Winter Monsoon Season Research Articles

Seasonal variations of physico-chemical factors and diversity of desmids (Algae) in Shahpura lake of Bhopal, India

The study aimed at determining the seasonal variations of physico-chemical aspects and their effects on diversity of desmids in Shahpura Lake of Bhopal, India. The physico-chemical parameters of the Lake, like, water temperature, transparency, pH, DO, total hardness, calcium hardness, chloride, phosphate, and nitrate were studied and data analyzed. The Desmidaceae taxa of winter, summer, monsoon and post monsoon seasons from December 2006 to November 2007 have been identified, resulting 36 species in 5 genera, and their monthly variations are presented.

From accelerated warming to warming hiatus in China

ABSTRACTAs the recent global warming hiatus has attracted worldwide attention, we examined the robustness of the warming hiatus in China and the related dynamical mechanisms in this study. Based on the results confirmed by the multiple data and trend analysis methods, we found that the annual mean temperature in China had a cooling trend during the recent global warming hiatus period, which suggested a robust warming hiatus in China. The warming hiatus in China was dominated by the cooling trend in the cold season, which was mainly induced by the more frequent and enhanced extreme‐cold events. By examining the variability of the temperature over different time scales, we found the recent warming hiatus was mainly associated with a downward change of decadal variability, which counteracted the background warming trend. Decadal variability was also much greater in the cold season than in the warm season, and also contributed the most to the previous accelerated warming. We found that the previous accelerated warming and the recent warming hiatus, and the decadal variability of temperature in China were connected to changes in atmospheric circulation. There were opposite circulation changes during these two periods. The westerly winds from the low to the high troposphere over the north of China all enhanced during the previous accelerated warming period, while it weakened during the recent hiatus. The enhanced westerly winds suppressed the invasion of cold air from the Arctic and vice versa. Less frequent atmospheric blocking during the accelerated warming period and more frequent blocking during the recent warming hiatus confirmed this hypothesis. Furthermore, variation in the Siberian High and East Asian winter monsoon season supports the given conclusions.

Thermodynamic and dynamic structure of atmosphere over the east coast of Peninsular Malaysia during the passage of a cold surge

An intense field observation was carried out for a better understanding of cold surge features over Peninsular Malaysia during the winter monsoon season. The study utilizes vertical profiles of temperature, humidity and wind at high vertical and temporal resolution over Kota Bharu, situated in the east coast of Peninsular Malaysia. LCL were elevated during the passage of the cold surge as the relative humidity values decreased during the passage of cold surge. Level of Free Convection were below 800hPa and equilibrium levels were close to the LFC in most of the cases. Convective available potential energy and convection inhibition energy values were small during most of the observations. Absence of local heating and instability mechanism are responsible for the peculiar thermodynamic structure during the passage of the cold surge. The wind in the lower atmosphere became northeasterly and was strong during the entire cold surge period. A slight increase in temperature near the surface and a drop in temperature just above the surface were marked by the passage of the cold surge. A remarkable increase in specific humidity was observed between 970 and 900hPa during the cold surge period. Further, synoptic scale features were analyzed to identify the mechanism responsible for heavy rainfall. Low level convergence, upper level divergence and cyclonic vorticity prevailed over the region during the heavy rainfall event. Dynamic structure of the atmosphere as part of the organized convection associated with the winter monsoon was responsible for the vertical lifting and subsequent rainfall.

Feeding ecology and consumption rates of yellowfin tuna (Thunnus albacares) in the eastern Arabian Sea

Diet composition, predator-prey relationships and consumption rates of yellowfin tuna Thunnus albacares in the western Indian Exclusive Economic Zone (eastern Arabian Sea) were studied by stomach content analysis. Stomachs of 406 specimens in the fork length range of 48 to 165.5 cm caught during exploratory longlining conducted in the eastern Arabian Sea during 2006 to 2009 were examined, of which, 15.52% were empty. Purple back flying squid ( Sthenoteuthis oualaniensis ) was the dominant prey species, followed by the swimming crab ( Charybdis smithii ), bigeye cigarfish ( Cubiceps pauciradiatus ) and flyingfishes (family Exocoetidae). Diet breadth index and the modified Costello diagram showed dominance of few prey species which are available in high densities in the Arabian Sea, indicating opportunistic feeding nature of this apex predator. Diet did not significantly differ between sexes and size groups. Higher food intake during premonsoon and winter monsoon indicated a seasonal variation in diet. A steady increase in the abundance of C. smithii and a decrease in the proportion of S. oualaniensis in the diet were observed from premonsoon to winter monsoon seasons. Yellowfin tuna in the Arabian Sea consume an average of 545.65 g of food in a day and require daily ration of 1.95% body weight per day.

