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Construction of Vertical Wind Profile from Satellite-Derived Winds for Objective Analysis of Wind Field

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Advances in Atmospheric Sciences 1992年第2期9卷 237-246页

作者： P.N.Mahajan D.R.Talwalkar S.Nair S.Rajamani indian institute of tropical meteorology Pune-411008Indian Institute of Tropical Meteorology Pune-411008Indian Institute of Tropical Meteorology Pune-411008Indian Institute of Tropical Meteorology Pune-411008

During summer Monex-79, a variety of observing systems viz. research ships, research aircrafts, constant pressure balloons and geostationary satellite etc. were deployed, besides the regular conventional observations. The purpose of these additional systems was to make the best possible data for the studies on various aspects of monsoon circulation. The present study is aimed at the construction of vertical wind profile using cloud motion vectors obtained from GOES (I-O) satellite and to examine whether the constructed wind profiles improves the representation of the monsoon system, flow pattern etc. in the objective analysis. For this purpose, climatological normals of the wind field are considered as the initial guess and the objective analyses of the wind field are made with, first using only data from conventional observations over land areas, subsequently including the constructed winds from cloud motion vectors. These analyses are then compared with the standard analyses of wind field obtained from Quick Look Atlas by T. N. Krishnamurti et al. (1979).It is inferred that satellite estimated mean wind profiles show good agreement with the mean wind profiles of the research ships with RMS errors less than 5 mps below 500 hPa and less than 8 mps above 500 hPa. It is further inferred that the inclusion of constructed winds shows a positive impact on the objective analysis and improvement is seen to be more marked in the data-sparse region of the Arabian sea. Analyses which include the constructed winds show better agreement with the standard analysis, than the analyses obtained using only conventional winds. Thus, results of our study suggest that the wind profiles constructed using cloud motion vectors are of potential use in objective analysis to depict the major circulation features over the indian region.

关键词： Construction of Vertical Wind Profile from Satellite-Derived Winds for Objective Analysis of Wind Field Wind

Use of Surface Observations to Estimate Upper Air Humidity for the Objective Analysis of Relative Humidity over indian Region

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Advances in Atmospheric Sciences 1990年第4期7卷 491-501页

作者： S.K.Sinha D.R.Talwalkar S.G.Narkhedkar P.L.Kulkarni S.Nair S.Rajamani indian institute of tropical meteorology Pune-411008 India Indian Institute of Tropical Meteorology Pune-411008 IndiaIndian Institute of Tropical Meteorology Pune-411008 IndiaIndian Institute of Tropical Meteorology Pune-411008 IndiaIndian Institute of Tropical Meteorology Pune-411008 IndiaIndian Institute of Tropical Meteorology Pune-411008 India

In the present study objective analyses of relative humidity (RH) at surface and at the levels of 850, 700 and 500 hPa have been made using Gandin's (1963) optimum interpolation scheme. As the horizontal resolution of the radiosonde stations is rather inadequate for upper air humidity analysis, a scheme has been developed, following Rasmussen (1982) to estimate the upper air RH from the surface observations like surface RH, present weather and cloud cover. The relative humidities at the levels 850, 700 and 500 hPa were related to the surface observations through three separate regression relations. The RH values at 850, 700 and 500 hPa levels were estimated from the surface RH, cloud coverage and present weather using the above regression relations and subsequently the objective analyses at 00 GMT for the period from 4 July to 8 July 1979, were made using these estimated data along with the observed radiosonde data. Objective analyses were also made for the same period using only the radiosonde data for comparison to study the impact of those estimated data. Root mean square errors were computed for all the five days by interpolating RH at the observing stations from the objectively analysed field and comparing them with the actually observed RH to examine how best the analyses (with and without estimated data) fitted the observations. Lastly they were compared with satellite cloud pictures. This study shows that the estimated upper air RH values have positive impact on the analysis of upper air RH and could be used over radiosonde data sparse region and even over oceanic regions.

