Showing papers in "Mausam in 2002"

Tropospheric temperature variation over India and links with the Indian summer monsoon : 1971-2000

Abstract: In the context of the ever increasing interest in the regional aspects of global warming, understanding the spatio-temporal variations of tropospheric temperature over India is of great importance. The present study, based on the data from 19 well distributed radiosonde stations for the period 1971-2000, examines the seasonal and annual mean temperature variations at the surface and five selected upper levels, viz., 850, 700, 500, 200 and 150 hPa. An attempt has also been made to bring out the association between tropospheric temperature variations over India and the summer monsoon variability, including the role of its major teleconnection parameter, the El Nino/Southern Oscillation (ENSO). Seasonal and annual mean all-India temperature series are analyzed for surface and five tropospheric levels. The mean annual cycles of temperature at different tropospheric levels indicate that the pre-monsoon season is slightly warmer than the monsoon season at the surface, 850 hPa and 150 hPa levels, while it is relatively cooler at all intermediate levels. The mean annual temperature shows a warming of 0.18° C and 0.3° C per 10 years at the surface and 850 hPa, respectively. Tropospheric temperature anomaly composites of excess (deficient) monsoon rainfall years show pronounced positive (negative) anomalies during the month of May, at all the levels. The pre-monsoon pressure of Darwin has significant positive correlation with the monsoon temperature at the surface and 850 hPa.

Predictive relationships between Indian Ocean sea surface temperatures and Indian summer monsoon rainfall

Abstract: Monthly sea surface temperature (SST) data of 49 years (1950-98) have been analysed to examine the relationship of SST anomalies in the Indian Ocean with Indian summer monsoon rainfall (ISMR) and to derive useful predictors for long-range forecasts of ISMR. There is significant positive relationship between ISMR and SST anomalies over the Arabian Sea during November to January and also in May. SST anomalies over southeast Indian Ocean during February to March and over North Pacific during May are also positively correlated with ISMR. The composite analysis revealed that in Non-ENSO drought years (1966, 1968, 1974 and 1979) negative SST anomalies are observed over south Indian Ocean from February which slowly spread towards equator during the subsequent months. These negative SST anomalies which persist during the monsoon season may be playing an important role in modulating ISMR especially in non-ENSO years. We have derived two indices, ARBSST (SST anomalies in Arabian Sea averaged over 15o - 25o N, 50o -70o E and November-December-January) and SIOSST (SST anomalies over south Indian Ocean averaged over 15o -30o S, 70o -110o E and February and March) as useful predictors for the long-range forecasts of ISMR. The correlation coefficient (for the period 1950-98) of ARBSST and SIOSST with ISMR is 0.45 and 0.46 respectively which is statistically significant at 99.9 % level. SIOSST index has shown consistently stable relationship with ISMR. However the ARBSST index showed significant correlation with ISMR only after 1976.

Relationship between surface fields over Indian ocean and monsoon rainfall over homogeneous zones of India

Abstract: 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.

Summer monsoon low pressure systems over the Indian region and their relationship with the sub-divisional rainfall

Abstract: In the present paper performance of the monthly sub-divisional summer monsoon rainfall is studied in association with the position of the Low Pressure System (LPS) over the Indian region. Existence of the LPS over a particular location increases the rainfall activities in certain parts of the country while decreases in some other parts. For this study, the Indian region (5°-35° N and 60° -100° E) is divided into 5° Lat. ´ 5° Long. grids. The duration of LPS is taken in terms of LPS days with respect to the location of LPS in a particular grid. Monthly total number of LPS days in each of the grids are computed during the summer monsoon season, June to September for the period 1891 – 1990. Maximum number of LPS days (more than half of the total) are observed in the latitude belt between 20°-25°N. The percentages of total LPS days in this area are higher in July and August which are peak monsoon months as compared to June and September. When there is a LPS are in the area 20°-25° N and 80°-90° E, there is significant increase in the rainfall activities in the sub-divisions along mean monsoon trough while northeast India and southeast peninsular India experience significant decrease in rainfall in the months of July and August. Owing to the movement of LPS from east to west through central India, most parts of the country, excluding northeast India and south peninsular India get good rainfall activity. Correlation coefficients between monthly LPS days over the different grids and monthly sub-divisional rainfall are computed to study the relationships. The performance of sub-divisional rainfall mostly related with the occurrence of LPS in certain grid- locations. The correlation field maps may give some useful information about rainfall performance due to LPS in a particular grid locations.