Vertical profiles of optical and microphysical particle properties above the northern Indian Ocean during CARDEX 2012

Abstract. A detailed analysis of optical and microphysical properties of aerosol particles during the dry winter monsoon season above the northern Indian Ocean is presented. The Cloud Aerosol Radiative Forcing Experiment (CARDEX), conducted from 16 February to 30 March 2012 at the Maldives Climate Observatory on Hanimaadhoo island (MCOH) in the Republic of the Maldives, used autonomous unmanned aerial vehicles (AUAV) to perform vertical in situ measurements of particle number concentration, particle number size distribution as well as particle absorption coefficients. These measurements were used together with surface- based Mini Micro Pulse Lidar (MiniMPL) observations and aerosol in situ and off-line measurements to investigate the vertical distribution of aerosol particles.Air masses were mainly advected over the Indian subcontinent and the Arabian Peninsula. The mean surface aerosol number concentration was 1717 ± 604 cm−3 and the highest values were found in air masses from the Bay of Bengal and Indo-Gangetic Plain (2247 ± 370 cm−3). Investigations of the free tropospheric air showed that elevated aerosol layers with up to 3 times higher aerosol number concentrations than at the surface occurred mainly during periods with air masses originating from the Bay of Bengal and the Indo-Gangetic Plain. This feature is different compared to what was observed during the Indian Ocean Experiment (INDOEX) conducted in winter 1999, where aerosol number concentrations generally decreased with height. In contrast, lower particle absorption at the surface (σabs(520 nm) = 8.5 ± 4.2 Wm−1) was found during CARDEX compared to INDOEX 1999.Layers with source region specific single-scattering albedo (SSA) values were derived by combining vertical in situ particle absorption coefficients and scattering coefficients calculated with Mie theory. These SSA layers were utilized to calculate vertical particle absorption profiles from MiniMPL profiles. SSA surface values for 550 nm for dry conditions were found to be 0.94 ± 0.02 and 0.91 ± 0.02 for air masses from the Arabian Sea (and Middle East countries) and India (and Bay of Bengal), respectively. Lidar-derived particle absorption coefficient profiles showed both a similar magnitude and structure as the in situ profiles measured with the AUAV. However, primarily due to insufficient accuracy in the SSA estimates, the lidar-derived absorption coefficient profiles have large uncertainties and are generally weakly correlated to vertically in situ measured particle absorption coefficients.Furthermore, the mass absorption efficiency (MAE) for the northern Indian Ocean during the dry monsoon season was calculated to determine equivalent black carbon (EBC) concentrations from particle absorption coefficient measurements. A mean MAE of 11.6 and 6.9 m2 g−1 for 520 and 880 nm, respectively, was found, likely representing internally mixed BC containing particles. Lower MAE values for 880 and 520 nm were found for air masses originating from dust regions such as the Arabian Peninsula and western Asia (MAE(880 nm) = 5.6 m2 g−1, MAE(520 nm) = 9.5 m2 g−1) or from closer source regions as southern India (MAE(880 nm) = 4.3 m2 g−1, MAE(520 nm) = 7.3 m2 g−1).

