air mass conditions, whereas dry moderate air mass conditions prevailed in the winter, spring, and fall. Between the three geographic regions of North Carolina, the highest precipitation amounts were received in western North Carolina during the winter and spring, and in eastern North Carolina in the summer and fall. Central North Carolina received the least amount of precipitation; however, there was substantial variability between regions due to prevailing air mass conditions. There was an observed shift toward warmer and more humid air mass conditions in the winter, spring, and fall months throughout the study period (2003–2018), indicating a shift toward air mass conditions conducive to higher daily average rain rates in North Carolina.

STUDYING THE MOVEMENT OF THE INTER TROPICAL CONVERGENCE ZONE (ITCZ) OVER AFRICA INVERNAL EQUINOX

In this study, we have tried to study the movement of the Inter Tropical Convergence Zone (ITCZ) over Africa in April by analyzing Temperature, (U, V) Wind and rainfall, studying oscillation of the ITCZ and its relationship with temperature in the different seasons, within the range of Africa in a long period of time (statistical period of 60 years). This is the first long term (monthly, annually, and decadal) study of the ITCZ over Africa, In this study, not only the exact position of ITCZ over Africa is determined but also its position change in the period of 60 years, These results could be used in studying the impacts of ITCZ on climate variations due to changes of position and movement of ITCZ, over Africa also the direct impacts of this movement on sudden changes of seasons start and end of untimely rains. Through the study of the ITCZ movement over Africa in vernal equinox, we find that it is limited between latitudes 2o N to 18o N, and the speed and direction of wind coming from the Tropical Continental air mass (cT) masses in addition to temperature, as well speed and direction of wind coming from the Tropical Maritime air mass (mT) air masses, all of them effect on the movement of ITCZ to the north and south, in different decades, which led to displacement of rain belt over Africa from north to south and vice versa , in addition to change in the amount of Total rainfall over the Abyssinian Plateau during the different decades .

An Analysis of Air Masses Associated with Federal Ozone Exceedances Across St. Louis, Missouri: 2001–2010

The St. Louis, Missouri metropolitan region has a history of poor air quality. Although some studies have examined the surface and atmospheric conditions associated with federal ozone exceedances across St. Louis, little research has been done on the air mass types associated with ozone exceedances in this region. The research is a first step in that direction. Days with ozone exceedances from 2001 to 2010 were classified according to the accompanying air mass type that dominated the region on each of those days. This study found that over 70 percent of ozone exceedances occurred on days with maritime tropical air masses, and over 20 percent occurred on days with dry tropical masses. Exceedances also occurred with dry moderate air masses in the region. It is hoped that recognizing air masses associated with ozone exceedances will allow us to better alert the residents of these dangerous events.

On the Development of Spatial/Temporal Solar Radiation Maps: A Minas Gerais (Brazilian) Case Study

Appropriate information on solar resources is very important for a variety of technological areas, such as agriculture, meteorology, forestry engineering, and water resources, particularly for an innovative technology such as solar energy. In the market entry process of an innovative technology such as solar energy, the increased and sustained deployment of this energy technology strongly depends on the economy and reliability of the solar systems installed. The economy and reliability of a system are the consequences of a well-prepared project, resulting from an accurate knowledge of the solar resource available. Therefore, knowing the potential of the solar resource accurately is not only a need but also an imperative for the larger diffusion and use of the solar energy. The existing sources of the information on radiation in MG are quite varied, both at the institutional level and in different types of publications. The publications containing this information are project reports, internal reports of institutions, and several magazines. Thus, the quality of the data varies considerably, the information presents spatial and temporal discontinuity; moreover, the instruments and the measurement units are not standardised. The general objective of this paper is to recover, to qualify, to standardize, and to make available the best information from the current existing solar resource in MG, Brazil, either in the form of isoline charts of solar radiation or a numerical database. In this paper, the procedure to elaborate the maps of daily solar radiation and insolation, along with the monthly and annual averages, is described. We present one map with the localisation of the recording stations in addition to one annual and 12 monthly contour maps. The map of the daily global solar irradiation and the annual average determined in this project show that solar radiation on the state of Minas Gerais ranges from 4.5 to 6.5 kWh/m2. The maximum values occur in the northern region of Minas Gerais, and the minimum values occur in the southeast region, where there are areas of higher altitude (Mantiqueira and Serra do Caparaó) and the rainfall is more intense, with total annual rainfall greater than 1400 mm. The North and Northeast Regions of MG, where the largest annual irradiation of 6.5 kWh/m2 occurs, are characterised by a semiarid climate with annual rainfall between 600 - 800 mm and altitudes between 400 - 600 m. The maritime tropical air mass that acts between Brazil and Africa is the main climatic factor that inhibits cloud formation and, consequently, the rainfall in this region. Finally, the map of annual insolation reveals a consistent correlation between the daily rainfall and the solar radiation annual average.

