moisture flux
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Atmosphere ◽  
2022 ◽  
Vol 13 (1) ◽  
pp. 81
Author(s):  
Zahra Ghassabi ◽  
Ebrahim Fattahi ◽  
Maral Habibi

Analyzing atmospheric circulation patterns characterize prevailing weather in a region. The method of principal component analysis and clustering was used to classify daily atmospheric circulation patterns. The average daily geopotential height of 500 hPa with 0.5° resolution of the ECMWF (1990–2019) were extracted from the Middle East. The S array was used to identify air types, and k-means clustering was used to classify daily air types. All days were divided into eighteen groups. Then, the surface maps and moisture flux divergence at the 850-hPa level of each pattern were studied. The, the connection between circulation patterns and precipitation occurrence is investigated by the PI index. The existence of a variety of precipitation and temperature regimes and consequent dry/wet periods is related to the type and frequency of the circulation patterns. In patterns with south to southwesterly currents, the low-pressure surface center extends from the south of the Red Sea to southern Turkey and is associated with the mid-level trough, where the moisture fluxes converge in the south of the Red Sea, southwest/south of Iran, and east of the Mediterranean Sea. Therefore, according to the intensity of the patterns, the most precipitation falls in the country’s western half, and the Zagros Mountain’s wind side. With the eastward movement of the Cyclonic patterns, the rainfall area extends to the eastern half of the country. With the pattern that the thermal low surface pressure extends to 35 °N latitude and is associated with the mid-level subtropical high, almost no rain occurs in the country.


2022 ◽  
Author(s):  
Abayomi A. Abatan ◽  
Simon F. B. Tett ◽  
Buwen Dong ◽  
Christopher Cunningham ◽  
Conrado M. Rudorff ◽  
...  

AbstractThe State of São Paulo, Brazil (SSP) was impacted by severe water shortages during the intense austral summer drought of 2013/2014 and 2014/2015 (1415SD). This study seeks to understand the features and physical processes associated with these summer droughts in the context of other droughts over the region during 1961–2010. Thus, this study examines the spatio-temporal characteristics of anomalously low precipitation over SSP and the associated large-scale dynamics at seasonal timescales, using an observation-based dataset from the Climatic Research Unit (CRU) and model simulation outputs from the Met Office Hadley Centre Global Environment Model (HadGEM3-GA6 at N216 resolution). The study analyzes Historical and Natural simulations from the model to examine the role of human-induced climate forcing on droughts over SSP. Composites of large-scale fields associated with droughts are derived from ERA-20C and ERA-Interim reanalysis and the model simulations. HadGEM3-GA6 simulations capture the observed interannual variability of normalized precipitation anomalies over SSP, but with biases. Drought events over SSP are related to subsidence over the region. This is associated with reduced atmospheric moisture over the region as indicated by the analysis of the vertically integrated moisture flux convergence, which is dominated by reduced moisture flux convergence. The Historical simulations simulate the subsidence associated with droughts, but there are magnitude and location biases. The similarities between the circulation features of the severe 1415SD and other drought events over the region show that understanding of the dynamics of the past drought events over SSP could guide assessment of changes in risk of future droughts and improvements of model performance. The study highlights the merits and limitations of the HadGEM3-GA6 simulations. The model possesses the skills in simulating the large-scale atmospheric circulations modulating precipitation variability, leading to drought conditions over SSP.


MAUSAM ◽  
2021 ◽  
Vol 43 (1) ◽  
pp. 71-76
Author(s):  
K. PRASAD

A numerical analysis of the synoptic situation leading to devastating floods in Punjab and adjoining states during September 1988 has been carried out. The analysis is done by three dimensional multivariate optimum interpolation (OI) scheme cast on 1° x 1° Lat./Long. Grid. Software has been developed for computation of several derived parameters and linked with the basic flow variable analysis. A diagnostic study of day-to-day rainfall versus the objectively analysed grid point fields of integrated horizontal flux divergence of water vapour is carried out, The study brings out a close spatial correspondence between the area of net moisture flux convergence on the analysis day and the area of heavy rainfall on the following day. The study suggests that the numerical analysis products can be of a good predictive value to a synoptic forecaster In heavy rainfall predictions under difficult and uncertain synoptic situations.


2021 ◽  
Vol 13 (24) ◽  
pp. 5179
Author(s):  
Chiao-Wei Chang ◽  
Wei-Ting Chen ◽  
Yi-Chun Chen

We constructed the A-Train co-located aerosol and marine warm cloud data from 2006 to 2010 winter and spring over East Asia and investigated the sensitivities of single-layer warm cloud properties to aerosols under different precipitation statuses and environmental regimes. The near-surface stability (NSS), modulated by cold air on top of a warm surface, and the estimated inversion strength (EIS) controlled by the subsidence are critical environmental parameters affecting the marine warm cloud structure over East Asia and, thus, the aerosols–cloud interactions. Based on our analysis, precipitating clouds revealed higher cloud susceptibility to aerosols as compared to non-precipitating clouds. The cloud liquid water path (LWP) increased with aerosols for precipitating clouds, yet decreased with aerosols for non-precipitating clouds, consistent with previous studies. For precipitating clouds, the cloud LWP and albedo increased more under higher NSS as unstable air promotes more moisture flux from the ocean. Under stronger EIS, the cloud albedo response to aerosols was lower than that under weaker EIS, indicating that stronger subsidence weakens the cloud susceptibility due to more entrainment drying. Our study suggests that the critical environmental factors governing the aerosol–cloud interactions may vary for different oceanic regions, depending on the thermodynamic conditions.