Temporal Variation of Physico-chemical Parameters and Ostracoda Population, off Rameswaram, Gulf of Mannar, Southeast Coast of Tamil Nadu, India

Abstract Seasonal observation on physico-chemical parameters were correlated with population of ostracoda in southern region off Rameswaram, Gulf of Mannar, Ramanathapuram district, Tamil Nadu, southeast coast of India, by collecting bottom sediment and water samples in the inner shelf region. 11 samples were collected every season, for four different seasons, namely, northeast monsoon (October 2010), winter (January 2011), summer (April 2011) and southwest monsoon (July 2011) seasons. Spatial and seasonal variation in physico-chemical and hydrographic parameters and sampling stations having higher population of ostracoda were critically analysed with the observed parameters. Highest population of ostracoda was recorded during summer followed by southwest monsoon, northeast monsoon and winter season. Cluster analysis reveal that station 9 falls in all seasons under favourable location, during different seasons and is having the most congenial environment for ostracoda to thrive. Depth, pH, dissolved oxygen, salinity, EC, TDS, nitrite and silica show positive correlation, and turbidity, nitrate and phosphate show negative correlation with total population of ostracoda.

Climate change trends in some of the rubber growing regions of North-East India

<div><table cellspacing="0" cellpadding="0" align="center"><tbody><tr><td align="left" valign="top"><p>Climate change analysis has been conducted using daily surface meteorological datasets in respect of nine parameters from five rubber growing locations in the East and North-East India. Monthly, seasonal and annual variability in meteorological parameters showed decreasing trends in relative humidity, sunshine hours and pan evaporation rates coupled with increasing temperature extremes. Rise in mean temperature was seen to be highest (0.34 0C per decade) for Dhenkanal which experiences dry sub-humid type of climate. The data on relative humidity and temperature also revealed the fact that warm surface temperatures, along with limited moisture availability, may lead to lower relative humidity in the future, since all the stations are away from the moist coastal belts. Decreasing trends in sunshine hours were mainly observed during winter and post monsoon seasons with decreasing number of days even with the optimum required daily sunshine hours. The fact that there were no significant changes in the amount of rainfall or the number of rainy days was in conformity with several earlier reports in the northeast. Mean monthly decadal variations have also been tested with earlier and recent sets. With long term trends in most of the weather parameters, being lesser when compared to that of the traditional rubber growing regions in India, it is imperative that for rubber cultivation to thrive in this non-traditional belt, future policy inputs will have to be based depending on the magnitude of climate change effects.</p></td></tr></tbody></table></div>

Aerosol optical properties over a coastal site in Goa, along the west coast of India

Spectral characteristics of the Aerosol optical depths (AODs) measured over a coastal site in Goa (15.46°N and 73.83°E), from a plateau ~50m above mean sea level, for the period 2008–2010, are analyzed to understand the inter-seasonal and intra-seasonal variability and to delineate different aerosol sources. A Microtops-II sunphotometer having five different wavelengths centered at 0.380, 0.440, 0.500, 0.675 and 0.870µm was used to estimate AODs in different seasons classified as: winter monsoon season from December to March (WMS), spring inter-monsoon season from April to May (SIMS), summer monsoon season from June to September (SMS) and fall inter-monsoon season from October to November (FIMS). The number of data (AODs) generated in each season is 569 in WMS, 131 in SIMS, 38 in SMS and 256 in FIMS. The highest AOD at 500nm (AOD500) was recorded in SIMS (0.43±0.18) while the lowest value was observed in SMS (0.32±0.10). The seasonal mean values of Ångström α computed from the least-square method in the wavelength range 0.440–0.870μm showed higher values (1.23±0.20) in FIMS than those in SMS (0.75±0.34). The highest Ångström β values were noticed in SIMS (0.25±0.10) and lowest in FIMS (0.17±0.06). To make a source appropriation and thus to resolve the complexity of aerosols in the study area, α was computed in different wavelength ranges, viz: short wavelengths (0.440–0.500μm) and long wavelengths (0.675–0.870μm), which revealed differing α values for different ranges of wavelengths. To account for the curvature, a second order polynomial fit is introduced. Subsequently, the second-order Ångström exponent (ά) and the coefficient of the second-order polynomial fit are analyzed to understand the dominant aerosol type.