Radar signatures of the urban effect on precipitation distribution: A case study for Atlanta, Georgia

Ground‐based weather radar from Peachtree City, GA, is used to examine the distribution of summer precipitation in northern Georgia, including metropolitan Atlanta, during June–August of 2002–2006. The study included 194 “synoptically benign” days with a maritime tropical air mass type. Areas in eastern metropolitan Atlanta are shown to have 30% more rainfall during these days than areas west of the city. Both precipitation amount and frequency were enhanced up to 80 km to the east of the urban core of Atlanta. A precipitation maxima northeast of Atlanta occurs near a precipitation anomaly and lightning flash density anomaly identified in previous studies. An hourly analysis of precipitation data demonstrates that the enhanced precipitation on the periphery of the urban core is most evident from 00–05 UTC (19‐00 LST). This study is the first to use ground‐based radar precipitation estimates in an attempt to quantify the impact of urbanization on precipitation.

Factors influencing new particle formation at the rural site, Harwell, United Kingdom

A study of large‐scale episodes of new particle formation observed at a rural site in southern England which is a receptor site for air masses with varying degrees of pollution is presented. Large‐scale episodes of new particle formation are infrequent at Harwell (26 episodes for 1999–2001; data capture of 55%), and it is shown that the most favorable situation for new particle formation in southern England is also infrequent. All episodes but three occurred when clean cool arctic or polar maritime air masses arrived in the UK bringing days of high solar radiation and thin cloud cover. The incursion of these cool air masses may be associated with passage of a cold front and leads to stronger winds and probably strong turbulent mixing; all favor new particle production. More exceptionally, nucleation occurred in warm polluted continental or tropical maritime air masses which shows that different conditions are also possible but much less probable. Higher concentrations of SO2 and higher relative humidity favor higher particle number in agreement with nucleation processes involving H2SO4 and H2O. Taken together, these parameters are insufficient to predict when a burst of particle formation due to nucleation will occur at Harwell, and other important variables must be influential.

Climatic controls on the stable isotopic composition of precipitation in Northeast Asia

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 23:137-148 (2003) - doi:10.3354/cr023137 Climatic controls on the stable isotopic composition of precipitation in Northeast Asia Kwang-Sik Lee1,*, Andrew J. Grundstein2, David B. Wenner3, Man-Sik Choi1, Nam-Chil Woo4, Dae-Ha Lee5 1Korea Basic Science Institute, Eoeun-dong 52, Yusung-gu, Daejeon 305-333, Korea 2Department of Geography, and 3Department of Geology, University of Georgia, Athens, Georgia 30602, USA 4Department of Earth System Sciences, Yonsei University, Seoul 120-749, Korea 5Korea Institute of Geoscience and Mineral Resources, Gajeong-dong 30, Yusung-gu, Daejeon 305-350, Korea *Email: kslee@kbsi.re.kr ABSTRACT: An examination of oxygen and hydrogen isotopic compositions of precipitation in NE Asia from the IAEA/WMO data set reveals that many sites have a distinct winter-summer seasonal pattern in deuterium excess (d-) values that appears to reflect different climatic conditions. To further understand this pattern, stable isotopic data were obtained for individual rainfall events over a 2 yr period at Jeju Island, Korea. The δ18O- and δD-values of precipitation at Jeju Island are not dependent upon temperature. However, the deuterium excess values, which range from 3.0 to 40.6‰, show a distinct seasonal variation with higher d-values in winter (>~15‰) and lower values in summer (~10‰). Such a seasonal variation is closely related to different air masses affecting the island during different seasons: a cold-dry continental polar air mass in winter and a hot-humid maritime tropical air mass in summer. KEY WORDS: Oxygen · Hydrogen · Isotopic composition · Precipitation · Deuterium excess values · Northeast Asia · Jeju Island · Korea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 23, No. 2. Online publication date: January 31, 2003 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2003 Inter-Research.