2021 ◽  
Vol 4 (3) ◽  
pp. 1-9
Author(s):  
N. A. Shaporina ◽  
E. A. Sayb

The aim of the study. To assess the possibilities of using the Decagon EC-5 sensor in research practice, especially under the conditions of its stationary installation; and to study with its help the dynamics of soil profile moistening and moisture migration under different weather conditions. Location and time of the study. The study was carried out on the territory of the Ust-Kamensky (forest-steppe) research station of the Institute of Soil Science and Agrochemistry of the Siberian Branch of the Russian Academy of Sciences (55.005507 N, 83.858635 E). The object of the study was the dark gray forest soil (Luvic Greyzemic Phaeozem). Five Decagon EC-5 sensors were installed at 9, 13, 18, 22 and 27cm depths in a small (30cm deep) soil pit and connected to the Em50 recorder. The necessary calibration was carried out beforehand. The sensors functioned from June 13 to July 7, 2017. Main results. The study showed that this device is suitable for a wide range of applications. According to the sensor readings, it was possible to trace the migration of moisture within the soil profile, as well as to differentiate it into gravitational and capillary water, as well as to establish the fact of precipitation with an accuracy of an hour and to calculate the precipitated amount. Statistical analysis of the obtained data showed low values of data variance and the coefficient of variation, which indicated high data homogeneity. The use of these sensors can improve the traditional flood method for determining the maximum soil water holding capacity. Moreover, detailed recording of soil moisture, provided by Decagon EC-5 sensors, in combination with Thermochron sensors for soil temperature recording, allows to study quantitative indicators of thermal gradient moisture flux at a new level. Conclusions. The study showed that Decagon EC-5 sensors comply with their technical specification and have good prospects for usage both in research and agricultural production. Provided its preliminary calibration and producing the calibration curves for the studied soils, the sensors allow quick and accurate measurement of the soil volumetric moisture content. The frequency and rate of sensor readings takes research on the dynamics and migration of moisture in soils to an entirely new level.


MAUSAM ◽  
2021 ◽  
Vol 47 (3) ◽  
pp. 259-268
Author(s):  
Y.E. A. RAJ

The thermodynamic structure of the atmosphere over coastal Tamilnadu during the northeast monsoon season has been studied in detail based on the daily 0000 UTC upper air data between 1000  and 500 hPa levels of Madras for October-January for the l0 year period 1976-77 to 1985-86. Normal upper  air soundings have been computed for dry and wet spells of northeast monsoon and for the brief period of southwest monsoon prior to northeast monsoon onset. The moisture flux crossing  Madras and the liquid  water content over Madras have been computed for various categories of monsoon activity. It has been shown that the onset of easterlies over Madras is accompanied by a cooling of 1C of the atmosphere over Madras at all levels upto 500 hPa. An east to west moisture flux of 21.1 x 108 metric tons per day across one degree wall over Madras has been found to cross coast during typical wet spell of northeast monsoon. The moisture flux crossing coast for good northeast monsoon and also the normal flux computed for the period of study compared fairly well with the moisture flux crossing west coast during southwest monsoon obtained in various other studies. The energy of an air column over coastal Tamilnadu was found to decrease subsequent to the onset of northeast monsoon. Analysis of variation of liquid water content revealed that even during deficit rainfall years there was considereable amount of low level moisture in  the atmosphere. Neither during dryspells of northeast monsoon nor after its retreat was there any clear sign of spreading of continental air mass over coastal Tamilnadu.  


Abstract We investigated the relationship between the frequency of occurrence of the Orinoco Low-Level Jet (OLLJ) and hydroclimatic variables over northern South America. We use data from the ERA5 atmospheric reanalysis to characterize the spatial and temporal variability of the OLLJ in light of the LLJ-classification criteria available in the literature. An index for the frequency of occurrence of an LLJ was used, based on the hourly maxima of wind speed. The linkages among the OLLJ, water vapor flux, and precipitation were analyzed using a composite analysis. Our results show that during December–January–February (DJF), the OLLJ exhibits its maximum wind speed, with values around 8–10 m/s. During DJF, the analysis shows how the OLLJ transports atmospheric moisture from the Tropical North Atlantic Ocean. During this season, the predominant pathway of the OLLJ is associated with an area of moisture flux divergence located over northeastern South America. During JJA, an area of moisture flux convergence associated with the northernmost location of the ITCZ inhibits the entrance of moisture from northerlies. We also show that the occurrence of the OLLJ is associated with the so-called cross-equatorial flow. During DJF, the period of strongest activity of the OLLJ is associated with the northerly cross-equatorial flow and dry season, whereas during JJA the southerly cross-equatorial flow from the Amazon river basin predominates and contributes to the rainy season over the Orinoco region.