Observed interannual variability of near‐surface salinity in the Bay of Bengal

AbstractAn in situ gridded data of salinity, comprising Argo and CTD profiles, has been used to study the interannual variability of near‐surface salinity (within 30 m from sea surface) in the Bay of Bengal (BoB) during the years 2005–2013. In addition to the broad agreement with earlier studies on the north‐to‐south gradient of surface salinity and general features of seasonal variability of salinity, the data also revealed few episodes of enhanced freshening in the BoB. The observations showed distinct anomalous low salinity (< 2 psu) waters in the northern BoB during June–February of the years 2006–2007 (Y67), 2011–2012 (Y12), and 2012–2013 (Y23). The anomalous freshening during these years showed similar life cycle, such as, it starts in the northern BoB during July–September of current summer and extends up to February–March of next winter with a southward propagation. Analysis showed that the oceanic and atmospheric conditions associated with positive Indian Ocean Dipole (pIOD) lead to these freshening events, and IOD rather than El Niño/Southern Oscillation (ENSO) controls the interannual variability of salinity in the BoB. The mixed layer salt budget analysis indicated the dominant role of local fresh water flux (horizontal advection) on the observed salinity tendency during summer (winter) monsoon season. Enhanced precipitation associated with pIOD lead to enhanced freshening in northern BoB during June–September, which remained to this region with prevailing summer monsoon circulation. The weakening or absence of southward east India coastal current (EICC) during October–December of these freshening years trapped anomalous freshwater in the northern BoB.

Study of Impact of Climatic Variability on the Sea Surface Temperature and Chlorophyll-a Concentration Using Statistical Analysis on Satellite Derived Data for the Arabian Sea

The impact of long term variation in sea surface temperature (SST) on marine biomass using long-term satellite remote sensing data (1985 - 2006) for SST and (1998 – 2010) for chlorophyll-a was studies. This paper presents the result of the analysis conducted on t wenty one year’s data on high-quality satellite derived Sea Surface Temperature, and twelve years SeaWiFS chlorophyll-a data from Arabian Sea. The results are extracted after processing the data using statistical methods for computation of inter-annual seasonal mean and standard deviation. The mean winter data show that region consisting on Gulf of Oman is colder (< 21 o C) than the rest of Arabian Sea. However, annual mean of winter show the intermittent rise and fall in SST in response to El-Nino occurred in 1986, 1988, 1991–1995, 1997-1998, 2002, 2006 and La-Nino events which occurred in 1985, 1986, 1989, 1996, 1999 and 2000 years. The results of SST means for summer and Post-Summer seasons differ from the phenomenon observed in winter and Pre-Summer. During summer, SST of major part of the western Arabian Sea lower to 15 o C under the influence of up-welled water off Somalia and Oman coast. The results of chlorophyll-a concentration depict the increase of concentration with the lowering of SST in the area of northern Arabian Sea. Similar results are obtained for standard deviation computations of both parameters of sea surface during winter monsoon season. Whereas, the results of Standard Deviation for summer monsoon show the minimum values (<1) in the northern and central Arabian Sea and maximum in the alignment of zone under Ekman process. The comparison with temperature confirms the dependency of productivity of the sea surface.

Identification of major factors affecting spatial and temporal variation of water quality in Kathmandu Basin, Nepal, using multivariate statistical analysis

Statistical techniques were applied to analyse the water quality datasets of Kathmandu Basin, Nepal, to identify the major factors affecting water quality and to investigate the spatial and seasonal variations. Spatial variation was investigated using cluster analysis in which a total of 40 river monitoring sites were divided into two major clusters: low and high polluted zones. Discriminant analysis (DA), principal component analysis (PCA) and factor analysis (FA) were subjected to water quality parameters to identify the pollution sources. DA confirmed the seasonal variation of water quality data into three seasons providing 92.5% correct classification. Principal components (PCs) were extracted to distinguish the anthropogenic processes and the symmetrical correlation matrix computed with ten variables for winter, monsoon and post monsoon seasons. The significant components extracted have eigenvalues greater than 1, and account for 79%, 68% and 77% of the total variance in the winter, monsoon and post monsoon data respectively. Non-parametric tests were applied for each parameter to identify their significance differences spatially and temporally.