A forecasting aspect of thundersquall over Calcutta and its parameterisation during pre-monsoon season

Abstract: Severe thunderstorms accompanied by squalls are the most hazardous weather phenomena during pre-monsoon season in north-eastern region of India. An attempt has been made in this paper to study some parameters for forecasting thundersqualls over Calcutta (Airport) during pre-monsoon season. Parameterisation of thermodynamic components alongwith the synoptic support during thundersqualls over Calcutta has been discussed here. A forecasting aspect for propagation speed of thunderstorm cell at Calcutta in pre-monsoon season has been examined with respect to radar-echo positions, mid-level winds and convective available potential energy (CAPE). Occurrences of multiple thundersqualls over Calcutta Airport within a few hours’ interval have been discussed and examined through hodograph analysis, radar observations and synoptic situations.

Breaks in monsoon and related precursors

Abstract: A comprehensive analysis of eleven break monsoon situations that occurred during the period 1987 to 1997 have been attempted in the study. The various features like daily rainfall departures, wind anomalies and the satellite derived Outgoing Long wave Radiation (OLR) associated with the commencement/cessation of the break monsoon condition are studied with a view to identifying the precursors associate the break situation. The results reveal that there is progressive decrease of below normal rainfall departures 5 days prior to the actual break day in the latitude belts south of 20° N. During the period of the revival of the monsoon, the time section of the daily rainfall departures shows that the daily rainfall departure first starts becoming above normal in the southern most latitudinal belt 5° N to 10°N from the second day onwards after the cessation of the break. Similarly, the easterly anomalies in the zonal wind are first noticed in the southern latitude even 5 days prior to the starting of the break in the lower and middle troposphere. The maximum easterly anomalies in the lower and the middle troposphere move northwards upto 20° N. The composite latitudinal time section of OLR anomaly show a large area of negative OLR anomaly extending from 20°S to 10°N. The area is defined as the Southern. Hemispheric Convective Zone ( SHCZ). The negative OLR anomaly (10 Wm-2 is noticed around 5° S to 0° N. It increases to 20 Wm-2 on the second day of the break on the same latitudinal belt. The daily OLR anomaly pattern shows that the area of the negative OLR anomaly around the equatorial region increases with the approach of a break epoch. The forecasting aspects of the commencement / cessation of the break have been also discussed.

Determination of Cloud and Precipitation Characteristics in the Monsoon Region Using Satellite Microwave and Infrared Observations

Abstract: We have studied the cloud and precipitation features in the Indian summer monsoon region based on satellite microwave and infrared observations. Emphases are particularly given to the differences between stratiform and convective rains and between rains over land and over ocean. In the studied region, average rainfall rate of convective clouds is about 6 times higher than for stratiform clouds while the latter covers 4 to 5 times more area than the former. As a result, convective rains produce higher rain total than stratiform rains with a ratio of about 3 : 2. The difference between convective and stratiform rains is evident virtually by any satellite signatures – cloud top temperature, and microwave emission, scattering and combined signatures. Cloud top temperature appears no skill to reflect surface rainfall rates for stratiform rains while colder cloud top temperatures correspond to higher rainfall rates for convective clouds. As rainfall rate increases, microwave emission signature reaches saturation much quicker for stratiform rains than for convective rains. For convective rains, the rainfall rate – scattering signature relation shows a distinct difference between rains over land and over ocean. Corresponding to the same rainfall rate, the scattering signature over land is about twice as high as that over ocean. The mean vertical precipitation profiles showed that stratiform rains have a constant rainfall rate below freezing level and a sharp drop-off above, regardless over land or ocean. Convective rain profiles, on the other hand, often have the maximum rainfall rate below the freezing level, implying a significant growth of raindrops by warm microphysical processes, such as coalescence. It is also found that given the same surface rainfall rate, the amount of ice particles above freezing level is substantially greater for convective rains over land than over ocean, which explains the difference of scattering signatures between rains over the two different surface types. It is also demonstrated that the sub-pixel variability of rains is largely responsible for the mismatch between plane-parallel model simulations and actual satellite observations.

Comparison of evapotranspiration models

Abstract: Actual evapotranspiration of wheat crop during different year from 1978-79 to 1992-93 was measured daily in Varanasi, Uttar Pradesh using lysimeter. In this study three evapotranspiration computing models namely Doorenbos and Pruitt, Thornthwaite and Soil Plant Atmosphere Water (SPAW) have been used. Comparisons of these three methods show that the SPAW model is better than the other two methods for evapotraspiration estimation. In the present study the MBE (Mean-Bias-Error), RMSE (Root Mean Square Error) and t-statistic have also been obtained for better evaluations of a model performance.