Continuous high‐frequency observations of hydrogen at the Mace Head baseline atmospheric monitoring station over the 1994–1998 period

Continuous high‐frequency (every 40‐min) automatic measurements of hydrogen have been made at the Mace Head atmospheric research station on the Atlantic Ocean coast of Ireland throughout 1994–1998. These observations represent one the most comprehensive in situ records of a trace gas that has received comparatively little attention. Individual measurements have been sorted by four independent methods to separate clean, maritime air masses from regionally polluted European air masses. Hydrogen concentrations in midlatitude Northern Hemisphere baseline air show a distinct seasonal cycle with highest concentrations during spring and lowest concentrations during late autumn, with a peak‐to‐trough amplitude of 38±6 ppb, averaged over the observed seasonal cycles from 1994 to 1998. The mean hydrogen concentration in midlatitude Northern Hemisphere baseline air on January 1, 1995, was estimated as 496.5 ppb with an upward trend of 1.2±0.8 ppb yr−1. Evidence has also been obtained for European pollution sources with source strength of about 0.8 Tg yr−1 and for deposition of hydrogen to soils. The observation of slightly elevated hydrogen concentrations relative to baseline levels in tropical maritime air masses points to a latitudinal gradient in hydrogen with higher concentrations in lower latitudes of the Northern Hemisphere and in the Southern Hemisphere. This is confirmed by comparable hydrogen observations at Cape Grim, Tasmania, which are consistently higher than measurements recorded at Mace Head. Mean hemispheric concentrations of 504 and 520 ppb have been estimated for the Northern and Southern Hemispheres, respectively, for January 1, 1996, corresponding to a total atmospheric hydrogen burden of 182 Tg.

The Cultural Diffusion of Rice Cropping in Cote d'Ivoire

Rice consumption and production have an ever-increasing impact on West African national economies and the changing local ecologies of the region. Cote d'Ivoire illustrates this point, with rising consumption, primarily in urban areas. Between 1984 and 1989 this rise cost an annual average of U.S.$93.7 million in imports, which increased to U.S.$107 million in 1993, making Cote d'Ivoire the largest importer in West Africa (FAO 1995). To meet this demand, large areas of moist lowlands and rain-fed uplands are being cleared for production. Rice is not a new crop to West Africa, and its cultivation has long been associated with a circumscribed rice zone. Today, as cultivation expands into new areas, farmers from various cultural backgrounds working in diverse ecologies adopt the crop to fit their particular needs and experiences. Its cultivation affects domestic and local economies and results in ecological change in ways that reflect the collective historical experience of the peoples who grow the rice. Many recent attempts to classify crop environments based on physical characteristics for the purpose of extending cultivation, such as Wim Andriesse and Louise Fresco's characterization of rice-growing environments in West Africa (1991), fail to consider the cultural and economic history of the crop and its diffusion. To do so examines a crop's potential only in a theoretical, laboratory-type physical setting devoid of cultural influence. Yet the human element in agriculture is anything but neutral: Crop distribution is not restricted to biogeographical patterns. In this article we combine the cultural history of cultivation in Cote d'Ivoire with the results of a field study of contemporary rice-cropping systems (Becker and Diallo 1992). based on data collected in interviews with farmers, local extension workers, and field observations in each of the fifty secondary administrative units, or departements, the country's cropping is divided into nine networks, or systems (Table I). Like Martin Lewis's regional agricultural geography in the Philippines (1992), these groupings are not territorially exclusive, although they mostly have a strong regional bond. Each takes into consideration the heterogeneous population of the country, where distinct systems of cropping are found side by side, often exploiting separate ecological niches and made up of sets of cropping technologies with their own histories. The approach is useful to development planners, especially when compared with the restricted biophysical focus so commonly used. An emphasis on networks addresses the production realities of farmers. No matter how many irrigation projects are built, farmers will only produce when it is in their best interest to do so. Beginning to recognize these self-interests is an essential step in efforts to improve agriculture. IVORIAN PHYSICAL AND HUMAN ENVIRONMENTS Cote d'Ivoire's physical landscape is underlain by Precambrian formations, dominated in the west by the granitic Mountains of Man, including 1,752-meter-high Mount Nimba at the point where Guinea, Liberia, and Cote d'Ivoire meet. Much of the landscape is undulating valley and upland, traversed by three major north - south-trending rivers - the Sassandra, the Bandama-Nzi, and the Comoe [ILLUSTRATION FOR FIGURE 1 OMITTED]. The climate is regulated by the relative positions of the tropical maritime air mass over the South Atlantic and the dry air associated with the North African anticyclone over the Sahara (Hayward and Oguntoyinbo 1987). The moist southwesterlies bring monsoon rains, with high rainfall totals (2,300 millimeters a year in Tabou). The longest rainy seasons are in the southwest, near the ocean, and in the mountains, along the border with Liberia and Guinea. But the dry Harmattan winds blow from the northeast, giving the Bouna Departement, bordering Burkina Faso (Upper Volta until 1984) and Ghana, low rainfall figures (less than 900 millimeters a year) (Atlas de Cote d'Ivoire 1979). …

