The El Nino-Southern Oscillation and winter precipitation extremes over India

Daily rainfall data for the winter season October-December for the long period of 102 years 1901-2002 over southeast peninsular India have been used to study the characteristics of daily precipitation extremes. The frequency and intensity of extreme precipitation events do not show statistically significant long-term trend. The relationship of El Nino-southern oscillation index with these extremes shows that this index can be used to predict frequency and intensity of extreme precipitation events, 4-6 months in advance. However spell lengths of continuous wet/dry days are not modulated by variations in Pacific sea surface temperatures

Recent trends in pre-monsoon daily temperature extremes over India

Extreme climate and weather events are increasingly being recognized as key aspects of climate change. Pre-monsoon season (March-May) is the hottest part of the year over almost the entire South Asian region, in which hot weather extremes including heat waves are recurring natural hazards having serious societal impacts, particularly on human health. In the present paper, recent trends in extreme temperature events for the pre-monsoon season have been studied using daily data on maximum and minimum temperatures over a well-distributed network of 121 stations for the period 1970-2005. For this purpose, time series of extreme temperature events have been constructed for India as a whole and seven homogeneous regions, viz., Western Himalaya (WH), Northwest (NW), Northeast (NE), North Central (NC), East coast (EC), West coast (WC) and Interior Peninsula (IP). In general, the frequency of occurrence of hot days and hot nights showed widespread increasing trend, while that of cold days and cold nights has shown widespread decreasing trend. The frequency of the occurrence of hot days is found to have significantly increased over EC, WC and IP, while that of cold days showed significant decreasing trend over WH and WC. The three regions EC, WC and NW showed significant increasing trend in the frequency of hot nights. For India as whole, the frequency of hot days and nights showed increasing trend while cold days and nights showed decreasing trends. Day-to-day fluctuations of pre-monsoon daily maximum and minimum temperatures have also been studied for the above regions. The results show that there is no significant change in day-to-day magnitude of fluctuations of pre-monsoon maximum and minimum temperatures. However, the results generally indicate that the daily maximum and minimum temperatures are becoming less variable within the season

Anomalous behaviour of the Indian summer monsoon 2009

The Indian subcontinent witnessed a severe monsoon drought in the year 2009. India as a whole received 77 of its long period average during summer monsoon season (1 June to 30 September) of 2009, which is the third highest deficient all India monsoon season rainfall year during the period 1901-2009. Therefore, an attempt is made in this paper to study the characteristic features of summer monsoon rainfall of 2009 over the country and to investigate some of the possible causes behind the anomalous behaviour of the monsoon. Presence of El Niñno like conditions in the Pacific and warming over the equatorial Indian Ocean altered the circulation patterns and produced an anomalous low level convergence and ascending motion over the Indian Ocean region and large scale subsidence over the Indian landmass. Furthermore, the crossequatorial flow was weak, the monsoon was dominated by the slower 30-60 day mode, and the synoptic systems, which formed over the Bay of Bengal and the Arabian Sea, did not move inland. All the above features resulted in less moisture supply over the Indian landmass, resulting in subdued rainfall activity leading to a severe monsoon drought during 2009

Variations in atmospheric Carbon Dioxide and its association with rainfall and vegetation over India

In this paper we have studied variability and growth rate of surface observed atmospheric Carbon Dioxide (CO2) concentrations over Cape Rama, west coast of India and its association with rainfall and vegetation over this region. Cape Rama is a maritime site which experiences a seasonal reversal wind pattern receiving air masses having marine (continental) signatures during summer (winter) monsoon season. This study reveals that summer monsoon (JJAS) precipitation and monthly values of atmospheric CO2 concentration during the season are well correlated. Negative correlations are seen with CO2 concentrations of concurrent months of the season as well as subsequent months. However the magnitudes of correlation coefficients are decreased till hot pre-monsoon season (MAM). Annual cycle and interannual variability show negative relationship between CO2 concentration and vegetation over the region. CO2 concentration shows increasing trend and NDVI shows decreasing trend. However, the magnitude of increasing trend of CO2 concentration is higher. Amplitude of decreasing phase of vegetation is higher than the amplitude of increasing phase. Though the results show certain link between CO2 and climate variability, further examination with dense and longer data may be needed to confirm the result