Short term prediction of atmospheric temperature using neural networks

Abstract: In this paper, a neural network based forecasting model for the maximum and the minimum temperature for the ground level is proposed. A backpropagation method of gradient-decent learning in multi-layer perceptron (MLP) type of neural network with only one hidden layer is considered. This network consists of 25 input nodes and two output nodes. The network is trained with a varying number of nodes in the hidden layer using a set of training sample and each of them is tested with a set of test sample. It accepts previous two consecutive days information (such as pressures, temperatures, relative humidities, etc.) as inputs for the estimation of the maximum and the minimum temperature as output. The network with 20 or less neurons in the hidden layer is found to be "optimum" and it produces an error within ±2° C for 80% of test cases.

Observations of daytime surface energy balance in cloudy tropical conditions at Ile-Ife, Nigeria

Abstract: Daytime energy balance at the surface in cloudy tropical conditions for Ile-Ife; Nigeria (7°33'N, 4°34'E) is investigated based on a series of micrometeorological measurements performed in October/November of 1998. For the humid environment that it is (mixing ratio, 17 -25 g / kg), magnitudes of the latent heat flux were much larger than the values for the sensible heat. Of the morning hours the average value for the Bowen ratio obtained was 0.36, while for the afternoons it was 0.74. As the soil surface became dried up in the afternoons, magnitudes of both sensible heat and ground heat fluxes were found to be comparable. Fluctuations in the magnitudes of the terms of the surface energy balance correlated well to the cloud amount, degree of soil wetness, air temperature and humidity. But of all these factors, the variation in the amount of cloudiness appeared most dominant.

Intra-seasonal variation of surface air temperature in Nepal Himalayas

Abstract: Intra-seasonal variation of surface air temperature observed by the automatic weather station at Syangpoche in Khumbu region, Nepal Himalayas, is analyzed. In the monsoon season, temperature was nearly constant with large decrease in insolation due to monsoon clouds. On the other hand, large intra-seasonal variation existed in the winter with increase in temperature associated with passing synoptic scale high-pressure system which disturb local circulation pattern as well as decrease in temperature due to the nighttime strong radiative cooling under the condition of snow covers. Monsoon clouds and deep valley system caused unique surface temperature variation.

African monsoons, Part 2: Synoptic-scale wave disturbances in the intertropical convergence zone over north Africa

Abstract: In this part, the paper discusses several aspects of the origin, structure, development and movement of wave disturbances over the North African tropical zone during the northern summer. Analyzing the cases often actual wave disturbances which later in their life cycles developed into hurricanes over the Atlantic, it finds that though the horizontal and vertical shear of the mean zonal wind associated with the mid-tropospheric easterly jet over Africa satisfies the condition of dynamical instability under certain restrictive boundary conditions, it is the influence of a large-amplitude baroclinic wave in mid-latitude westerlies upon a stationary wave in the mountainous region of the east-central north Africa that appears to trigger the birth of a wave disturbance in the intertropical convergence zone over the Nile valley of Sudan between the Marra and the Ethiopian mountains. Physical processes likely to be important in the formation, development and movement of the disturbances are pointed out.

Prediction of potential and attainable yield of wheat : A case study on yield gap

Abstract: This study reports the role of field experimentation and system simulation in better quantifying the productivity of wheat crop, and examine how knowledge on potential productivity can improve the efficiency of the production system. When knowledge from field experimentation is utilised into crop weather simulation models, gap between actual, attainable and potential yield for a given environment can be determined and opportunities for yield improvement can be assessed. Results show that while actual district average yields show increasing trend, decreasing trend is noticed in potential and attainable yield. While the total and management yield gap is decreasing over time, research yield gap does not show any trend, it is nearly stagnant from early eighties to late nineties. The study reported here presents the advantage of simulation models to determine the yield gap against a variable annual yield potential for a agro-climatic region.

Short range SW monsoon rainfall forecasting over India using neural networks

Abstract: Feedforward Neural Networks are used for daily precipitation forecast using several test stations all over India. The six year European Centre of Medium Range Weather Forecasting (ECMWF) data is used with the training set consisting of the four year data from 1985-1988 and validation set consisting of the data from 1989-1990. Neural networks are used to develop a concurrent relationship between precipitation and other atmospheric variables. No attempt is made to select optimal variables for this study and the inputs are chosen to be same as the ones obtained earlier at National Center for Medium Range Weather Forecasting (NCMRWF) in developing a linear regression model. Neural networks are found to yield results which are atleast as good as linear regression and in several cases yield 10 - 20 % improvement. This is encouraging since the variable selection has so far been optimized for linear regression.