Nutritional evaluation of fodder, its preference and crop raiding by wild Asian elephant (Elephas maximus) in Sonitpur District of Assam, India

Aim: The present investigation was carried out to evaluate the nutritive value of fodder in natural habitat, cultivated crops and their preference by wild Asian elephant (Elephas maximus) in forest and non-forest areas in four seasons using field observation in Sonitpur District of Assam; since, there were frequent incidences of crop raiding by wild elephant leading to loss of property and human-elephant conflict. Materials and Methods: The study was conducted in four seasons. The study included forest areas of Sonai-Rupai Wildlife Sanctuary, part of Nameri National Park and high human-elephant conflicted areas of non-forest near to the sanctuary and parks. The consumed fodders were identified, collected and evaluated. The proximate composition was determined using AOAC (1990). Results: Total 39 different fodder species of 18 families including herbs, climber, grasses, paddy seeds, paddy saplings, plants and its leaves, bark, fruits, and roots were recorded to be utilized by elephants. The first three family of fodder that elephant relished more were Poaceae (46.15%), Musaceae (7.69%) and Zingiberaceae (5.13%) respectively. The crude protein content of fodder in all seasons, total ash content only in winter and post monsoon seasons and neutral detergent fiber content of fodder between forest and non-forest were significant (p<0.05). Elephants preferred to forage more on nutritionally rich fodder than poor natural fodder. Incidence of crop raiding was more in post monsoon season could be due to availability of nutritionally rich fodder than the poor natural fodder and generally happened in the night. Conclusions: The study revealed that during post monsoon season, there were abundant nutritionally rich sources of cultivated crops than the fodder of natural habitat that might provoke the wild elephants to raid crops. Poaceae shared a major portion of their diet. The findings will definitely help nutritionist, ecologist and policy makers to understand wild elephant’s needs and also to take appropriate measures for conservation of endangered wild Asian elephant as well as mitigation of human-elephant conflict.

Impact of outdoor meteorology on indoor PM10, PM2.5 and PM1 concentrations in a naturally ventilated classroom

This paper discusses the effect of meteorological parameters (temperature, relative humidity, solar radiation, pressure, wind speed, wind direction and precipitation) on indoor coarse (PM10) and fine (PM2.5 and PM1) particles in a naturally ventilated classroom. The indoor PM10, PM2.5 and PM1 mass concentrations and meteorological parameters were monitored for 222 days during winter, summer, monsoon and post monsoon seasons of 2011 and 2012. The occurrence of atmospheric stagnation, recirculation and ventilation events at the study site was also estimated. It was found that the occurrence of stagnation was comparatively more frequent in post monsoons (74–81%) and winters (53–76%), recirculation in monsoon season (46%) and ventilation in summer seasons (45–59%). Maximum PM concentrations were also observed under stagnant atmospheric conditions. The highest concentrations of coarse and fine particles in the classroom were associated with strong and low winds respectively. Among the other meteorological variables, temperature (R2=0.32–0.47), relative humidity (R2=0.34–0.36) and precipitation (R2=0.13–0.27) showed moderate dependence with indoor PM concentrations. However, solar radiation (R2=0.06–0.15) and atmospheric pressure (R2=0.16–0.21) showed poor correlation with indoor PM concentrations.

TYPHOONS DRIVEN MORPHODYNAMICS OF THE WAN-TZU-LIAO SAND BARRIER (TAÏWAN)

This study focuses on the dynamics of the Wan-Tzu-Liao sand barrier when it is struck by one typhoon, a group of typhoons or the whole season of typhoons and monsoon. In the framework of the KUN-SHEN project, 7 months of monitoring (2011-2012) provided 20 topobathymetric surveys (within a 200 m long segment of the barrier from the subtidal zone to the back-barrier) and acquisitions of offshore, nearshore and shallow water hydrodynamics including velocity profiling, free surface measurement and absolute pressure. Offshore waves were extracted at Cigu buoy (18 m of water depth). Nearshore waves were acquired from the current profiler deployed 400 m off the coast in 4 m of water depth and water level on the subaerial beach were acquired from two pressure sensors deployed in the lower part of the subtidal zone and the dune crest. Morphologic changes of the emerged beach were monitored using D-GPS each week during winter monsoon season and just before and after each event during summer typhoons season. Amongst the eight studied typhoons, TALIM is the most energetic event observed. Offshore wave height reached H s = 10.34 m (T p = 14.6 s) at Cigu buoy and H s = 2.3 m (T p = 13.4 s) at the profiler. Surface waves dynamics throughout surf and swash zones are progressively dominated by infragravity motions. A part of the dune is surged at the storm apex. Morphological changes include 6.7 m of dunefoot retreat and a sand transfer from a dune breach to wash-over deposits in the lagoon. More surprisingly, the foreshore was nourished (2261 m3 +/- 268 m3 ) as well as the whole sand barrier (+1920 m3 +/- 1071 m3 ). The sand input is concomitant to the redistribution of sand from the intertidal sandbars interpreted as the ultimate stage of the subtidal bars landward migration. Although winter are erosive season (-4995 m3 +/- 1071 m3 ), the summer results in an accretion period (3556 m3 +/-1071 m3 ) with a shoreline seaward shift about 10.4 m. Over the annual time period, the sand barrier recorded 18.4 m of retreat coupled with a small sand loss (-1439 m3 +/- 1071 m3 ) without any significant abrasion of the dune-top.