Sensitivity of the Himalayan orography representation in simulation of winter precipitation using Regional Climate Model (RegCM) nested in a GCM

This document is the Accepted Manuscript version of the following article: Tiwari, P.R., Kar, S.C., Mohanty, U.C., Climate Dynamics (2017). The final publication is available at Springer via https://link.springer.com/article/10.1007%2Fs00382-017-3567-3. The Accepted Manuscript is under embargo. Embargo end date: 24 February 2018.The role of the Himalayan orography representationin a Regional Climate Model (RegCM4) nested inNCMRWF global spectral model is examined in simulatingthe winter circulation and associated precipitation over theNorthwest India (NWI; 23°–37.5°N and 69°–85°E) region.For this purpose, nine different set of orography representationsfor nine distinct precipitation years (three years eachfor wet, normal and dry) have been considered by increasing(decreasing) 5, 10, 15, and 20% from the mean height(CNTRL) of the Himalaya in RegCM4 model. Validationwith various observations revealed a good improvementin reproducing the precipitation intensity and distributionwith increased model height compared to the resultsobtained from CNTRL and reduced orography experiments.Further it has been found that, increase in heightby 10% (P10) increases seasonal precipitation about 20%,while decrease in height by 10% (M10) results around 28%reduction in seasonal precipitation as compared to CNTRLexperiment over NWI region. This improvement in precipitationsimulation comes due to better representation ofvertical pressure velocity and moisture transport as thesefactors play an important role in wintertime precipitationprocesses over NWI region. Furthermore, a comparison of model-simulated precipitation with observed precipitationat 17 station locations has been also carried out. Overall,the results suggest that when the orographic increment of10% (P10) is applied on RegCM4 model, it has better skillin simulating the precipitation over the NWI region andthis model is a useful tool for further regional downscalingstudies.Peer reviewe

Recent extremes in total ozone content over the northern parts of India in view of the Montreal Protocol

The Montreal Protocol on substances that deplete the ozone layer entered into force on 1 January 1989. One of the major questions is whether or not the atmosphere is on the path to ozone recovery due to the implementation of the Montreal Protocol and its amendments. In view of this, the frequency of the low/high ozone days and lowest /highest total ozone content (TOC) values have been analysed over the northern parts of India in the winter season for the time periods 1979-1988 and 1997-2005. Daily station total ozone data from TOMS on the Nimbus-7 (1979-1988) and Earth Probe (1997-2005) satellites of the National Aeronautics and Space Administration (NASA)/Goddard Space Flight Center (GSFC) during the period 1979-2005 are used in the present analysis. Stations located to the north of 20°N latitude regions of India have been chosen for the study. To compare the recent changes with extremes prior to the implementation of the Montreal Protocol, statistical percentile thresholds are computed based on the daily ozone data during winter months (January and February) for the period 1979-1988, and using these percentile threshold values extremes in TOC are computed for both time periods (1979-1988 and 1997-2005) to determine whether the day is a low, high or normal ozone day. Trends in extremes in TOC over northern India during the recent period (1997-2005) compared to the period prior to the implementation of the Montreal Protocol (1979-1988) in general indicate recovery of TOC either in terms of opposite trends or similar trends that are less in magnitude. However, most of the trends are statistically insignificant, probably due to the dynamic variability of the atmosphere

