Monsoon Months Of July Research Articles

Trans-boundary spatio-temporal analysis of Sentinel 5P tropospheric nitrogen dioxide and total carbon monoxide columns over Punjab and Haryana Regions with COVID-19 lockdown impact.

This study conducts a spatio-temporal analysis of tropospheric nitrogen dioxide (NO2) and total carbon monoxide (CO) concentrations in the Punjab and Haryana regions of India and Pakistan, using datasets from the Sentinel 5-Precursor (S5P) satellite. These regions, marked by diverse economic growth factors including population expansion, power generation, transportation, and agricultural practices, face similar challenges in atmospheric pollution, particularly evident in major urban centers like Delhi and Lahore, identified as pollution hotspots. The study also spotlights pollution associated with power plants. In urban areas, tropospheric NO2 levels are predominantly elevated due to vehicular emissions, whereas residential activities mainly contribute to CO pollution. However, precisely attributing urban CO sources is complex due to its longer atmospheric residence time and intricate circulation patterns. Notably, the burning of rice crop residue in November significantly exacerbates winter pollution episodes and smog, showing a more pronounced correlation with total CO than with tropospheric NO2 levels. The temporal analysis indicates that the months from October to December witness peak pollution, contrasted with the relatively cleaner period during the monsoon months of July to September. The severe pollution in the OND quarter is attributed to factors such as variations in boundary layer height and depletion of OH radicals. Furthermore, the study highlights the positive impact of the COVID-19 lockdown on air quality, with a significant decrease in NO2 concentrations during April, 2020 (Delhi: 59%, Lahore: 58%). However, the reduction in total CO columns was less significant. The study also correlates lockdown stringency with tropospheric NO2 columns (R2: 0.37 for Delhi, 0.25 for Lahore, 0.22 for Rawalpindi/Islamabad), acknowledging the influence of various meteorological and atmospheric variables. The research highlights the significant impact of crop residue burning on winter pollution levels, particularly on total CO concentrations. The study also shows the notable effect of the COVID-19 lockdown on air quality, significantly reducing NO2 levels. Additionally, it explores the correlation between lockdown stringency and tropospheric NO2 columns, considering various meteorological factors.

Active and break spells of summer monsoon over Bangladesh

This study examines the intraseasonal variability of the southwest summer monsoon over Bangladesh using rainfall data from rain gauge stations of the Bangladesh Meteorological Department (BMD) collected over 30 years (1988–2017). In this paper, active and break spells are defined as periods during the peak monsoon months of July and August, in which the daily precipitation lasts for three or more days at 0.5 above and below the daily climatological cycle. The active and break phases of the monsoon over a period of 10 years (2008–2017) were also analyzed by The Weather Research and Forecasting (WRF) model simulation for analysing synoptic conditions. The model simulations for each year were done for the period of 1 May to 30 September with 1 May as the initial condition with a single domain of 30 km resolution and 19 vertical levels. The final operational global analysis data from the Global Forecasting System of National Centers for Environment Prediction (NCEP-FNL) with resolution 1° × 1° is used for model simulation. The model-simulated daily rainfall, Sea Level Pressure (SLP), wind pattern at 850 hPa, 200 hPa, and Outgoing Longwave Radiation (OLR) are compared with the observations from Tropical Rainfall Measuring Mission (TRMM), ERA5 (ERA5 is the European Centre for Medium-Range Weather Forecasts fifth-gen global atmospheric reanalysis data), and Kalpana-1. This study also finds that the increase in rainfall is concurrent with a southwesterly wind and the decrease of rainfall simultaneously occurs with a southeasterly wind. Active days were found to have lower OLR values and lower SLP than break days.