Energetics of zonal waves during different phases of monsoon

Abstract: Energetics of lower tropospheric zonal waves during onset, established and withdrawal phases of monsoon have been studied for 1994, 1995 and 1996. The analysis show that energetics of wave 0 over R1 (10°S-10°N), long waves (waves 1-2) over R2 (10°N - 30°S) and short waves (waves 3-10) over R3 (30° N - 50° N) influence the monsoon activity over India on intra-seasonal scale. The weekly analysis of the energetics of zonal waves indicates that the momentum transport of wave 0 over latitudinal belt L0 (12° S - 3° N), wave 1 over the belt L1(10° N - 15° N) and wave 2 over the belt L2 (33° N - 45° N) is related to all India rainfall on a weekly scale. Larger southward momentum transport of wave 0 over L0 and larger northward momentum transport of wave 1 over L1 and wave 2 over L2 enhance the monsoon activity over India.

Climatological characteristics of sea breeze parameters at Chennai

Abstract: Several sea breeze parameters such as time of onset, withdrawal, duration, depth, variation with height, direction etc. have been derived and studied for Chennai city and Chennai AP observatories in this study, which has been based on a large data base for the period March-October,1969-83. The monthly and sub monthly values of several sea breeze parameters have been derived. By invoking the concept of superposed epoch analysis the important role played by sea breeze in modulating diurnal variation of surface temperature and relative humidity has been established. The sea breeze at Chennai has been shown to be shallow with a depth of under 1 km. Modal directions of sea breeze and its normal speed have been derived.

Multi layer perceptron model in pattern recognition of surface parameters during pre-monsoon thunderstorm

Abstract: The concept of Multi Layer Perceptron and Fuzzy logic is introduced in this paper to recognize the pattern of surface parameters pertaining to forecast the occurrence of pre-monsoon thunderstorms over Kolkata (22 ° 32¢ , 88 ° 20¢ ). The results reveal that surface temperature fluctuates significantly from Fuzzy Multi Layer Perceptron (FMLP) model values on thunderstorm days whereas on non-thunderstorm days FMLP model fits well with the surface temperature. The results further indicate that no definite pattern could be made available with surface dew point temperature and surface pressure that can help in forecasting the occurrence of these storms.

Recent trends in climate of Bangalore

Abstract: The linear trends in the monthly, seasonal and annual mean maximum temperature, minimum temperature, average temperature, diurnal range of temperature, rainfall, relative humidities at 0830 & 1730 hr IST of Bangalore city and airport have been analysed based on the data for the period from 1960-95. The variation in surface wind over Bangalore during above period has also been studied to find out impact of urbanisation on weather parameters. It is found that Bangalore city is becoming warmer in terms of mean maximum & mean minimum temperatures. Rate of increase is significantly higher over Bangalore city (central observatory) than that over airport during winter months. Similarly the rising trend of average temperature of Bangalore city is higher than of Bangalore airport during October to April being significantly so during winter season. Also the diurnal range of temperature of Bangalore is becoming larger in winter months with the rising trend being higher over Bangalore city than over airport. Even though rainfall does not show any significant trend, the rising trend during monsoon & falling trend during post monsoon season over Bangalore city are higher than that of Bangalore airport. Also though both Bangalore city & airport show maximum rising trend in mean relative humidity at 0830 hr IST during winter, the rate of rise is less over Bangalore city. Similarly though the relative humidity at 1730 hr IST shows decreasing trend during all the seasons, the rate of decrease is less over Bangalore city for all seasons except post monsoon season. The mean maximum, minimum and average temperatures and relative humidities show cyclic variation of their monthly trend coefficients during the year.