Association between ENSO and extremes in total ozone content over northern India

Using daily station total ozone column (TOC) data from the Total Ozone Mapping Spectrometer (TOMS) onboard the Nimbus-7 satellite, an association between the El Niño-Southern Oscillation (ENSO) and extremes in TOC content has been revealed during the period 1979-1993 over northern India in the winter season. From lag-simultaneous correlations of extremes in ozone with Niño 3.4 sea surface temperatures (SSTs), it is seen that, during this season, the highest TOC values show a strong positive relationship at the beginning of the preceding year with the occurrence of the highest values for all the stations. A weak relationship is observed up to the month of July and its sign is then reversed. The negative but weak relationship continues until the occurrence of the event, becoming positive again afterwards. On the contrary, the occurrence of the lowest values shows opposite features. The analysis indicates that the increase in SSTs during the first half of the preceding year is favourable for an increase in the highest values occurring over different stations while the increase in SSTs during the latter half of the preceding year is favourable for an increase in the lowest values of ozone. The lag-simultaneous correlations of the low/high ozone days and the mean TOC values occurring during the winter season also suggest a significant positive relationship for the frequency of the high ozone days at the beginning of the preceding year, becoming weaker as time progresses. Although both features show that the relationship is statistically significant for only a few months of the preceding year, it gives a broad indication of the association between ENSO and the extremes in the TOC amount in addition to local/geographical factors

On the surface air temperature variation in relation to chlorofluorocarbons over the Indian region

Chlorofluorocarbons (CFCs) are among the greenhouse gases in the atmosphere that contribute to warming. Therefore, an attempt is made in the present study to examine the variation in the surface temperature in relation to CFCs over the Indian region during 1992-2007. Space-time distribution of correlation coefficients (CCs) between CFCs and monthly temperature show positive CCs except pre-monsoon months. From April onwards up to onset of monsoon over the country, CCs are negative. It clearly indicates that higher (lower) temperature values are associated with the lower (higher) values of CFCs in these months. This may be because of convection occurred over the country playing some role in association with CFC. Interannual variation of CFCs has contrasting behavior in the two epochs (1) 1992-1997 and (2) 1999-2007 where the CFCs increase and decrease respectively. It is seen that during increasing phase of CFCs, trends in temperature are also increasing except pre-monsoon months which show negative CCs. Trend magnitudes over the northern latitudes are higher. Though decreasing phase of CFCs show similar features, trend magnitude of temperature have substantially decreased. Regional analysis with temperature homogeneous regions, show positive CCs between CFCs and minimum temperature during most of the months. Analysis with regional maximum temperature shows negative trends starting from the month of May up to the month of July. Though further studies may be needed, the results observed in the present analysis show that the variation in surface air temperature indeed has a certain link with the changes in CFCs over Indian region

Kharif foodgrain yield and daily summer monsoon precipitation over India

Foodgrain yield over India during kharif (summer) season is directly affected by day to day variations in summer monsoon precipitation (June through September). An increase (decrease) in foodgrain yield is generally associated with an increase (decrease) in rainfall. However, the reduction of rainfall or occurrence of heavy rainfall activity may cause adverse effect on the crop growth. This study is therefore aimed at understanding the impact of all possible values of daily precipitation from lowest to highest rainfall during summer monsoon on kharif foodgrain yield over India for the period 1966-2003. The study also includes an impact of intense rainfall events (1 and 5 days maximum precipitation) on foodgrain yield. Analysis covers frequency of rainy days based on all fixed thresholds (1 mm and above) at the interval of 1 mm as well as percentile thresholds (1st percentile to 99th percentile) at the interval of 1 percentile. The study reveals that the kharif foodgrain yield increases with increase in all-India summer monsoon precipitation and rainy days. Strong positive relationship (statistically significant at 1 level) is observed for lower range of threshold values from 1 to 50 mm (1st percentile to 90th percentile), and the magnitudes of correlation decreases with increase in threshold values. The negative impact of the heavy rainfall activity is more pronounced over the heavy rainfall regions of northeast India. It is found that the prolonged occurrence of intense rainfall activity increases their impact on the foodgrain yield. Normal (moderate) range of precipitation indices is seen to be associated with both positive and negative anomalies of foodgrain yield, which point towards the influence of other climatic factors in determining the better yield of kharif foodgrain