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The study has focused on the evaluation of model performance on simulated air temperature at surface and mid atmospheric level over the Indian subcontinent using a Regional Climate Model version 3 (RegCM3). The model is used at 40 km horizontal resolution over the domain approximately 58° E-102.5° E & 5° N-40° N for the period of 1982-2006. The temperatures at lower troposphere (850 hPa) and mid tropospheric level (500 hPa) have been simulated with reanalysis dataset of the National Centre for Environmental Prediction (NCEP). Various statistical measures namely Mean Bias Error (MBE), Root Mean Square Error (RMSE), Mean Percentage Error (MPE) and Correlation Coefficients (CCs) has been used to test the model results. It has been found that the RegCM3 is able to capture the main features of the observed mean surface climate and also patterns of surface and mid-level air temperatures over India. The model showed that cold biases were -4.29 °C (16.4%) at the lower troposphere, but insignificant at the mid atmospheric level in comparison to the NCEP dataset. The air temperature was well captured at mid tropospheric level. The CC between RegCM3 and NCEP is significantly high (0.82) over India in respect of annual surface air temperature (SAT). The trends of observed SAT were found to be significant increased by 0.32 °C with NCEP and 0.40 °C with RegCM3 over India. The annual SAT of cold biases ranging between -2 °C to -5 °C was found over major parts of India while cold biases of above -5 °C was found in the regions of low elevation or valley regions and below -2 °C in the mountainous regions. The analysis of annual and seasonal trends of maximum air temperature (Tmax), minimum air temperature (Tmin) and average air temperature (Tave) showed that the increasing trend was found over the Indo-Gangetic plain, Western Himalayas (WH) and North East India (NEI) in all seasons while decreasing trend over the North Central India (NCI) in the summer season and over the state of Gujarat in the monsoon season. The RegCM3 showed higher Water Vapour Mixing Ratio (WVMR) at the lower troposphere resulting more cooling at surface rather than at mid tropospheric level.

This study has been attempted to investigate the seasonal and annual trends and variations in the occurrence of extreme rainfall over different Indian region and India as a whole. Trends and variations are examined on the basis of following parameters (i) frequency and magnitude of extreme rainfall intensity (ERI) and its contribution in total rainfall (ii) highest rainfall events (iii) frequency of extreme rainfall events and days (iv) frequency of rainfall events and days with daily rainfall above 100 mm and 200 mm in a grid box (1° × 1°) over different Indian regions and India as a whole. Daily gridded rainfall data from India Meteorological Department (IMD) available at 1° × 1° resolution has been used to examine trends and variations associated with extreme rainfall events. Based on the long term 95 and 99 percentile values of daily total /maximum rainfall as a threshold for extreme rainfall intensity/events of category 1 and category 2 respectively, the trends and variations in above mentioned parameters are analyzed for the periods 1951-2007, 1951-1980 and 1981-2007. The magnitude of highest intensity rainfall is increased over country as a whole and over peninsular India; it is found to be increased by 1% during 1981-2007 as compared to period 1951-1980. The frequency of extreme rainfall intensity (ERI) days of category 1 is found to be significant increasing (0.4 days/decade) over north central region and significant decreasing trend is found over north east region (0.5 days/decade) during the pre-monsoon season. The magnitude of 24 hours highest rainfall in a grid box is found to be significant increasing over all regions under consideration except over north east and south peninsular regions. Over the last ten years period of the present study, most of the 24 hours highest rainfall events in a grid box are seen over west peninsular region. Generalized extreme value (GEV) distribution fitted with annual highest rainfall event over the country as a whole and over different Indian region indicates an increase in magnitude of most probable 24 hours highest rainfall in a grid box during second half of the study period over north central region of the country. Analysis also reveals an increase in frequency and severity of extreme rainfall over north west, north central and west peninsular regions during the period of 1981-2007 as compared to 1950-1980. Annual frequency of days and events with extreme rainfall of both categories is increased most significantly over country during the period of present study (1951-2007). Significant increasing trends in frequency of days with extreme rainfall of both categories is noticed only during the monsoon season while extreme rainfall events showed increasing trends during monsoon and winter season over country as a whole. Number of days and events with daily rainfall in any grid box above 100 mm and 200 mm is observed to be significantly increased over the country. Out of six regions, significant increasing trends in annual number of days with rainfall above 100 mm in a grid box is observed over north central and north east regions and for rainfall above 200 mm significant increase is observed over north west and north central regions.

A study on pest population of American boll worm (Heliothis armigera H.) in cotton crop as influenced by weather parameters like rainfall (RF), maximum temperature (Tmax), minimum temperature (Tmin), morning relative humidity (RH I), evening relative humidity (RH II) and bright sunshine hours (BSS) and its statistical correlation was undertaken with data recorded at Dr. Punjabrao Deshmukh Krishi Vidhyapeeth, Akola. The maximum activity and damage due to high population of Heliothis was observed during 35th to 50th standard weeks. Maximum temperature (40th week) and minimum temperature (37th week), morning and evening relative humidity during 38th week play an important role in pest infestation during 40th standard week. Flowering to boll formation stages of the crop suffered heavy incidence of Heliothis. Critical weather parameters causing the outbreak of Heliothis in Akola was maximum temperature around 32 °C and minimum temperature around 23 °C, morning relative humidity below 88%, evening relative humidity below 60% and hours of bright sunshine above 6.5 hrs / day.

