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1.
Kuwait was exposed to a severe dust storm on 19 March 2003, the eve of operation ??Iraqi Freedom??. Three days of dust events (19, 26, 27 March) were analyzed for their aerosol optical and physical properties using ground-based and satellite-retrieved measurements. Ground-based measurements of aerosol optical depth (or thickness; AOD or AOT) at 675?nm, ?? 657, ?ngstrom coefficient ?? 936/657, particulate matter of diameter 10???m or less, PM10 (??g/m3), and meteorological parameters were analyzed for March 2003. AOT exceeded 3 for the 3?days of interest and PM10 concentrations reached as high value as 2,457???g/m3 on 19 March dust storm day. Retrieved aerosol characteristics from space using Moderate Resolution Imaging Spectrometer (MODIS) on board Terra and Aqua satellite were examined against ground-based measurements. A strong correlation was found between ground-based measurements of ?? 675 and the Terra-MODIS retrieved AOD550. The synoptic of the dust storm were analyzed and source regions were identified using back trajectory analysis and Total Ozone Mapping Spectrometer Aerosol Index.  相似文献   

2.
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3.
Spatial distribution and trends in mean and absolute maximum and minimum temperatures and in the diurnal temperature range were analysed at 47 stations in the eastern Baltic region (Lithuania, Latvia and Estonia) during 1951–2010. Dependence of the studied variables on geographical factors (latitude, the Baltic Sea, land elevation) is discussed. Statistically significant increasing trends in maximum and minimum temperatures were detected for March, April, July, August and annual values. At the majority of stations, the increase was detected also in February and May in case of maximum temperature and in January and May in case of minimum temperature. Warming was slightly higher in the northern part of the study area, i.e. in Estonia. Trends in the diurnal temperature range differ seasonally. The highest increasing trend revealed in April and, at some stations, also in May, July and August. Negative and mostly insignificant changes have occurred in January, February, March and June. The annual temperature range has not changed.  相似文献   

4.

This study provides an overview of the drought situation in Northeast Brazil for the past, present, and future. Droughts affect more people than any other natural hazard owing to their large scale and long-lasting nature. They are recurrent in the region and while some measures have been taken by the governments to mitigate their impacts, there is still a perception that residents, mainly in rural areas, are not yet adapted to these hazards. The drought affecting the Northeast from 2012 to 2015, however, has had an intensity and impact not seen in several decades and has already destroyed large swaths of cropland, affecting hundreds of cities and towns across the region, and leaving ranchers struggling to feed and water cattle. Future climate projections for the area show large temperature increases and rainfall reductions, which, together with a tendency for longer periods with consecutive dry days, suggest the occurrence of more frequent/intense dry spells and droughts and a tendency toward aridification in the region. All these conditions lead to an increase in evaporation from reservoirs and lakes, affecting irrigation and agriculture as well as key water uses including hydropower and industry, and thus, the welfare of the residents. Integrating drought monitoring and seasonal forecasting provides efficient means of assessing impacts of climate variability and change, identifying vulnerabilities, and allowing for better adaptation measures not only for medium- and long-term climate change but also for extremes of the interannual climate variability, particularly droughts.

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5.
l. IntroductionPrevious studies have shown climatological and seasonal surface temperature and humld-ity dlstributlons over China (Wang and Gaffen, 200l ) and evaluated trends in seasonal meansof several surface humidity variables, rainfall, temperatures, and apparent temPerature for thelast half century (Easterling et al., 2000, Zhai et al., 1999, Zhai and Eskridge, l997, Zhai andRen, l997, Wang and Gaffen, 200l). However, trends in local temperatures, and particularlytrends in extreme he…  相似文献   

6.
Tree-ring width (TRW) and stable carbon isotope (??13C) in tree-ring cellulose of subalpine fir (Abies fabri) were used to develop high-resolution climate proxy data to indicate snow-depth variations in the Gongga Mountain, west China. Tree radial growth- and ??13C-climate response analyses demonstrated that the TRW and ??13C at the timberline (3,400?m.a.s.l.) are mainly influenced by temperature and precipitation of previous growth seasons and current summer (June to August) under cold and humid conditions. Considering the analogous control factors on both tree growth and carbon isotope discrimination (??13C) and snow accumulation, the negative and significant relationships between tree-ring parameters (TRW and ??13C) and mean monthly snowpack depth were found. Herein, by combining two tree-ring parameters, a primary snow-depth reconstruction (previous October to current May) over the reliable period A.D. 1880?C2004 was estimated. The reconstruction explains 58.0% of the variance in the instrumental record, and in particular captures the longer-term fluctuations successfully. Except the period with extreme higher snowpack depth around 1990, the snowpack depth seems to fluctuate in a normal way. The reconstruction agrees with the nearby snowpack depth record in Kangding and the mean observed snowpack-depth variations of the stations on the Tibetan Plateau, particularly at long-term scales. The snowpack depth in low-frequency fluctuations, during the past century, agrees quite well with the Eastern India precipitation covering the period of previous October?Ccurrent May. Our results suggest that combing tree-ring width and ??13C in certain subalpine tree species growing on the Tibetan Plateau may be an effective way for reconstructing regional snowpack variations.  相似文献   