Status of Swamp Deer Rucervus duvaucelii duvaucelii (G. Cuvier, 1823) in grassland-wetland habitats in Dudhwa Tiger Reserve, India

Swamp Deer is an endemic species of the Indian subcontinent, mainly inhabiting tall grasslands in river floodplains. Populations of the northern subspecies (Rucervus duvaucelii duvaucelii), restricted to the Terai regions of northern India and western Nepal, have undergone dramatic declines over the past two─three decades. In this communication, we present results from systematic population counts conducted in Dudhwa Tiger Reserve between 2021─2022. These counts were conducted at 11 sites, each with two─three independent observers. The exercises covered summer, monsoon, post-monsoon, and winter seasons. We found the largest congregations of Swamp Deer in June during the summer and February in winter. In the monsoon months of July─September the Swamp Deer tend to use Sal woodlands along with farmlands adjoining the reserve edge. This is part of an ongoing research project on long-term monitoring and conservation of the threatened alluvial grasslands of the central Terai in Uttar Pradesh, India. Institutionalizing these monitoring practices for frontline forest staff is essential for understanding long-term population dynamics of the threatened Swamp Deer to develop conservation protocols for grasslands and their fauna.

Assessment of cloudbursts, extreme rainfall and vulnerable regions in the Upper Ganga basin, Uttarakhand, India

The Upper Ganga Basin (UGB) of Himalayas, located in the state of Uttarakhand, has experienced flash floods caused by extreme rainfall (EREs) and cloudbursts (CBEs). Low predictability of EREs, coupled with insufficient monitoring and inventory of CBEs are limiting factors in the study and identification of Himalayan hazard-prone areas. In this study, 57 EREs/CBEs are compiled and geo-tagged from media reports between 2010 and 2020. These events are authenticated using TRMM/GPM data. The spatial distribution, recurrence and vulnerable areas are analyzed. Cloudbursts occur during the monsoon months of July and August (JA), with approximately 66.6% of events occurring in the elevation band of 1000–2000 m above sea level (m a.s.l.). This elevation band is a potential hazard zone as it is the most populous region in the state. Assessment of rainfall distribution suggests that areas with lower monsoon rainfall have a higher number of EREs/CBEs. This low rainfall valley region also experiences high land surface temperature (LST) in the range of 18 °C–28 °C during JA which could further increase CBEs occurrence highlighting the topography controls. The study identified Joshimath, Bhilangana, Bhatwari, Ukhimath, Dasholi, Deoprayag, Jakholi, Tharali, and Narayanbagad as the most vulnerable blocks and Chamoli, Rudraprayag and Tehri Garhwal as the most vulnerable districts. The assessment showed that about 1 million people spread across 3000 villages in the state are in higher risk regions of EREs/CBEs.

Animal Bites Presenting to the Emergency Department

Context: Animal bites including insect, reptile, and mammalian bites are common presentations to the emergency department (ED). Although profile and outcome of individual bites are described in detail, the literature on comprehensive overall clinical spectrum and seasonal variation of all animal bites is scant. Aims: To describe the spectrum, seasonal variation, clinical features, and outcomes of all patients presenting as emergencies due to animal bites. Methods: All the patients who presented to the ED of a large tertiary care hospital in South India with bites from January 2017 to December 2018 were retrospectively included in the analysis. Results: During the 2-year study period, animal bites constituted 0.83% of all ED admissions with 1145 incidents included in our analysis. The various animal bites/stings were classified as follows: mammal bites (480: 41.9%), arthropod bites (275: 24%), reptile bites (290: 25.3%), and unknown bites (100: 8.6%). We found an increase in the incidence of bites during the monsoon months of July to September (average: 58 cases per month) in our geographical locality. More than half (46: 58%) of scorpion stings had features of envenomation while a quarter (19: 24%) had the signs of autonomic storm. Snake bites constituted a quarter (25.2%: 289/1145) of all animal bites with 66% (191/289) showing features of envenomation. Dog bites constituted the majority of mammalian bites with 73% (352/480), followed by rat bites (14%: 68/480), cat bites (7.5%: 37/480), human bites (2.5%: 12/480), and monkey bites (1.9%: 9/480). The World Health Organization rabies exposure Category 3 bites were seen in 48%, 12%, and 27% of dog, rat, and cat bites, respectively. Conclusion: Snake and dog bites comprised the majority of all animal bites. There was a clear seasonal pattern with increased prevalence of bites during the rainy season.

Multi-year characterization of aerosol black carbon concentrations over a semiarid tropical site Udaipur.