REALISTIC SIMULATION OF INSTANTANEOUS NEARSHORE WATER LEVELS DURING TYPHOONS

3D hydrodynamic simulations were performed on an area extending 600 km off Taiwan island for the period running from September 2011 to December 2012. We covered a winter Monsoon season and a summer season with 17 typhoons recorded. By comparing simulations and measurements during the TALIM typhoon, our model reproduces correctly the storm surge observed along the Wan-Tzu-Liao sand barrier (South-West Taiwan). By a modelling approach, we analyzed the regional hydrodynamic mechanisms which control the sea surface elevation at the Chung-Chin harbour. Tide is the dominant forcing of the water level with more than 1 meter above the mean sea level. Global currents contribute up to 80 cm to the water level but during the SAOLA typhon, the elevation reached 1 meter. The contribution of atmospheric forcings is lower but it can generate 30 cm of elevation (e.g. during GUCHOL and TALIM typhoons)

Variation in the orographic extreme rain events over the Meghalaya Hills in northeast India in the two halves of the twentieth century

The daily rainfall data for the twentieth century, from three stations across the region, constitute the basis for statistical analysis. However, the low signal-to-noise ratio makes it difficult to find any significant departure from the simplest null hypothesis of the stability of the rain record at individual stations in northeast India. Only the coarsest possible view, i.e. comparing the two halves of the century, provided strongly significant results in the numbers of days with extreme rain. Using a more general approach, the number of Fourier transform extreme amplitudes also differed significantly. Increasingly heavy events during the summer monsoon season, and partly in the pre- and post-monsoon seasons, are offset by a weakening in the winter monsoon season, so that the annual mean rainfall does not show a significant trend over the Meghalaya Hills. Apart from a greater number of years with noticeable extreme rainfall events in the second half of the twentieth century, we can also observe a more pronounced quasi-periodicity of 10–20 and 30–60 days during the same period. The detection of the latter periodicity indicates that the Madden–Julian oscillation plays an important role in the formation of extreme rainfall events over the Meghalaya Hills during extreme monsoon years.

Climate projections for Vietnam based on regional climate models

This study uses an ensemble of regional climate models (RCMs) to simulate and pro- ject the climate of Vietnam. Outputs of 3 global climate models are dynamically downscaled using 3 RCMs. Experiments are performed for a baseline period from 1980 to 1999 and for a future pro- jection from 2000 to 2050 with the A1B emission scenario. Verifications against observations at 61 selected meteorological stations in the region show that an ensemble mean of the 3 RCMs outper- forms the individual RCM in representing the climatological mean state, and reasonably captures some extreme climate indices such as the annual maximum daily temperature (TXx), the annual minimum daily temperature (TNn), and the annual maximum 1 d precipitation (RX1day). Future ensemble projections of the temperature, precipitation, and 3 different extreme indices are then evaluated. The simulations predict the 2 m air temperature over Vietnam to significantly increase in both the near future 2011�2030 and middle-future 2031�2050 periods compared to the baseline period. The temperature trend tends to be positive and significant over the whole Vietnam for the spring, summer and fall periods, whereas it is insignificant in the north central region during win- ter. The highest increase of ~0.5°C decade �1 appears to be pronounced in summer. For precipita- tion, future changes vary depending on regions and seasons, with the most significant increasing trend over the coastal plain of Central Vietnam, particularly during the winter monsoon season. Under the global warming scenario A1B, TXx and TNn show a significant increase, with the high- est rate in the northern and central highlands regions of Vietnam. The extreme precipitation RX1day indices show increasing trends for the coastal zone in the south central region of Vietnam, suggesting more severe water-related disasters in this region in the future.

