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1.
A large aerosol plume with optical depth exceeding 0.7 engulfs most parts of the Arabian Sea during the Asian summer monsoon season. Based on Micro Pulse Lidar observations during the June–September period of 2008 and 2009, the present study depicts, for the first time, the existence of an elevated dust layer occurring very frequently in the altitude band of 1–3.5 km over the west coast of peninsular India with relatively large values of linear depolarization ratio (δL). Large values of δL indicate the dominance of significantly non-spherical aerosols. The aerosol optical depth of this layer (0.2) is comparable to that of the entire atmospheric column during dust-free days. Back-trajectory analysis clearly shows the advection of airmass from the arid regions of Arabia and the west Arabian Sea, through the altitude region centered around 3 km. This is in contrast to the airmass below 1 km originating from the pristine Indian Ocean region which contains relatively spherical aerosols of marine origin with δL generally <0.05.  相似文献   

2.
The altitude profiles of particulate extinction in the upper troposphere and lower stratosphere (UTLS) obtained from SAGE-II in the latitude region 0–30°N over the Indian longitude sector (70–90°E) are used to study the latitudinal variation of its annual pattern in this region during the volcanically quiescent period of 1998–2003. The SAGE-II data is compared with the lidar measurements from Gadanki (13.5°N, 79.2°E) when the satellite had an overhead occultation pass over a small geographical grid centered at this location. The particulate optical depth (τp) in the UT region shows a general decrease with increase in latitude and a pronounced summer–winter contrast with relatively low values during winter and high values during summer. In general, these variations are in accordance with the latitudinal variation of convective available potential energy (CAPE) and thunderstorm activity, which are good representative indices of tropospheric convection. While the particulate extinction (and τp) in the 18–21 km (LS1) region is relatively low in the equatorial region up to 15°N, it shows an increase in the off-equatorial region, beyond 15°N. While the annual variation of τp in the LS1 region is almost insignificant near the equator, it is rather well pronounced in latitude region between 10 and 15°N with relatively high values during winter and low values during summer. Beyond 20°N, this shows a prominent peak during summer. At a higher altitude, the 21–30 km (LS2) region, the latitude variation of τp shows a different pattern with high values near the equator and low values in the off-equatorial region confirming the existence of a stratospheric aerosol reservoir. Low values of τp at lower regime (LS1) near the equator could be due to rapid transport of particulates from the near equatorial region to higher latitudes, while the equatorial high at upper regime (LS2) could be due to lofting and subsequent accumulation.  相似文献   

3.
UV-B solar irradiance and meteorological variables were measured at the C.I.B.A. site (Low Atmosphere Research Laboratory), University of Valladolid, Spain, between January 2003 and March 2006. Calculated Ångström turbidity and aerosol optical thickness values were evaluated from the direct downward irradiance, surface pressure, air temperature and relative humidity values. Monthly turbidity β values for an average year showed minimum values in winter and maximum values in summer. The obtained values are according to an aerosol standard atmosphere between mean and clean continental model. UV-B model calculations were performed using a radiative transfer tropospheric model, TUV 4.1a; measured and calculated UV-B irradiance values were compared in order to establish possible values of single scattering albedo. The results show that calculated single scattering albedo values are according to an aerosol standard atmosphere between mean and polluted continental model.  相似文献   

4.
The dual frequency SCINDA NovAtel GSV 4004B GPS receiver installed at the Ile-Ife (low-latitude station) has been in operation since December 2009. Data records for the year 2010 were processed to obtain Total Electron Content (TEC) and S 4 index. These were interpreted to analyze the ionospheric condition during low geomagnetic activity period (when Dst is from ?40 to 0 nT) and during geomagnetic storm events (with Dst about ?100 nT). Seasonal variations of the TEC and S 4 index were also investigated. The occurrence of scintillations is closely linked to the peak value of TEC during the daytime; this is very evident during the equinox months when TEC ≥ 30 TECu. When the maximum TEC value is below 30 TECu, as shown by most of the days in the summer months, the scintillation phenomenon does not occur. During geomagnetic storms, the daytime segment of the TEC plot experiences fluctuations (even bifurcations) in values with the peak TEC value of about 40 TECu. From the interpreted data, the occurrence of geomagnetic storm does not necessarily suggest an increase in the level of scintillations at a low-latitude region. Also, there is a remarkable difference between the IRI 2007 model and the observed TEC values, as the daytime TEC peak differs in magnitude and time of occurrence from the observed TEC.  相似文献   