Continuous and multi-year (2008-2012) measurements of black carbon (BC) mass concentrations (MBC), carried out from the semiarid tropical site Udaipur (24.6° N, 74° E, 580ma.s.l.) near the western Indian desert, are analyzed for their region-specific features. MBC varied over a wide range during the period of study, with the hourly mean values occurring as low as 0.09 to as high as 49.1μgm-3, with the multi-year average ~ 4.5 ± 2.6μgm-3. Annual variations showed the highest concentrations during November and December (winter seasonal mean = 7.4 ± 3.3μgm-3) and the lowest in the monsoon months of July and August (monsoon seasonal mean = 2.5 ± 2.2μgm-3). MBC showed significant inverse relationship with the planetary boundary layer height (ρ ~ - 0.50) as well as ventilation coefficient (ρ ~ - 0.72). Alike aforesaid atmospheric dynamic parameters, T, WS, and RH also possessed statistically significant negative correlations with monthly MBC. Enhancement in annual as well as diurnal amplitude in MBC during deficient monsoon years relative to excessive monsoon years have given marked indication of BC sink mechanism due to precipitation. Roles of long-range regional air pollutant transport also have been identified. Identical and consistent seasonal variation in percentage contribution of MBC with PM2.5 (varying from 2.6 to 9.1%) and absorption Angstrom exponent (αabs, monthly mean values varying from 0.77 ± 0.04 to 1.16 ± 0.08) gives evidence of substantial amount of enhanced anthropogenic source activities of fossil fuel incomplete combustion in post-monsoon and winter period.

Seasonality of Taylor\u2019s law of fluctuation scaling in all-India daily rainfall

Here we show that the variance over time of all-India daily rainfall (AIR) can be related to the mean over time of AIR by a seasonally varying power law. Outside of the peak monsoon months of July and August, AIR variance increases in proportion to a positive power of mean daily rainfall. During July and August, monthly averages of AIR show little association with the corresponding variances. This power-law relationship of temporal variance to temporal mean is known in biological sciences as Taylor’s law (TL) and in physical sciences as fluctuation scaling. We explain the seasonal variation in TL qualitatively by independent and identically distributed random sampling. Accounting for day-to-day correlation in AIR is sufficient to match quantitatively the observed power-law behavior. Our findings provide a quantitative month-specific assessment of the variability of AIR that could prove useful for the design of crop insurance and social safety nets for the large fraction of the population of the Indian subcontinent that depends on rainfed agriculture.

The Asymmetric Influence of the South China Sea Biweekly SST on the Abnormal Indian Monsoon Rainfall of 2002

An examination of the contrasting behaviour of the Indian summer monsoon during peak monsoon months of July and August 2002 in relation to the South China Sea (SCS) SST variations on intra-seasonal time scale have been carried out in this study. Monsoon rainfall over India was a deficit during July whereas enhanced rainfall activity was evident during August. Interestingly, SST over the SCS also exhibited similar contrasting behaviour with less variation during July and strong biweekly intra-seasonal (BWI) oscillation with 10–20 day periodicity during August. During August, the BWI oscillation in the SCS SST could induce anomalous cyclonic circulation and enhancement in rainfall over the SCS, suggestive of a strong air–sea interaction process. Moreover, a strong relationship between the Indian monsoon and SCS SST is evident during August, at 3-day lead time of SST. The SCS SST variations could enhance westward propagation of moisture flux from the SCS to the Indian subcontinent and thereby influences the Indian monsoon. The SST variations and air–sea interaction processes over the SCS, also westward propagation of BWI moisture flux were weak during July. Our analysis suggests that SST variations over the SCS could modulate the monsoon circulation as well as the moisture flux from the SCS to the Indian subcontinent and thereby influence the Indian monsoon, particularly on biweekly time scale at least 3 days in advance. The study indicates a potential role of the SCS SST in foreshadowing the biweekly intra-seasonal oscillation during the Indian summer monsoon period.