7.
It is proposed that, land?Catmosphere interaction around the time of monsoon onset could modulate the first episode of climatological intraseasonal oscillation (CISO) and may generate significant ??internal?? interannual variation in the Indian summer monsoon rainfall. The regional climate model RegCM3 is used over Indian monsoon domain for 27?years of control simulation. In order to prove the hypothesis, another two sets of experiment are performed using two different boundary conditions (El Ni?o year and non-ENSO year). In each of these experiments, a single year of boundary conditions are used repeatedly year after year to generate ??internal?? interannual monsoon variability. Simulation of monsoon climate in the control model run is found to be in reasonably good agreement with observation. However, large rainfall bias is seen over Arabian Sea and Bay of Bengal. The interannual monsoon rainfall variability are of the same order in two experiments, which suggest that the external influences may not be important on the generation of ??internal?? monsoon rainfall variability. It is shown that, a dry (wet) pre-onset land-surface condition increases (decreases) rainfall in June which in turn leads to an anomalous increase (decrease) in seasonal (JJAS) rainfall. The phase and amplitude of CISO are modulated during May?CJune and beyond that the modulation of CISO is quite negligible. Though the pre-onset rainfall is unpredictable, significant modulation of the post-onset monsoon rainfall by it can be exploited to improve predictive skill within the monsoon season.  相似文献   

8.
A deep low in sea-level pressure is present from May to September over Pakistan and northwestern India (hereafter, the Pak?CIndia low). It is often referred as the ??heat?? low to convey the significance of surface thermal effects reckoned to be important for its origin. The present analysis, rooted in observations and diagnostic modeling, suggests that the Pak?CIndia low is influenced both by regional and remote forcing. Regionally, the influence of Hindu Kush mountains is found to be stronger than the impact of land-surface heating and attendant sensible heating of the planetary boundary layer, questioning the suitability of the ??heat?? label in canonical references to this circulation feature. Observational analysis indicates that the notable May-to-June deepening of the Pak?CIndia low and its further deepening in July, however, arises from remote forcing??the development of monsoon deep-convection over the Bay of Bengal and eastern India in June and July. It is hypothesized that the associated upstream descent over Iran?CTurkmenistan?CAfghanistan (i.e. east of the Caspian Sea) and related low-level northerlies over the Elburz?CZagros?CHindu Kush mountains contribute to the strengthening of the Pak?CIndia low in June (and July) from interaction with regional orography.  相似文献   

9.
The United Nations Environment Programme (UNEP) performed field surveys at 15 sites in Bosnia–Herzegovina where depleted uranium (DU) ammunition was used by the North Atlantic Treaty Organization (NATO) during the Balkans conflict (1994–1995). During the field missions, the Italian Environmental Protection Agency (APAT) evaluated airborne contamination due to DU dusts or aerosol particles, generated at the time of the conflict by the impact of DU ammunition on hard targets, using lichens and tree barks as biomonitors. Each sample was analyzed by alpha-spectrometry for DU determination. The 234U/238U activity concentration ratios were used to distinguish natural from anthropogenic uranium. This paper reports the data obtained by the UNEP investigation, including (non-radioactive) metal and other element concentrations in lichen and tree bark samples measured by instrumental neutron activation analysis (INAA). The results indicated: (i) lichens and tree barks are sensitive bio-accumulators of past airborne contamination by depleted uranium dusts; (ii) 8 years after the conflict, environmental DU contamination is still present at some of the target sites; and (iii) the highest concentrations of most non-radioactive elements were found at sites used for ammunition destruction.  相似文献   

10.
A seasonal cycle has been observed in the high and coarse resolution intra-annual analyses of oxygen isotopic composition (??18O) of teak (Tectona grandis) cellulose from southern India, that receives both the south-west (SW) (summer) and the north-east (NE) (winter, more depleted in 18O) monsoon rains. The seasonal cycle as recorded by teak, with an amplitude between 1 and 3??, shows lower ??18O values at the early and late growing seasons than at the middle. This pattern is opposite to that found in central Indian teak, nurtured mostly by the SW monsoon rain. A comparison of the observed and modeled intra-annual profiles reveals that the observed pattern of intra-annual ??18O variation in southern India is explainable only if teak trees had sampled rainfall from both the monsoons. Thus it appears possible to detect years of past excess NE monsoon rains by analyzing the ??18O of cellulose from the latewood of teak trees growing in Kerala, southern India.  相似文献   