The Historical Soviet Daily Snow Depth (HSDSD) version II data set has been used to examine the empirical relationship between the winter/spring snow depth anomaly over three different regions of Eurasia and Indian Summer Monsoon Rainfall (ISMR). HSDSD data show that the difference in snow depth between two extreme years is most prominent over western Eurasia in the month of April and the inverse relationship between the spring snow depth anomaly and the following ISMR is very robust with correlation coefficient of –0.43 at 5% significant level. Examination of seasonal mean circulation pattern using NCEP/NCAR reanalysed data shows that low level atmospheric temperature difference between two extreme years of high and low western Eurasia snow depth in April can be as large as 10°C which gives rise to anomalous cyclonic circulation over the Caspian Sea and this may be responsible for affecting the monsoon circulation over India. Results also show that there is a complete phase reversal in the dipole structure of the upper tropospheric velocity potential anomaly from the deficient to excess ISMR irrespective of occurrence of different phases of ENSO events or high/low Eurasian snow. However, during opposite phases of ENSO, the divergence center has east-west shift as compared to the high Eurasian snow when the divergence center shifts to the southeast over Australia.

The monthly mean atmospheric fields and surface parameters of NCEP/NCAR reanalysis for the period 1948-1998 have been studied to examine the characteristics of monsoon circulation features, sea surface temperature (SST), sea level pressure, surface wind stress and latent heat flux over the Indian Ocean and nearby seas during deficient, normal and excess rain years. The entire period of study has been classified into deficient, normal and excess rain years for all India as well as for each of the five homogeneous zones separately based on the observed seasonal mean rainfall. On the basis of the mean characteristics of the surface fields, the oceanic region covering the Indian Ocean and adjacent seas has been divided into four regional sectors. Using various statistical means the relation between the surface fields over the four regional sectors and the monsoon rainfall over five homogeneous zones of Indian landmass has been examined. Attempt have been made to identify some surface parameters which can be used as predictors for seasonal mean monsoon rainfall over the entire India and also over some homogeneous zones.

The main objective of the present work is to investigate the influence of eastern Sea surface temperature (SST) anomalies during the Positive Tropical Indian Ocean dipole (PTIOD) events on regional summer monsoon rainfall especially over Tamilnadu and Coastal Andhra Pradesh (A. P.) for the period of 1980-2009. There were 7 strong PTIOD events recorded during the period of study which are accompanied by significant increase in the seasonal summer monsoon rainfall over India. Averaged SST anomalies (SSTA) over the EQ.ESIO (Equatorial Eastern South Indian Ocean) during AMJ (April, May, June) shows that colder (warmer) EQ.ESIO during AMJ and positive TIOD events were associated with the decreasing (increasing) tendency of summer monsoon rainfall over Tamilnadu and coastal A.P. The statistical analysis shows the correlation coefficient of 0.59 and 0.79 between AMJSST anomalies and the rainfall over Tamilnadu and Coastal A. P. respectively. Wind anomalies during PTIOD years with negative AMJSSTA, transports the cold upwelled oceanic current off Sumatra-Java towards the South West Bay of Bengal (SWBOB) and caused anomalous SST cooling in the region. Thus, the low level southerly wind reaching over the SWBOB during AMJ enforced the colder oceanic surface temperature of the region during the month of maximum solar insolation and thereby weak thermal gradient was observed with the shifting of the convective activity towards the south-east/northern Bay of Bengal (BOB). Moreover, less moisture advection with less convective activity in SWBOB region during pre-monsoon season may be the caused of the below-normal rainfall over Tamilnadu and coastal A. P. sub-divisions during June, July, August and September (JJAS)

The relationship between Indian northeast monsoon rainfall over Tamil Nadu (TNR) and southeast India (SER) as well as two indices of southern oscillation (SOI), and sea surface temperature (SST) anomalies over different Nino regions of equatorial Pacific Ocean and seven tropical circulation indices (TCI), have been studied for different periods. The study indicates that northeast monsoon rainfall (TNR) shows significant inverse relationship with SOI (I-D) during previous MAM (March- April-May) season. significant direct relationship with SST anomalies over Nino-4 region during previous JJA (June-July- August) and significant direct relationship with TCI (C-N) during previous DJF, The SOI (I-D), MAM correlates I significantly and negatively with both the northeast monsoon rainfall series, the TNR rainfall series displaying the better correlation. The strongest correlation is observed during 1961-90. For SSTA, the strongest correlation is during 1964-85 and for TCI, the highest correlation is observed during 1958-82.