Performance Investigation of a Solar Heat Driven Adsorption Chiller under Two Different Climatic Conditions

The demand for cooling, especially in the developing economies, is rising at a fast rate. Fast-depleting sources of fossil fuel and environmental concerns necessitate looking for alternative cooling solutions. Solar heat driven adsorption based cooling cycles are environmentally friendly due to their use of natural refrigerants and the thermal compression process. In this paper, a performance simulation study of a basic two-bed solar adsorption chiller has been performed through a transient model for two different climatic locations in India. Effect of operating temperatures and cycle time on the chiller performance has been studied. It is observed that the solar hot water temperature obtained in the composite climate of Delhi (28.65°N, 77.25°E) can run the basic adsorption cooling cycle efficiently throughout the year. Whereas, the monsoon months of July and August in the warm and humid climate of Durgapur (23.48°N, 87.32°E) are unable to supply the required driving heat.

Assessment of TRMM-based TMPA-3B42 and GSMaP precipitation products over India for the peak southwest monsoon season

Reliable information of rainfall and its variability at finer spatio-temporal scales over the Indian monsoon region is crucial for various applications in hydrology, meteorology, water resource management, and evaluation of high-resolution numerical model outputs. In this study, the Tropical Rainfall Measuring Mission (TRMM)-based high-resolution multisatellite rainfall products namely, TRMM Multisatellite Precipitation Analysis (TMPA)-3B42 and Global Satellite Mapping of Precipitation (GSMaP) are evaluated against recently released gauge-based India Meteorological Department (IMD) gridded data set. Both the research (delayed mode) and near real-time rainfall products of TMPA-3B42 (V7 and RT) and GSMaP (MVK and NRT) are evaluated over India at a daily scale for the peak southwest monsoon months of July–August. Two study periods (2000–2010 and 2009–2013) are used to accommodate the analyses based on data availability. Comparison of TMPA-3B42 (V7 and RT) and GSMaP-MVK with IMD gauge-based data for 2000–2010 shows that these data sets are able to represent large-scale monsoon rainfall spatial features, but are having region-specific biases. The interannual variability of monsoon rainfall averaged over India is also reasonably captured. However in terms of biases, TMPA-3B42RT overestimates rainfall by about 21% and GSMaP-MVK underestimates by about 22% at all-India scale. In terms of continuous skill metrics, TMPA-3B42V7 is closer to the IMD gauge-based observations possibly due to gauge adjustments. Categorical verification against gauge-based observations shows that the satellite-based data sets have difficulties in rainfall detection primarily over the northern Jammu & Kashmir regions, northeast India, and southern peninsular India. At subregional scale within India, satellite rainfall estimates show rather lower skill score in rainfall identification and larger uncertainty in rainfall estimation over the northeast India. Comparison of near real-time products of TMPA and GSMaP for July–August months of 2009–2013 shows that TMPA-3B42RT overestimates and GSMaP-NRT underestimates rainfall over most parts of India. Even though TMPA-3B42 (V7 and RT) and GSMaP-MVK rainfall data sets show similar diurnal variations over the Indian monsoon region, TMPA-3B42RT (GSMaP-MVK) shows larger (smaller) magnitude in diurnal cycle as compared to TMPA-3B42V7. Results from different skill metrics suggest that both research and near real-time versions of TMPA products can be used with relatively higher confidence as compared to GSMaP over the Indian region during peak monsoon period.

The changing characteristics of monsoon rainfall in India during 1971-2005 and links with large scale circulation

This study examines the changes in monsoon rainfall of India using a suite of extreme indices defined by the Expert Team on Climate Change Detection Monitoring and Indices (ETCCDMI) to make the Indian results comparable internationally, in addition to the use of some relevant indices particularly developed for the Indian climate. To this end, the recently developed high resolution daily gridded (0.5° × 0.5°) rainfall dataset for the period 1971–2005 has been analysed using robust nonparametric techniques. Despite the high interannual variability and spatial diversity of the Indian climatology, the results reveal signal of changes for several extreme rainfall indices, generally consistent with the simulated outcome of an intensified Indian monsoon rainfall in the context of global warming. A predominant decrease in wet days, moderate and total rainfall is observed in the high rainfall regions of northeast, central and southwest India. In the active monsoon months of July and August, the dry spells defined by the maximum length of consecutive dry days (CDD) have increased significantly over the north and central regions of India, suggesting a serious threat to the Indian agriculture. Simultaneously, the extreme rainfall indices, based on the percentile and absolute values, show increasing trends over large parts of the country. The probability density function (PDF) of several indices show noticeable changes since the 1990s over the homogeneous central and northeast parts of India. The indices representing the total monsoon rainfall and dry spells are better correlated with the El Nino–Southern Oscillation (NINO3.4), compared to that of the Indian Ocean Dipole Mode Index (IODMI). The mapping of the observed rainfall trends and their correspondence to the large scale circulation modes is expected to assist the policy makers to prioritize the mitigation and adaptation strategies.