11.
For the first time a simulation of blowing snow events was validated in detail using one-month long observations (January 2010) made in Adélie Land, Antarctica. A regional climate model featuring a coupled atmosphere/blowing snow/snowpack model is forced laterally by meteorological re-analyses. The vertical grid spacing was 2 m from 2 to 20 m above the surface and the horizontal grid spacing was 5?km. The simulation was validated by comparing the occurrence of blowing snow events and other meteorological parameters at two automatic weather stations. The Nash test allowed us to compute efficiencies of the simulation. The regional climate model simulated the observed wind speed with a positive efficiency (0.69). Wind speeds higher than 12 m s ?1 were underestimated. Positive efficiency of the simulated wind speed was a prerequisite for validating the blowing snow model. Temperatures were simulated with a slightly negative efficiency (?0.16) due to overestimation of the amplitude of the diurnal cycle during one week, probably because the cloud cover was underestimated at that location during the period concerned. Snowfall events were correctly simulated by our model, as confirmed by field reports. Because observations suggested that our instrument (an acoustic sounder) tends to overestimate the blowing snow flux, data were not sufficiently accurate to allow the complete validation of snow drift values. However, the simulation of blowing snow occurrence was in good agreement with the observations made during the first 20 days of January 2010, despite the fact that the blowing snow flux may be underestimated by the regional climate model during pure blowing snow events. We found that blowing snow occurs in Adélie Land only when the 30-min wind speed value at 2 m a.g.l. is >10 m s ?1. The validation for the last 10 days of January 2010 was less satisfactory because of complications introduced by surface melting and refreezing.  相似文献   

12.
1 Physical and Chemical Structural Characteristics of Urban ABLObtained preliminarily the atmospheric dynamic structure of the urban ABL: Urban heat island and urban wind, the zero-plane displacement and roughness of urban building blocks, the distribution and dynamic and thermal impacts of urban fog. In the aspect of city-scale simulation research, the effect of the topography around the outskirts of Beijing on the urban wind field and the effect of buildings on the urban atmospheric circulation are studied. The possible influencing mechanisms of the U-shaped mountains to the west and north of Beijing on the daily variation of the urban wind field, and the formation, transport and cumulation of urban pollutants are analyzed and some distribution charts are obtained.  相似文献   

13.
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14.
Increasingly severe drought has not only threatened food security but also resulted in massive socio-economic losses. In the face of increasingly serious drought conditions, the question of how to mitigate its impacts through appropriate measures has received great attention. The overall goal of this study is to examine the influence of policies and social capital on farmers’ decisions to adopt adaptation measures against drought. The study is based on a large-scale household and village survey conducted in six provinces nationwide. The survey results show that 86% of rural households have taken adaptive measures to protect crop production against drought, most of which are non-engineering measures. In the case of non-engineering measures, changing agricultural production inputs and adjusting seeding or harvesting dates are two popular options. A multivariate regression analysis reveals that government policy support against drought such as releasing early warning information and post-disaster services, technical assistance, financial and physical supports have significantly improved farmers’ ability to adapt to drought. However, since only 5% of villages benefited from such supports, the government in China still has significant room to implement these assistances. Moreover, having a higher level of social capital in a farm household significantly increases their adaptation capacity against drought. Therefore, the government should pay particular attention to the farming communities, and farmers within a community who have a low level of social capital. Finally, farmers’ ability to adapt to drought is also associated with the characteristics of their households and local communities. The results of this study also have implications for national adaptation plans for agriculture under climate change in other developing countries.  相似文献   

15.
薛纪善  刘艳 《大气科学进展》2007,24(6):1099-1108
This paper summarizes the recent progress of numerical weather prediction(NWP)research since the last review was published.The new generation NWP system named GRAPES(the Global and Regional Assimila- tion and Prediction System),which consists of variational or sequential data assimilation and nonhydrostatic prediction model with options of configuration for either global or regional domains,is briefly introduced, with stress on their scientific design and preliminary results during pre-operational implementation.In ad- dition to the development of GRAPES,the achievements in new methodologies of data assimilation,new improvements of model physics such as parameterization of clouds and planetary boundary layer,mesoscale ensemble prediction system and numerical prediction of air quality are presented.The scientific issues which should be emphasized for the future are discussed finally.  相似文献   

16.
Perceptions of a continuing crisis in managing Sahelian resources are rooted in five dimensions of the Sahel Drought of 1972–1974 as it was understood at the time: crises in rainfall (drought), food supply, livestock management, environmental degradation, and household coping capabilities. A closer examination of household livelihood and farming systems shows that adaptive strategies have been evolved in response to each of these imperatives. Illustrations are provided from recent research in north–east Nigeria. A systematic understanding of indigenous adaptive capabilities can provide a basis for policies enabling a reduction of dependency on aid assistance in the Sahel.  相似文献   