2021 ◽  
pp. 1-60

Abstract The present study investigated impacts of strong and weak El Niño events on Central Asian precipitation variability from El Niño developing years to decaying years. It is found that strong El Niño events persistently enhance Central Asian precipitation from the mature winter to decaying summer. Large warm sea surface temperature (SST) anomalies in the tropical central-eastern Pacific induce anomalous upper-level divergence and updraft over Central Asia through large-scale convergence and divergence in the mature winter and decaying spring. Meanwhile, the associated wind anomalies induce anomalous eastward and northeastward moisture flux from the North Atlantic and Arabian Sea to Central Asia. Both anomalous ascent and moisture flux convergence favor above-normal precipitation over Central Asia in the mature winter and decaying spring. The El Niño events induced Central Asian precipitation anomalies are extended to the decaying summer due to the role of soil moisture. Increased rainfall in winter and spring enhances soil moisture in the following summer, which in turn, contributes to more precipitation in summer through modulating regional evaporation. During weak El Niño events, significant wet anomalies are only seen in the developing autumn, which result from anomalous southeastward moisture flux from the Arctic Ocean, and the abnormal signals are weak in the other seasons. The different responses of Central Asian precipitation to strong and weak El Niño events may be attributed to the difference in intensity of tropical SST anomalies between the two types of events.


2021 ◽  
Author(s):  
Stefan Brönnimann ◽  
Peter Stucki ◽  
Jörg Franke ◽  
Veronika Valler ◽  
Yuri Brugnara ◽  
...  

Abstract. European flood frequency and intensity change on a multidecadal scale. Floods were more frequent in the 19th (Central Europe) and early 20th century (Western Europe) than during the mid-20th century and again more frequent since the 1970s. The causes of this variability are not well understood and the relation to climate change is unclear. Palaeoclimate studies from the northern Alps suggest that past flood-rich periods coincided with cold periods. In contrast, some studies suggest that more floods might occur in a future, warming world. Here we reconcile the apparent contradiction by addressing and quantifying the contribution of atmospheric processes to multidecadal flood variability. For this, we use long series of annual peak streamflow, daily weather data, reanalyses, and reconstructions. We show that both changes in atmospheric circulation and moisture content affected multidecadal changes of annual peak streamflow in Central and Western Europe over the past two centuries. We find that during the 19th and early 20th century, atmospheric circulation changes led to high peak values of moisture flux convergence. The circulation was more conducive to strong and long-lasting precipitation events than in the mid-20th century. These changes are also partly reflected in the seasonal mean circulation and reproduced in atmospheric model simulations, pointing to a possible role of oceanic variability. For the period after 1980, increasing moisture content in a warming atmosphere led to extremely high moisture flux convergence. Thus, the main atmospheric driver of flood variability changed from atmospheric circulation variability to water vapour increase.


2021 ◽  
Author(s):  
Sherly Shelton

Abstract Atmospheric moisture transportation associated with the occurrence of relatively wet and dry southwest monsoon (SWM) years over Sri Lanka is still not fully understood. This study focused on investigating the role of moisture transport in contrast SWM years. We selected seven wet (SWMWet) and nine dry (SWMDry) years for 1985-2015 and found that the whole country experiences above-average (below average) rainfall in SWMWet (SWMDry) years. In SWMWet years, strengthening moisture-laden low-level jets (LLJ) from the Arabian Sea bring a large amount of moisture towards Sri Lanka. In contrast, the weakening of the LLJ from the Arabian Sea direction is observed in SWMDry years. As a consequence, the climatological mean of net moisture flux (4.35 ×105 kg s-1) over the study domain is increased (5.33×105 kg s-1) and decreased (3.98 ×105 kg s-1) in SWMWet and SWMDry years, respectively. With respect to long-term Vertically Integrate Moisture Flux Divergence (VIMFD, –3.28×10-5 kg m-2 s-1), negative anomalous VIMFD (–1.78×10-5 kg m-2 s-1) in SWMWet years and positive anomalous VIMFD (1.44×10-5 kg m-2 s-1) in SWMDry years are recorded, which ascribed above-average and below-average rainfall over the country. Furthermore, strong moisture convergence (divergence) center in the western/ southwestern part of Sri Lanka during the SWMWet (SWMDry) years explain why strong positive and negative SWM rainfall anomalies are concentrated in these two regions. Furthermore, results highlighted a strong relationship between net moisture flux availability and SWM rainfall (r= 0.63) that may explain the observed SWM rainfall variability over the country.


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