Trends in seasonal temperatures over the Indian region

An investigation has been carried out to identify the trends in maximum, minimum and mean temperatures and temperature range over the Indian land mass during the winter (January, and February), pre-monsoon (March–May), southwest monsoon (June–September) and post-monsoon (October–December) seasons by using high resolution daily gridded data set prepared by India Meteorological Department for the period of 1969–2005. It has been observed that the maximum temperatures over the west coast of India show rising trend in winter, southwest monsoon and post-monsoon seasons but the maximum temperatures do not show any significant trend over the other parts of the country. Minimum temperatures show increasing trend over the North Indian states in all seasons and they show an increasing trend over the west coast of India in winter and southwest monsoon seasons. Mean temperature shows an increasing trend over the west coast of India during winter and southwest monsoon seasons. Decreasing trend is observed in the temperature range over North India in all seasons due to increasing trend in minimum temperature.

Soil heat flux and day time surface energy balance closure at astronomical observatory, Thiruvananthapuram, south Kerala

Soil heat flux is an important input component of surface energy balance. Estimates of soil heat flux were made in the year 2008 using soil temperature data at Astronomical Observatory, Thiruvananthapuram, south Kerala. Hourly values of soil heat flux from 00 to 24 LST are presented for selected days typical of the winter, pre-monsoon, SW monsoon and NE monsoon seasons. The diurnal variation is characterized by a cross-over from negative to positive values at 0700 h, occurrence of maximum around noon and return to negative values in the late evening. The energy storage term for the soil layer 0–0.05 m is calculated and the ground heat flux G ∗ is estimated in all seasons. Daytime surface energy balance at the surface on wet and dry seasons is investigated. The average Bowen’s ratio during the wet and dry seasons were 0.541 and 0.515, respectively indicating that considerable evaporation takes place at the surface. The separate energy balance components were examined and the mean surface energy balance closure was found to be 0.742 and 0.795 for wet and dry seasons, respectively. When a new method that accounts for both soil thermal conduction and soil thermal convection was adopted to calculate the surface heat flux, the energy balance closure was found to be improved. Thus on the land surface under study, the soil vertical water movement is significant.

Simulation of stable water isotopic composition in the atmosphere using an isotopic Atmospheric Water Balance Model

ABSTRACTIn this article, we present a simplified isotopic Atmospheric Water Balance Model (iAWBM), to simulate spatial distribution and temporal variations of δ18O in atmospheric vapour and in precipitation, and the correlations of δ18O in precipitation with precipitation amount and with temperature. This method overcomes deficiencies of the Global Network of Isotopes in Precipitation (GNIP) due to its limitation in space and time resolution and those of the isotope‐enabled General Circulation Models (iGCMs) due to its complexity. The simulated results reproduce well the latitude effect, continent effect and seasonality of δ18O in global precipitation. The simulation suggests that the precipitation amount effect occurs mainly in the low‐mid latitude oceans and monsoon areas, and the simulated temperature effect occurs mainly in the mid‐high latitude continents. However, the simulation results also indicate some temperature effect in some low‐latitude areas where the precipitation amount effect is strong. The modelled precipitation isotopic composition is compared to 3‐year observations in Changsha, China (2010–2012). The simulations reproduce the observed seasonal variations of δ18O in precipitation. The basic characteristics that stable isotopes in precipitation are depleted during the rainy season and enriched during the dry season, and the observed amount effect is well simulated under daily time scale. The simulated weighted average δ18O (−6.58‰) in precipitation during the prevailing winter monsoon season (October–March) is almost the same as the observed δ18O in the same period (−6.56‰), but the simulated δ18O (−9.58‰) during the prevailing summer monsoon season (April–September) is lower than the observed δ18O (−7.66‰). The simulation result also shows temporal variations of vapour isotopic composition in the atmosphere, and the proportional contributions from horizontal vapour exchange, precipitation and evaporation.