5.
As part of the multinational Lake Owens Dust Experiment (LODE), we have studied the generation of dust storms on the south sand sheet of Owens (dry) Lake, California, an anthropogenically desiccated playa reported to be the single greatest source of particulate matter in North America. During March 1993, we performed an intensive field study including eight significant dust storms, building on our prior work (1978–1984) and preliminary studies (1991–1992). We studied sources and magnitude of coarse saltating particles, the meteorological conditions that allow them to become mobile across the flat playa of Owens (dry) Lake, and how the motion of saltating particles across different types of playa surfaces results in the generation of PM10 dusts (aerosol particles smaller than 10 μm aerodynamic diameter). Saltating grains of lacustrine sand and broken crust abrade and disaggregate the playa surface into fine aerosols, and the resulting PM10 concentrations recorded during major dust storms are among the highest ever recorded in North America. On 23 March 1993, we measured a 2 h concentration on the playa of 40 620 μg m−3, as far as we can determine the highest ambient PM10 value ever recorded in the U.S.A. Abrasion of salt-silt-clay crusts by saltation is shown to be responsible for all but a small part of one dust storm. The quantity ‘sand run’, saltating particle transport multiplied by wind run, is shown to be very closely correlated with dust aerosol concentration. Finally, we have established that on-lake bed studies are essential for quantitative prediction of dust events on the Owens (dry) Lake bed, despite the difficult conditions encountered.  相似文献   

6.
Advection of continental aerosols over to the Arabian Sea and Indian Ocean regions during winter (when the prevailing synoptic wind is north-easterly) has been studied by examining the spatial distribution of the near-surface aerosol mass concentration (MC). In the northern part of Arabian Sea and north of the inter-tropical convergence zone (ITCZ) MC is significantly larger than that in the southern side of ITCZ. A prominent high in MC is observed near the mid-Arabian Sea region ∼12° to 15°N. Associated with local convergences introduced by mesoscale weather systems, pockets of high MC are observed at different locations over the oceanic regions. Significantly low values of MC are observed in the ITCZ. Surface streamlines and wind patterns indicate advection of continental aerosols from the adjoining landmass over to the oceanic environment. Aerosol mass concentration in the far oceanic region is also influenced by in situ production of sea-spray aerosols, which depends on wind speed. The nature of advection of continental aerosols has been studied by separating the wind-induced component of MC and chemical nature of the aerosols. The spatial variation of the wind-independent component matches well with that of the non-sea-salt aerosols estimated from chemical composition.  相似文献   

7.
The equatorial ionosphere responses over Brazil to two intense magnetic storms that occurred during 2001 are investigated. The equatorial ionization anomaly (EIA) and variations in the zonal electric field and meridional winds at different storms phases are studied using data collected by digisondes and GPS receivers. The difference between the F layer peak density (foF2) at an equatorial and a low latitude sites was used to quantify the EIA; while the difference between the true heights (hF) at the equatorial and an off-equatorial site was used to calculate the magnetic meridional winds. The vertical drift was calculated as dhF/dt. The results show prompt penetration electric fields causing unusual early morning development of the EIA, and disturbed dynamo electric field producing significant modification in the F region parameters. Variations to different degrees in the vertical drift, the thermospheric meridional winds and the EIA developments were observed depending on the storm phases.  相似文献   

8.
Aerosol particle size distribution and chemical properties are important in studies related to human health and climate. The present study describes an analysis of aerosol mass loading, Aerosol Optical Depth (AOD), black carbon aerosol mass concentration and carbon monoxide over tropical urban region of Hyderabad, India, during March 2006, coinciding with active forest fires season over India. Aerosol optical depth, particulate matter mass loading and carbon monoxide were observed to be high on days with air mass coming from north of the study area. Spatial occurrence of forest fires was analysed using MODIS daytime data and DMSP-OLS nighttime data sets. Aerosol optical depth measured using Microtops-II sunphotometer correlated well with MODIS derived AOD values. Results of the study suggested that synoptic meteorological conditions play an important role in the observed aerosol properties over the study area during the forest fire season.  相似文献   