Atmospheric boundary layer during northeast monsoon over Tamilnadu and neighbourhood - A study using TOVS data

Abstract: Thermodynamic structure of atmospheric boundary layer during October - December covering southwest and northeast monsoon activities over interior Tamilnadu (ITN), coastal Tamilnadu (CTN) and adjoining Bay of Bengal (BOB) has been studied using TIROS Operational Vertical Sounder (TOVS) data of 1996-98. Heights of neutral stratified mixed layer, cloud layer and planetary boundary layer (PBL) have been estimated through available standard pressure level data. Highest PBL occurs during active northeast monsoon. Cloud layer thickness during weak northeast monsoon over interior Tamilnadu is significantly higher than that over coastal Tamilnadu and also over Bay of Bengal. Convective stability (instability) of the atmosphere in 850-700 hPa layer is associated with weak / withdrawal (active) phase of northeast monsoon. One of the plausible reasons for subdued rainfall activity during weak northeast monsoon over interior Tamilnadu could be convective instability seen over this region in 850-700 hPa layer. But the same is absent in CTN and BOB where no rainfall activity exists during weak monsoon phase. Virtual temperature lapse rate in 850-700 hPa layer exceeding (less than) 6oK/km is associated with active (weak) phase of northeast monsoon over the interior, coastal Tamilnadu and Bay of Bengal.

DMSP-SSM/I retrieval of proper surface winds during monsoon depression

Abstract: Recently developed various global microwave algorithms for DMSP-SSM/I satellite data are used for the estimation of surface winds over the Indian ocean. Sea surface wind speeds from these algorithms are compared with sea surface wind speeds reported by coincidental Minicoy island (lowest height 2 m a.s.l.) station over the Arabian sea. A statistical comparison of these algorithms is made in terms of rms error, correlation coefficient, bias and standard deviation. Algorithm of Petty showed best results in the comparison. On the basis of this algorithm a notable characteristic feature such as acquiring of large area of strong surface winds (12-15 ms-1) to the south of dipping of monsoon trough in head Bay and then encircling of these winds during further development of low and depression (22-27 July 1992) is observed. This complete life cycle monitoring assessment of monsoon depression in respect of surface winds based on DMSP-SSM/I satellite data encourages to utilise our IRS-P4 (Oceansat-1) satellite data at different frequencies to emerge more details of various weather systems over the Indian region.

Impact of ERS-2 Scatterometer wind data on Global Analysis-Forecast system

Abstract: The near surface scatterometer wind data from the European remote sensing satellite ERS-2 of European space agency(ESA) became available at NCMRWF on real time basis since February 1997. An attempt has been made to assimilate this data in the global data assimilation system(GDAS) operational at NCMRWF after proper quality control to study its impact on the analysis as well as on medium range weather forecast over the tropics. For this purpose the GDAS was run for 15 days (27 May to 10 June 1998). The impact has been examined through circulation characteristics and various objective scores. The study revealed that with proper quality control the scatterometer wind data can be assimilated in real time basis, resulting in an overall improvement in performance of the analysis-forecast system.

Estimation of monsoon wind characteristics in India

Abstract: A detailed statistical analysis of monthly average wind speed data of monsoon period (June-September) for the year 1921-90 for 57 stations spread all over India have been reported. Probability densities, average wind speeds, standard deviations, kurtosis and skewness of wind speed frequency distribution for each station have been worked out. Histograms depicting relative frequency distribution of average wind speeds have also been prepared. It is observed that the different histograms do not exhibit any similarity among themselves indicating thereby that no single distribution is uniformly applicable for all the stations. It is also seen that the average wind speeds during monsoon period over major part of India varies from 7 to 14 kmph. Further, at most of the stations average monsoon wind speed is generally higher than average annual wind speeds. It is also noted that most of the time the wind speed exceeds 10 kmph in coastal regions of Gujarat and southern parts of the peninsular India. The information generated is of multi fold application such as (i) Identification of sites suitable for installation of Wind Energy Conversion Systems (ii) Development of Driving Rain Index and (iii) Design of buildings for creating comfortable environment indoors.

Antarctic ozone recovery

Abstract: Since 1976, and more so since 1985, the Antarctic ozone level has suffered considerable depletion (termed as Antarctic ozone hole), attributed to the destructive effects of CFC compounds leaking into the atmosphere from man-made gadgets. The 12-month running means of South Pole Dobson ozone (monthly means, upto 1999 end only) were subjected to spectral analysis, which showed considerable, significant amplitudes for QBO (Quasi-biennial, 2-3 years) and QTO (Quasi-triennial, 3-4 years) oscillations, with a total range of 20-30 DU. When subtracted from the original values, a fairly smooth variation was seen, with a decrease from ~260 DU in 1986 to ~230 DU in 1996 (~12% decrease in 12-month running means), and an almost steady level thereafter. Thus, the net ozone variation at South Pole consists of two parts, (i) a long-term monotonically downward trend upto 1996 and a steady level thereafter and (ii) a superposed QBO-QTO oscillation. The chemical destruction effect is not likely to disappear soon, and may even increase if greenhouse effects, major volcanic eruptions or enhanced stratospheric cooling intervene. If the long-term level (i) remains steady, an extrapolation of the QBO-QTO patterns indicates that the ozone level is due for an increase from about 1999 end to about 2001 beginning. The purpose of the present analysis is to point out that, if such an increase of 20-30 DU occurs, it should not be misinterpreted as due to a decrease in chemical destruction, which scientists are eagerly awaiting due to the indication of a reduction in the halogen load in recent years due to adherence to the Montreal Protocol. After one or two years (in 2002), the extrapolated QBO-QTO oscillation may bring down the ozone level back again to the 1999 end level, and the apparent recovery may turn out to be a false signal.