Patterns of Holocene environmental change in the midwestern United States

Four pollen sequences along a transect from north-central Iowa to southeast Wisconsin reveal the distribution of prairie and forest during the Holocene and test the use of pollen isopolls in locating the Holocene prairie-forest border. Prairie was dominant in central Iowa and climate was drier than present from about 8000 to 3000 yr B.P. During the driest part of this period in central Iowa (6500-5500 yr B.P.), mesic forest prevailed in eastern Iowa and Wisconsin, suggesting conditions wetter than at present. Prairie replaced the mesic forest about 5400 yr B.P. in eastern Iowa but did not extend much farther east; mesic forests were replaced in southern Wisconsin and northern Illinois about 5400 yr B.P. by xeric oak forests. This change from mesic to xeric conditions at 5400 yr B.P. was widespread and suggests that the intrusion of drier Pacific air was blocked by maritime tropical air from the Gulf of Mexico until the late Holocene in this area.

Pluvial climatic episodes in North America and North Africa: types and correlation with global climate

Differences in Late Quaternary pluvial chronologies among the world's deserts can be related to fundamental differences in the climatology of those pluvial episodes. Paleoenvironmental records and climate model simulations for two Northern Hemisphere desert regions are used to illustrate two types of pluvial climatic regime. In the higher-latitude deserts of the American Southwest, pluvial conditions during the last glacial maximum were caused by the southward displacement of the westerly jet stream, in turn caused by the blocking effect of Laurentide Ice Sheet and a steepened arctic-equator pressure gradient. Winter seasonality of precipitation and substantially lower mean annual temperatures are reflected in the paleoenvironmental record, and simulated by models of 18,000 yr B.P. climate. A second pluvial climate type which strongly influences the lower-latitude deserts of North Africa is characterized by enhanced summer monsoons, and occurs during interglacials and, perhaps, interstadials. The primary forcing mechanism of the last pluvial episode in the Sahara and Libyan Deserts appears to have been increased solar radiation (Milankovitch forcing), causing thermally enhanced ocean-land pressure gradients and increased flow of maritime tropical air into the interior of the continent. Poleward displacement of the summer monsoon is consistent with floristic evidence for summer seasonality of precipitation, and replicated by model simulations of 9000 and 6000 yr B.P. climate. Chronologies from some deserts, such as the southern portion of the American Southwest, suggest the consecutive occurrence of both types of pluvial climatic regime. Pluvial conditions during the last glacial maximum were brought about by the equatorward displacement of the prevailing westerlies. A subsequent, more subdued pluvial period occurred later, between ∼ 12,500 and 8000 yr B.P., caused by the poleward displacement of summer monsoons. Characterization of the climatology of pluvial episodes generates explanations for their temporal distribution and, therefore, this approach may be useful in assessing the Quaternary chronology of pluvial episodes in other desert regions.

Meteorological conditions during the summer 1986 CITE 2 flight series

An overview of meteorological conditions during the NASA Global Tropospheric Experiment/Chemical Instrumentation Testing and Evaluation (GTE/CITE 2) summer 1986 flight series is presented. Computer‐generated isentropic trajectories are used to trace the history of air masses encountered along each aircraft flight path. The synoptic‐scale wind fields are depicted based upon Montgomery stream function analyses. Time series of aircraft‐measured temperature, dew point, ozone, and altitude are shown to depict air mass variability. Observed differences between maritime tropical and maritime polar air masses are discussed.

Late Quaternary vegetation and climate of southern Tierra del Fuego

Vegetation and climate over approximately the past 13,000 yr are reconstructed from fossil pollen in a 9.4-m mire section at Caleta Róbalo on Beagle Channel, Isla Navarino (54°56′S, 67°38′W), southern Tierra del Fuego. Fifty surface samples reflecting modern pollen dispersal serve to interpret the record. Chronologically controlled by nine radiocarbon dates, fossil pollen assemblages are: Empetrum-Gramineae- Gunnera-Tubuliflorae (zone 3b, 13,000–11,850 yr B.P.), Gramineae- Empetrum-assorted minor taxa (zone 3a, 11,850-10,000 yr B.P.), Nothofagus-Gramineae-Tubuliflorae-Polypodiaceae (zone 2, 10,000–5000 yr B.P.), Nothofagus-Empetrum (zone 1b, 5000-3000 yr B.P.), and Empetrum-Nothofagus (zone 1a, 3000-0 yr B.P.). Assemblages show tundra under a cold, dry climate (zone 3), followed by open woodland (zone 2), as conditions became warmer and less dry, and later, with greater humidity and lower temperatures, by closed forest and the spread of mires (zone 1). Comparisons drawn with records from Antarctica, New Zealand, Tasmania, and the subantarctic islands demonstrate broadly uniform conditions in the circumpolar Southern Hemisphere. The influences of continental and maritime antarctic air masses were apparently considerable in Tierra del Fuego during cold late-glacial time, whereas Holocene climate was largely regulated by interplay between maritime polar and maritime tropical air.