9.
Sensitivity analysis is crucial in assessing the impact of climatic variables on reference evapotranspiration estimations. The sensitivity of the standardized ASCE–Penman–Monteith evapotranspiration equation for daily estimations to climatic variables has not yet been studied in Spain. Andalusia is located in southern Spain where almost 1 million ha are irrigated under quite different conditions; it has a high inter‐annual variability in rainfall. In this study, sensitivity analyses for this equation were carried out for temperature, relative humidity, solar radiation and wind speed data from 87 automatic weather stations, including coastal and inland locations, from 1999 to 2006. Topography and Mediterranean climate characterize the heterogeneous landscape and vegetation of this region. Simulated random and systematic errors have been added to meteorological data to obtain ET0 deviations and sensitivity coefficients for different time periods. BIAS and SEE (standard error of estimate) have been used to evaluate the effect of both types of errors. The results showed a large degree of daily and seasonal variability, especially for temperature and relative humidity. In general, the effect on ET0 values of introduced random errors was larger than that of systematic errors. ET0 overestimations were produced using positive errors in temperature, solar radiation and wind speed data, while these errors in relative humidity resulted in ET0 underestimations. The sensitivity of ET0 to the same climatic variables showed significant differences among locations. The geographical distribution of sensitivity coefficients across this region was also studied. As an example, during spring months, ET0 equation was more sensitive to temperature in stations located along the Guadalquivir Valley. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

10.
2015年3月磁暴期间中国中低纬地区电离层变化分析   总被引：9，自引：0，他引：9       下载免费PDF全文
2015年3月17日爆发了本太阳活动周最大的地磁暴,Dst指数达到-233 nT.本文利用电离层测高仪f_。F_2和h_mF_2、北斗同步卫星(BDSGEO)TEC以及GPS电离层闪烁S4指数对此次磁暴期间中国中低纬地区(北京、武汉、邵阳和三亚)的电离层变化进行分析,并对此次磁暴所引发电离层暴的可能机制进行了探讨.磁暴期间,中低纬电离层暴整体表现为正相暴之后长时间强的负相暴.3月17日白天中纬正相暴为风场抬升电离层所致,而驼峰区及低纬地区正相暴由东向穿透电场所引起;3月18日白天长时间的强负相暴为西向扰动发电机电场和成分扰动所引起;3月17和18日夜间的负相暴可能是日落东向电场受到抑制以及赤道向风场对扩散的抑制导致驼峰向赤道压缩所致,同时被抑制的日落东向电场强度不足以触发产生赤道扩展F,导致低纬三亚和邵阳夜间电离层闪烁在磁暴期间受到完全抑制.这是我们首次基于北斗同步卫星TEC组网观测开展的电离层暴研究.  相似文献   

11.
The data of continuous observations of ELF emissions (polar chorus) at South Pole Antarctic observatory (Φ = ?74.02°) for 1997–1999 and during the superstrong magnetic storms of October and November 2003 are analyzed. It has been established that an increase in polar chorus is as a rule observed during the initial and recovery phases of a magnetic storm at positive values of the IMF vertical component (IMF B z > 0). Under such conditions, South Pole is located in the region of closed field lines. It has been found that the generation of polar chorus at South Pole abruptly ceases during the storm main phase after the IMF B z southward turning and beginning of an intense substorm in the nightside auroral zone, probably, because this observatory appears in the region of projection of the open magnetosphere due to the expansion of the polar cap.  相似文献   

12.
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13.
Determining surface precipitation phase is required to properly correct precipitation gage data for wind effects, to determine the hydrologic response to a precipitation event, and for hydrologic modeling when rain will be treated differently from snow. In this paper we present a comparison of several methods for determining precipitation phase using 12 years of hourly precipitation, weather and snow data from a long-term measurement site at Reynolds Mountain East (RME), a headwater catchment within the Reynolds Creek Experimental Watershed (RCEW), in the Owyhee Mountains of Idaho, USA. Methods are based on thresholds of (1) air temperature (Ta) at 0 °C, (2) dual Ta threshold, −1 to 3 °C, (3) dewpoint temperature (Td) at 0 °C, and (4) wet bulb temperature (Tw) at 0 °C. The comparison shows that at the RME Grove site, the dual threshold approach predicts too much snow, while Ta, Td and Tw are generally similar predicting equivalent snow volumes over the 12 year-period indicating that during storms the cloud level is at or close to the surface at this location. To scale up the evaluation of these methods we evaluate them across a 380 m elevation range in RCEW during a large mixed-phase storm event. The event began as snow at all elevations and over the course of 4 h transitioned to rain at the lowest through highest elevations. Using 15-minute measurements of precipitation, changes in snow depth (zs), Ta, Td and Tw, at seven sites through this elevation range, we found precipitation phase linked to the during-storm surface humidity. By measuring humidity along an elevation gradient during the storm we are able to track changes in Td to reliably estimate precipitation phase and effectively track the elevation of the rain/snow transition during the event.  相似文献   