Non-typhoidal Salmonella gastroenteritis at a diarrheal hospital in Dhaka, Bangladesh, 1996-2011.

Data on non-typhoidal Salmonella (NTS) infection in South Asia are limited. We used data gathered prospectively from 1996 to 2011 as part of a hospital surveillance system in Dhaka, Bangladesh, to identify diarrheal patients with NTS isolated from stool. NTS was isolated in 1.3% (468 of 37,439) of diarrheal patients; 47% of total cases of NTS were in children < 5 years of age, although older adults (≥ 60 years) had the highest isolation rates. NTS isolation peaked in the monsoon months of July and August. Over the study period, rates of multidrug resistance decreased, whereas rates of decreased susceptibility to ciprofloxacin increased. Compared with control patients, NTS patients were older and wealthier; however, no differences in type of housing or exposure to animals were found. NTS patients had increased inflammatory cells in stool and required more fluid resuscitation.

Some aspects of squall over Indira Gandhi International airport, New Delhi

A study is undertaken to analyse the characteristics of squall over Delhi and to find out the potential precursors for its prediction. For this purpose, the squall data of Indira Gandhi International (IGI) airport along with the surface and upper air meteorological parameters recorded by India Meteorological Department have been considered for all individual months over the period of 2001-2010. Apart from the characteristics like period of occurrence, intensity, duration, frequency and nature of squall, the environmental changes due to squall and thermodynamic features and indices leading to squall have been analysed.&#x0D; Higher than normal warming of lower troposphere upto 700 hPa level in March, April &amp; June and at 925 hPa in May accompanied with cold dry air advection leading to lower than normal dew point in middle and upper levels (500-300 hPa in March, May and June, 400-300 hPa in April) are favourable for occurrence of the squall over Delhi. The lower level inversion in March and April only also helps in the occurrence of squall. In monsoon months of July- September, cold and dry air advection in middle and upper tropospheric levels (8- 15° C below normal dew point at 400-300 hPa in July, about 15° C below normal dew point at 300-200 hPa in August and 17- 24° C below normal dew point at 500-300 hPa in September) favours occurrence of squall over Delhi. Unlike pre-monsoon months lower level moisture does not play any role for the occurrence of squall over Delhi in monsoon months. Significantly higher than normal SWEAT index in March to September at 0000 UTC can be used as predictor of squall over Delhi on that day. Total totals index is the next suitable precursor for all the months except June.

Moisture transport over the Arabian Sea associated with summer rainfall over Pakistan in 1994 and 2002

In this study, we aimed to elucidate the critical role of moisture transport affecting monsoon activity in two contrasting summers over the Arabian Sea during the years 1994, a relatively wet year, and 2002, a relatively dry year. A comprehensive diagnostic evaluation and comparisons of the moisture fields were conducted; we focused on the precipitation and evaporation as well as the moisture transport and its divergence or convergence in the atmosphere. Monthly mean reanalysis data were obtained from the National Centers for Environmental Prediction (NCEP-I and -II). A detailed evaluation of the moisture budgets over Pakistan during these two years was made by calculating the latent energy flux at the surface (E-P) from the divergence of the total moisture transport. Our results confirm the moisture supply over the Arabian Sea to be the major source of rainfall in Pakistan and neighboring regions. In 1994, Pakistan received more rainfall compared to 2002 during the summer monsoon. Moisture flow deepens and strengthens over Arabian Sea during the peak summer monsoon months of July and August. Our analysis shows that vertically integrated moisture transport flux have a significant role in supplying moisture to the convective centers over Pakistan and neighboring regions from the divergent regions of the Arabian Sea and the Bay of Bengal. Moreover, in 1994, a deeper vertically integrated moisture convergence progression occurred over Pakistan compared to that in 2002. Perhaps that deeper convergence resulted in a more intense moisture depression over Pakistan and also caused more rainfall in 1994 during the summer monsoon. Finally, from the water budget analysis, it has been surmised that the water budget was larger in 1994 than in 2002 during the summer monsoon.