Quasi-biennial and quasi-triennial oscillations in the growth rates of atmospheric chlorofluorocarbons 11 and 12

Abstract: The 12-monthly running means of CFC-11 and CFC-12 were examined for 1977-1992. As observed by earlier workers, during 1977-1988, there was a rapid, almost linear increase of these compounds, ~70% in the northern and ~77% in the southern hemisphere. From 1988 up to 1992, growth rates were slower, more so for CFC-11 in the northern hemisphere. Superposed on this pattern were QBO, QTO (Quasi-Biennial and Quasi-Triennial Oscillations). A spectral analysis of the various series indicated the following. The 50 hPa low latitude zonal wind had one prominent QBO peak at 2.58 years and much smaller peaks at 2.00 (QBO) and 5.1 years. The Southern oscillation index represented by (T-D), Tahiti minus Darwin atmospheric pressure, had a prominent peak at 4.1 years and a smaller peak at 2.31 years. CFC-11 had only one significant peak at 3.7 years in the southern hemisphere, roughly similar to the 4.1 year (T-D) peak. CFC-12 had prominent QBO (2.16-2.33 years) in both the hemispheres and a QTO (3.6 years) in the southern hemisphere. For individual locations, CFC-11 showed barely significant QBO in the range (1.95-3.07 years), while CFC 12 showed strong QBO in the range (1.86-2.38 years). The difference in the spectral characteristics of CFC-11 and CFC 12 time series is attributed to differences in their lifetimes (44 and 180 years), source emission rates and transport processes.

Influence of meteorological parameters on performance of rainfed cropping systems

Abstract: Rainfall, its distribution along with distribution of temperature. relative humidity (RH), bright sunshine hours (SSH) suggest the possible growing season and crop performance in a given area. Field experiments on five economically feasible, sustainable, rainfed crop sequences viz. fallow (i.e. no crop) – rice-lentil, jute-rice-lentil, direct seeded rice-rice-lentil, mungbean-rice-lentil and sesame-rice-lentil were conducted at Kalyani Farm, W.B., during 1989-91. Mean monthly meteorological parameters viz. rainfall, potential evapotranspiration (PET), SSH, temperature (max. and min.) and RH (at 0700 and 1400 hrs LMT) were obtained from selected agrometeorological observatories (viz. Chinsurah, Haringhata and Barrackpore), adjacent to the Kalyani Farm located in Gangetic alluvial region. The relative yield performance of crops and sequences as influenced by meteorological parameters were studied. In Gangetic alluvial region early rain, moderate to high temperature with high RH during April/May resulted in good pre-kharif crop establishment. Heavy, well distributed precipitation during monsoon months along with moderate temperature and very high RH showed scope for rainfed transplanted kharif rice as the pivot of crop rotation. Kharif rice yields were high especially after jute or mungbean. Profile stored residual moisture along with low rainfall, low temperature and high RH during rabi season resulted in good performance of lentil. Among the five sequences studied, performance of' jute-rice-lentil and mungbean-rice-lentil were the best with sustainable production and net return.

Water consumption of cotton in the semi arid tracts of India

Abstract: In the present study, evapotranspiration and other agrometeorological data for three different locations, viz., Akola. Bellary and Kovilpatti have been utilized to understand consumptive use and related aspects of cotton. Ratios of evapotranspiration to potential evapotranspiration (ET/PET) and evapotranspiration to total shortwave radiation (ET/Rs) increase gradually as the vegetative cover develops and shows year to year variation at same location. The energy summation indices have been worked out for all the three stations which indicate that the total yields are more dependent on consumptive water use by crop rather than energy summation indices.. The water use efficiency (WUE) of cotton crop also reveals wide variations in time and space.