14.
东亚地区矿物尘气溶胶直接辐射强迫的初步模拟研究   总被引：11，自引：0，他引：11       下载免费PDF全文
为研究东亚地区矿物尘气溶胶的直接辐射效应,在区域气候模式RegCM3中加入起尘方案、建立矿物尘气溶胶输送模式,并将其辐射过程加入区域气候模式的辐射方案.通过对2001年3月～2002年3月的模拟发现：中国西北和蒙古国年平均地表起尘率在1μg/(m2·s)以上,最大达到90μg/(m2·s)是东亚地区最主要的矿物尘气溶胶源地;东亚地区矿物尘气溶胶柱含量最大值达5g/m2,出现在塔克拉玛干沙漠和秦岭地区;气溶胶大气顶直接辐射强迫基本呈现大陆上为正、海洋上正负均有的分布特征,区域平均辐射强迫在春夏秋冬分别为108, 088, 037,040W/m2,短波辐射强迫在陆上为正、海上正负均有,长波辐射强迫均为正值;四季的地表辐射强迫分别为-564, -225, -137, -187W/m2;辐射强迫数值对矿物尘气溶胶单次散射反照率的变化较敏感.  相似文献   

15.
The modifications of some atmospheric physical properties prior to a high magnitude earthquake were debated in the frame of the Lithosphere Atmosphere Ionosphere Coupling (LAIC) model. In this work, among the variety of involved phenomena, the ionisation of air at the ionospheric levels triggered by the leaking of gases from the Earth’s crust was investigated through the analysis of GNSS (Global Navigation Satellite System) signals. In particular, the authors analysed a 5 year (2008–2012) long series of GNSS based ionospheric TEC to produce maps over an area surrounding the epicentre of the L’Aquila (Italy, Mw = 6.3) earthquake of April 6th, 2009. The series was used to detect and quantify amplitude and duration of episodes of ionospheric disturbances by a statistical approach and to discriminate local and global effects on the ionosphere comparing these series with TEC values provided by the analysis of GNSS data from international permanent trackers distributed over a wider region. The study found that during this time interval only three statistically meaningful episodes of ionospheric disturbances were observed. One of them, occurring during the night of 16th of March 2009, anticipated the main shock by 3 weeks and could be connected with the strong earthquake of 6th of April. The other two significant episodes were detected within periods that were not close to the main seismic events and are more likely due to various and global reasons.  相似文献   

16.
Here we used Empirical Mode Decomposition(EMD) method to study seasonal variability and nonlinear trend of corrected AERONET Aerosol Optical Depth(AOD/Hi) and corrected PM10 mass concentrations(PM10×f(RH)) in Hong Kong during 2005–2011. AOD/Hi is highly correlated with PM10×f(RH) in semi-annual and annual time scales(with correlation coefficient 0.67 for semi-annual and 0.79 for annual components, 95% confidence interval). On the semi-annual scale, both AOD/Hi and PM10×f(RH) can capture the two maxima in March and October, respectively, with much stronger amplitude in March probably due to the long-range transport of dust storm. On the annual cycle, the AOD/Hi and PM10×f(RH), which are negatively correlated with the precipitation and solar radiation, vary coherently with the maxima in February. This annual peak occurs about one month earlier than the first peak of the semi-annual variability in March, but with only half amplitude. During 2005–2011, both AOD/Hi and PM10×f(RH) exhibit the pronounced decreasing trend with the mean rate of 14 μg m–3 per year for PM10×f(RH), which reflects the significant effects of the air pollution control policy in Hong Kong during the past decade. The nonlinear trend analysis indicates that the decreasing of PM10×f(RH) is slower than that of AOD/Hi when the AOD/Hi is less than 0.44 but becomes faster when the AOD/Hi exceeds 0.44. These results illustrate that the AERONET AOD can be used quantitatively to estimate local air-quality variability on the semi-annual, annual, and long-term trend time scales.  相似文献   