17.
Trends and periodicity analyses can provide information on climate variability inherent in a particular variable. In this study, trend tests and spectral analysis are used to examine the existence of trends and cycles in temperature series (1901–2000) of Nigeria. Periods 1901–1929 and 1942–1980 exhibited cooling trends while 1930–1941 and 1981–2000 showed warming trends. The warmest years in Nigeria were 1941, 1935, 1931 and 1987. The coldest years were 1929, 1975, 1925 and 1974. Whereas no significant trends were detected for 1901–1930 period, the standard period 1931–1960 was marked by significant cooling while 1961–1990 was marked with significant warming. Annual temperature has risen by 0.03?°C/decade during the last century. The overall warming was mostly confined to the south of 12°N especially during April and June. Changes in minimum temperature are higher than that of maximum temperature. The quasi-biennial oscillation was found in annual data for all the six zones with periods of about 2–4?years. Nigeria landscape is under strong North Atlantic Oscillation influence in dry season and under ENSO influence during wet season. Annual temperature series was also found to exhibit significant negative correlation with SOI.  相似文献   

18.
In contrast to previous studies that have tended to focus on the influence of the total Arctic sea-ice cover on the East Asian summer tripole rainfall pattern, the present study identifies the Barents Sea as the key region where the June sea-ice variability exerts the most significant impacts on the East Asian August tripole rainfall pattern, and explores the teleconnection mechanisms involved. The results reveal that a reduction in June sea ice excites anomalous upward air motion due to strong near-surface thermal forcing, which further triggers a meridional overturning wave-like pattern extending to midlatitudes.Anomalous downward motion therefore forms over the Caspian Sea, which in turn induces zonally oriented overturning circulation along the subtropical jet stream, exhibiting the east–west Rossby wave train known as the Silk Road pattern. It is suggested that the Bonin high, a subtropical anticyclone predominant near South Korea, shows a significant anomaly due to the eastward extension of the Silk Road pattern to East Asia. As a possible descending branch of the Hadley cell, the Bonin high anomaly ultimately triggers a meridional overturning, establishing the Pacific–Japan pattern. This in turn induces an anomalous anticyclone and cyclone pair over East Asia, and a tripole vertical convection anomaly meridionally oriented over East Asia. Consequently, a tripole rainfall anomaly pattern is observed over East Asia. Results from numerical experiments using version 5 of the Community Atmosphere Model support the interpretation of this chain of events.  相似文献   

19.
Wavelet analysis is used to study the interannual and interdecadal variations of rainfall in China and atmospheric circulation factors, including the key atmospheric oscillations, W, C, E patterns and subtropical high. Regression analysis and correlation analysis are both used to study the relationship of atmospheric circulation factors and China rainfall on different time scale and spatial scale. The results are as follows: (1) The variations of atmospheric circulation and rainfall in China are characterized by interannual and interdecadal scales. The variations of atmospheric circulation and rainfall are composed of interannual and interdecadal variations. It is necessary to separate those two time scales when climate changes and forecast are studied. (2) The variations of China rainfall are due to the interaction of multi-factors rather than single factors. The marked factors which influence the interannual and interdecadal variations are various. Subtropical high is one of the marked factors which influence interannual variations of rainfall, while AO, NAO, and NPO are one of the marked factors which influence interdecadal variations of rainfall. (3) The longer the time scale is, and the larger the spatial scale is, and the more remarkable the relationships between atmospheric circulation and rainfall are.  相似文献   

20.
The Chinook salmon (Oncorhynchus tshawytscha) spawns and rears in the cold, freshwater rivers and tributaries of California’s Central Valley, with four separate seasonal runs including fall and late-fall runs, a winter run, and a spring run. Dams and reservoirs have blocked access to most of the Chinook’s ancestral spawning areas in the upper reaches and tributaries. Consequently, the fish rely on the mainstem of the Sacramento River for spawning habitat. Future climatic warming could lead to alterations of the river’s temperature regime, which could further reduce the already fragmented Chinook habitat. Specifically, increased water temperatures could result in spawning and rearing temperature exceedences, thereby jeopardizing productivity, particularly in drought years. Paradoxically, water management plays a key role in potential adaptation options by maintaining spawning and rearing habitat now and in the future, as reservoirs such as Shasta provide a cold water supply that will be increasingly needed to counter the effects of climate change. Results suggest that the available cold pool behind Shasta could be maintained throughout the summer assuming median projections of mid-21st century warming of 2°C, but the maintenance of the cold pool with warming on the order of 4°C could be very challenging. The winter and spring runs are shown to be most at risk because of the timing of their reproduction.  相似文献   

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