Erratum: The last pluvial climatic episodes in the deserts of southwestern North America

Long-term variations in the effective moisture of deserts are linked both to glacial–interglacial climatic cycles and, through the Milankovitch theory, to orbitally induced changes in solar radiation intensity1–4. For southwestern North America, comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late Wisconsin and early Holocene (23–8 kyr BP). Southward displacement of the Aleutian low-pressure centre and strengthened westerlies from ∼40° to 30° N were important features of the full-glacial (∼ 18 kyr BP) pluvial maximum. Increased cyclonic storms and weakened monsoons led to a winter precipitation regime, a feature seen both in the fossil record5,6 and climate models7,8. Dominantly zonal flow during this period contrasts with the latest Wisconsin and early Holocene (12–8 kyr BP), when meridional circulation transported maritime tropical air into the desert interior. We now show that plant macrofossil assemblages from packrat (Neotoma spp.) middens9 in the Mojave Desert provide evidence for increased temperatures and summer rainfall during this period10–12. The anomalously late persistence (to ∼8 kyr BP) of woodland in low-latitude, low-elevation deserts of the south-west13 is attributed to enhanced monsoonal circulation3.

Rural measurements of the chemical composition of airborne particles in the eastern United States

Quantitative measurements of particulate composition were made at three rural sites: in central South Dakota, on the Louisiana Gulf Coast, and in the Blue Ridge Mountains of Virginia. The first two sites were selected to determine background concentrations in continental polar and maritime tropical air masses, respectively, which affect the eastern United States during the summer. The Virginia site was selected as a receptor site, downwind of the midwestern source areas. The South Dakota data established the background concentrations. These concentrations were similar to the levels in Louisiana when air parcels arrived from the Gulf of Mexico, without recently passing over the United States. Levels of fine particles (diameters less than 2.5 μm) were highest in Virginia and were due chiefly to sulfate. Using trajectory and statistical analyses, it is shown that the residence time of an air parcel over the midwestern source area was the most important variable in determining the sulfate levels in the Blue Ridge Mountains.

停滞したリッジ西縁の亜熱帯レインバンド

The largeand meso-scale features of a subtropical rainband which caused thunderstorms over western Japan (-33N/130E) in 25-7 July 1981 are studied. This case aroused our interest because the convective activities persisted for about three days in the west side of a slowmoving ridge.Radar observations showed a persistent convective echo band of -800km length extending in NNW-SSE direction. This echo band was not accompanied with front-like strong thermal gradient. Satellite IR imageries showed that the rainband was a part of a long subtropical cloud zone formed along the northern periphery of the extremely moist tropical maritime airmass in the lower troposphere. The enhancement of cloud zone and the formation of the rainband was owing to the incessant feeding of moisture accompanied with the northward intrusion of the moist tropical maritime air along the western hem of the slow- moving ridge.Real data forecast experiments on the cloud zone and rainband were made using a coarseand a fine-mesh primitive equation model. While only the large-scale zone of weak precipitation relevant to the observed cloud zone was produced in the coarse-mesh (380kmmesh) model, the narrow rainband with low-level convergence was simulated in the finemesh (77km-mesh) model. The "dry experiment" (a experiment without condensation) did not produce any low-level convergence zone. This indicated influence of condensation process on the formation of this subtropical rainband.

CLOUD BAND MORPHOMETRY: AN ALTERNATIVE APPROACH TO SATELLITE IMAGE ANALYSIS

This research assesses the use of Cold Front Cloud Band (CFCB) morphometry as an indicator of the characteristics of air masses at cold fronts. Measurements of the configuration of the CFCB (i.e., length, width, length/width ratio, and radius of curvature) are made using GOES/SMS satellite imagery. CFCB height and air mass characteristics of temperature, specific humidity, 500 mb wind velocity, and 500 mb vorticity are derived from NWS surface and upper air charts. Nonparametric correlations are utilized to relate CFCB morphometric variables to the selected characteristics of maritime tropical (mT) and continental polar (cP) air masses as they meet to form cold fronts over the eastern United States. CFCB-Air Mass relationships resulting in higher correlations are examined through two series of interpretive tests. The stronger correlations imply a direct relationship between CFCB height and 500 mb vorticity and between CFCB length and cP specific humidity; and inverse relationships between both the CFCB le...