Active and break spells of the Indian summer monsoon

In this paper, we suggest criteria for the identification of active and break events of the Indian summer monsoon on the basis of recently derived high resolution daily gridded rainfall dataset over India (1951–2007). Active and break events are defined as periods during the peak monsoon months of July and August, in which the normalized anomaly of the rainfall over a critical area, called the monsoon core zone exceeds 1 or is less than −1.0 respectively, provided the criterion is satisfied for at least three consecutive days. We elucidate the major features of these events. We consider very briefly the relationship of the intraseasonal fluctuations between these events and the interannual variation of the summer monsoon rainfall.We find that breaks tend to have a longer life-span than active spells. While, almost 80% of the active spells lasted 3–4 days, only 40% of the break spells were of such short duration. A small fraction (9%) of active spells and 32% of break spells lasted for a week or longer. While active events occurred almost every year, not a single break occurred in 26% of the years considered. On an average, there are 7 days of active and break events from July through August. There are no significant trends in either the days of active or break events. We have shown that there is a major difference between weak spells and long intense breaks. While weak spells are characterized by weak moist convective regimes, long intense break events have a heat trough type circulation which is similar to the circulation over the Indian subcontinent before the onset of the monsoon.The space-time evolution of the rainfall composite patterns suggests that the revival from breaks occurs primarily from northward propagations of the convective cloud zone. There are important differences between the spatial patterns of the active/break spells and those characteristic of interannual variation, particularly those associated with the link to ENSO. Hence, the interannual variation of the Indian monsoon cannot be considered as primarily arising from the interannual variation of intraseasonal variation. However, the signature over the eastern equatorial Indian Ocean on intraseasonal time scales is similar to that on the interannual time scales.

Seasonal Ensemble Predictions of West African Monsoon Precipitation in the ECMWF System 3 with a Focus on the AMMA Special Observing Period in 2006

Abstract The West Africa monsoon precipitation of the ECMWF operational Seasonal Forecast System (SYS3) is evaluated at a lead time of 2–4 months in a 49-yr hindcast dataset, with special attention paid to the African Monsoon Multidisciplinary Analysis (AMMA) special observation period during 2006. In both the climatology and the year 2006 the SYS3 reproduces the progression of the West Africa monsoon but with a number of differences, most notably a southerly shift of the precipitation in the main monsoon months of July and August and the lack of preonset rainfall suppression and sudden onset jump. The model skill at predicting summer monsoon rainfall anomalies has increased in recent years indicating improvements in the ocean analysis since the 1990s. Examination of other model fields shows a widespread warm sea surface temperature (SST) bias exceeding 1.5 K in the Gulf of Guinea throughout the monsoon months in addition to a cold bias in the North Atlantic, which would both tend to enhance rainfall over the Gulf of Guinea coast at the expense of the monsoon rainfall over the Sahel. Seasonal forecasts were repeated for 2006 using the same release of the atmospheric forecast model forced by observed SSTs, and the monsoon rainfall reverts to its observed position, indicating the importance of the SST biases. A lack of stratocumulus off the west coast of Africa in SYS3 was hypothesized as a possible cause of the systematic rain and SST biases. Two more sets of ensembles were thus conducted with atmospheric model upgrades designed to tackle radiation, deep convection, and turbulence deficiencies. While these enhancements improve the simulation of stratocumulus significantly, it is found that the improvement in the warm SST bias is limited in scope to the southern cold tongue region. In contrast, the changes to the representation of convection cause an increase in surface downwelling shortwave radiation that, combined with latent heat flux changes associated with the wind stress field, increases the SST warm bias on and to the north of the equator. Thus, while the precipitation shortfall in the Sahel is reduced with the new physics, the overestimated rainfall of SYS3 in the coastal region is further enhanced, degrading the model systematic errors overall in the West Africa region. Finally, the difference in the systematic biases between the coupled and uncoupled systems was noted to be an impediment to the development of seamless forecasting systems.