17.
The main objective of this study is to develop algorithms for calculating the air surface temperature (AST). This study also aims to analyze and investigate the effects of greenhouse gases (GHGs) on the AST value in Peninsular Malaysia. Multiple linear regression is used to achieve the objectives of the study. Peninsular Malaysia has been selected as the research area because it is among the regions of tropical Southeast Asia with the greatest humidity, pockets of heavy pollution, rapid economic growth, and industrialization. The predicted AST was highly correlated (R = 0.783) with GHGs for the 6-year data (2003–2008). Comparisons of five stations in 2009 showed close agreement between the predicted AST and the observed AST from AIRS, especially in the wet season (within 1.3 K). The in situ data ranged from 1 to 2 K. Validation results showed that AST (R = 0.776–0.878) has values nearly the same as the observed AST from AIRS. We found that O3 during the wet season was indicated by a strongly positive beta coefficient (0.264–0.992) with AST. The CO2 yields a reasonable relationship with temperature with low to moderate beta coefficient (?0.065 to 0.238). The O3, CO2, and environmental variables experienced different seasonal fluctuations that depend on weather conditions and topography. The concentration of gases and pollution were the highest over industrial zones and overcrowded cities, and the dry season was more polluted compared with the wet season. These results indicate the advantage of using the satellite AIRS data and a correlation analysis to investigate the effect of atmospheric GHGs on AST over Peninsular Malaysia. An algorithm that is capable of retrieving Peninsular Malaysian AST in all weather conditions with total uncertainties ranging from 1 to 2 K was developed.  相似文献   

18.
Using vertical and oblique radio-sounding data, we analyze the ionospheric and thermospheric disturbances during the magnetic storm that occurred in northeastern Russia on March 17–19, 2015. We consider the heliospheric sources that induced the magnetic storm. During the main and early recovery phases, the midlatitude stations are characterized by extremely low values of electron density at the F2 layer maximum. Using oblique sounding data, we recorded signals that propagated outside the great circle arc. In evening and night hours, no radio signals were found to pass along the Norilsk–Irkutsk and Magadan–Irkutsk paths. The observed ionospheric effects are shown to be caused by a sharp shift of the boundaries of the main ionospheric trough to the invariant latitude 46° N during the main phase of the magnetic storm. The negative ionospheric disturbance during the recovery phase of the storm, which was associated with significant variations in the composition of the neutral atmosphere, led to a change in the mode composition of received radio signals and a decline in observed maximal frequencies in daytime hours of March 18, 2015 by more than 2 times.  相似文献   

19.
Chemical Composition of Sea Fog Water Along the South China Sea   总被引：4，自引：0，他引：4  
The chemical and microphysical properties of sea fog were measured during a field experiment on Donghai Island, Zhanjiang of China from March 15 to April 18, 2010. The average pH and electrical conductivity (EC) value of the six sea fog cases during the experiment was 5.2 and 1,884?μS/cm. The observed total ion concentration of sea fog was four orders of magnitude higher than those in the North Pacific and other sea areas of China. The dominant anion and cation in all sea fog water samples were Cl? and Na+, respectively. From backward trajectory analysis and ion loading computation, it can be concluded that the ions in the samples were transported either from pollutants in distant industrial cities or from local ion deposition processes. The concentration of Ca2+ in the sea fog water samples in Case 2 suggested that a dust storm in the Inner Mongolia, a northern region of China several thousand kilometers away, could reach the South China Sea. The data also showed that the sea fog droplet spectrum over the South China Sea is unimodal. Through relationship analysis, it is illustrated that the evolution of microphysics (such as droplet concentration, diameter, and liquid water content) during fog process could affect the chemical properties of sea fog.  相似文献   

20.
The results of studying the intensity of fluxes of 30–80 keV ions from the data of measurements of the NOAA (POES) sun-synchronous satellites during geomagnetic storms of different intensity are presented. For 15 geomagnetic storms with |Dst|max from ~37 to ~422 nT, the storm-time maximum ion fluxes in the near-equatorial region (trapped particles) and at high latitudes (precipitating particles) have been considered. It is shown that the maximum fluxes of trapped particles, which are considered a ring-current proxy, increase with the storm power. In this case, if a smooth growth of fluxes is recorded for storms with |Dst|max < 250 nT in the near-equatorial region, a significantly steeper growth of fluxes of trapped particles is observed when storm power increases during storms with |Dst|max > 250 nT. This may be evidence of both an increasing of the contribution of the ring current relative to magnetotail currents to the development of high-intensity storms and to a nonlinear link between the ring current and ion fluxes at low altitudes in the near-equatorial region. Despite large variations in fluxes of precipitating particles in the polar region above the boundary of isotropization, a decreasing tendency, as a whole, in fluxes of these particles is observed with increasing the storm intensity. This is the evidence of the effect of saturation of magnetotail currents and of an increase in the relative role of the ring current during strong magnetic storms.  相似文献   

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