Verification of heavy rainfall warning over Bihar and Uttar Pradesh

India Meteorological Department (IMD) issues heavy rainfall warning for a meteorological sub-division when the expected 24 hours rainfall over any rain gauge station in that sub-division is likely to be 64.5 mm or more. Though these warnings have been provided since long and are also now being issued for smaller spatial scales, very few attempts have been made for quantitative evaluation of these warnings. Hence, a study is undertaken to verify the heavy rainfall warning over the representative meteorological sub-divisions of east Uttar Pradesh (UP), west UP and Bihar during main monsoon months of July and August. For this purpose data of the recent 5 years (2001-2005) and also for another epoch of 5 years in the early 1970s has been taken into consideration. In this connection, the day when heavy rainfall is recorded over atleast two stations in a sub-division, has been considered as a heavy rainfall day for that sub-division.&#x0D; &#x0D; This study of verification shows that probability of detection of heavy rainfall is 64% over Bihar, 52% over east UP and 53% over west UP for the recent 5 years. Compared to early 1970s, there has been slight improvement in the forecast skill during 2001-2005 with probability of detection increasing by about 10-20% and with decrease in missing rate and false alarm rate. However, the false alarm rates are still large indicating higher bias towards over-prediction. The synoptic conditions associated with the heavy rainfall events have been collected for the period 2001-05 and analysed. The analysis of the unanticipated heavy rainfall events suggests that though proper interpretation of synoptic charts and NWP outputs could improve the warnings, the forecast system available even today is still not capable to capture every heavy rain event in advance.

Identification of tropical convective tropopause and its association with cold point tropopause

Using the MST radar observations at Gadanki (13.5°N, 79.2°E), a tropical station, the altitude of major convective outflow in the troposphere is identified and is considered to represent the convective tropopause. This is found to match well with the altitude of local minimum of potential temperature lapse rate obtained from simultaneous radiosonde observations. The convective tropopause altitudes are also compared with the cloud top altitudes obtained using satellite brightness temperature (BT) data and are found to match in the case of deep convection. The thickness of the tropical tropopause layer follows very closely the convective tropopause altitude and has little dependence on the cold point tropopause altitude. The thickness of the tropopause layer is found to shrink when convection reaches high altitudes. This occurs mainly during the monsoon months of July, September, and October.

A new criterion for identifying breaks in monsoon conditions over the Indian subcontinent

The presence or absence of prolonged breaks over the Indian subcontinent during the mid monsoon months of July and August decides the fate of the monsoon rainfall. Using a new criterion for identifying the breaks, we have catalogued them for the period 1901 to 2002. We refer to a situation as a break, if the all India rainfall is less than 9 mm/day and the condition persists for a minimum of three days and if it occurs in the mid monsoon months of July and August. The majority of the breaks in the months of July and August were of 3–4 days duration (49%). Breaks identified by our method were in general consistent with those identified by the conventional methods. Further, the correlation between the seasonal monsoon rainfall and break (active) days identified by the present criteria is −0.80 (0.38) which is more robust than that of the previous studies.

Sea State Hindcast with ECMWF Data Using a Spectral Wave Model for Typical Monsoon Months

A third generation wave prediction model (WAM) suitably modified for the Indianseas was used to simulate the sea state during typical monsoon months of July 1987,88 and 89. During July 1987, small-scale disturbances over the Arabian Sea and theBay of Bengal as reported from earlier works were noticed in the wave hindcast. Thegridded monthly averaged wave heights for the above periods were compared with theGEOSAT altimeter data. A comparison between model computed wave parameters andavailable ship observations was also carried out for July 1987, 88 and 89.The modelwas run with ECMWF analyzed wind field for a period of one month. The comparisonshowed that the wave heights from the model matches with those from GEOSATAltimeter and ships of opportunity.