关键词： In RH over

Temperatures and Winds over tropical Middle Atmosphere during Two Contrasting Summer Monsoons, 1975 and 1979

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Advances in Atmospheric Sciences 1989年第3期6卷 325-334页

作者： B.K.Mukherjee C.P.Kulkarni K.Indira K.K.Dani indian institute of tropical meteorology Pune-411005IndiaIndian Institute of Tropical MeteorologyPune-411005IndiaIndian Institute of Tropical MeteorologyPune-411005IndiaIndian Institute of Tropical MeteorologyPune-411005India

Using the monthly geopotential heights and winds for 700 and 200 hPa for India during July and August, and the weekly M-100 Soviet rocketsonde temperature and wind data for Thumba (8.5 ° N, 76.9 ° E) during the last week of June and the first week of September for the two contrasting summer monsoon years 1975 (a very strong monsoon year) and 1979 (a very weak monsoon year), a study has been made to examine the mean circulation features of the troposphere over India, and the structures of the temperatures and the winds of the middle atmosphere over Thumba. The study suggested that the axis of the monsoon trough (AMT) at 700 hPa shifted southward in 1975 and northward towards the foothills of the Himalayas in 1979, from its normal position. Superimposed on the low-pressure area (AMT) at 700 hPa, a well-defined divergence was noticed at 200 hPa over the northern India in *** mean temperatures at 25,50 and 60 km (middle atmosphere) over Thumba were cooler in 1975 than in 1979. While a cooling trend in 1975 and warming trend in 1979 were observed at 25 and 50 km, a reversed picture was noticed at 60 km. There was a weak easterly / westerly (weak westerly phase) zonal wind in 1975 and a strong easterly zonal wind in 1979. A phase reversal of the zonal wind was observed at 50 km. A tentative physical mechanism was offered, in terms of upward propagation of the two equatorially trapped planetary waves i.e. the Kelvin and the mixed Rossby-gravity waves, to explain the occurrence of the two spells of strong warmings in the mesosphere in 1975.

关键词： over In and 1979 Temperatures and Winds over tropical Middle Atmosphere during Two Contrasting Summer Monsoons

Some Experiments with Multivariate Objective Analysis Scheme of Heights and Winds Using Optimum Interpolation

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Advances in Atmospheric Sciences 1992年第4期9卷 431-440页

作者： S.K.Sinha S.G.Narkhedkar D.R.Talwalkar S.Rajamani indian institute of tropical meteorology Pune 411008 IndiaIndian Institute of Tropical Meteorology Pune 411008 IndiaIndian Institute of Tropical Meteorology Pune 411008 IndiaIndian Institute of Tropical Meteorology Pune 411008 India

A two-dimensional, multitvariate objective analysis scheme for simultaneous analysis of geopotential height and wind fields has been developed over indian and adjoining region for use in numerical weather prediction. The height-height correlations calculated using daily data of four July months (1976-1979), are used to derive the other autocorrelations and cross-correlations assuming geostropic relationship. A Gaussian function is used to model the autocorrelation function. Since the scheme is multivariate the regression coefficients (weights) are *** the equator, the geostrophic approximation relating mass and wind is decoupled in a way similar to Bergman (1979). The objective analyses were made over indian and adjoining region for 850, 700, 500, 300 and 200 hPa levels for the period from 4 July to 8 July 1979, 12 GMT. The analyses obtained using multivariate optimum interpolation scheme depict the synoptic situations satisfactorily. The analyses were also compared with the FGGE analyses (from ECMWF) and also with the station observations by computing the root mean square (RMS) errors and the RMS errors are comparable with those obtained in other similar studies.

关键词： In Some Experiments with Multivariate Objective Analysis Scheme of Heights and Winds Using Optimum Interpolation

Aircraft Observations of Electrical Conductivity in Warm Clouds

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Advances in Atmospheric Sciences 1993年第1期10卷 95-102页

作者： P.Ernest Raj P. C. S. Devara A. M. Selvam A. S. R. Murty indian institute of tropical meteorology Pune 411008 IndiaIndian Institute of Tropical Meteorology Pune 411008 IndiaIndian Institute of Tropical Meteorology Pune 411008 IndiaIndian Institute of Tropical Meteorology Pune 411008 India

Aircraft observations of electrical conductivity and cloud microphsical, dynamical and other electrical parameters were made in warm stratocumulus and cumulus clouds forming during the summer monsoon seasons (June-September) of 1983 and 1985 in the Deccan Plateau region, India. A Gerdien type cylindrical condenser was used for the measurement of electrical conductivity. The variations in the electrical conductivity are observed to be closely associated with the updrafts and downdrafts in the cloud, liquid water content, cloud droplet charge and corona discharge current. The value of electrical conductivity in warm clouds is found to be in the order of 10-12 ohm-1 m-1 which is two orders higher than that observed in clear-air at cloud-base levels in some regions by other *** static electricity concepts predict reduced conductivity values inside clouds. Cloud electrical conductivity measurements, particularly in warm clouds are few and the results are contradictory. The recently identified mechanism of vertical mixing in clouds lends support to convective charge separation mechanism with inherent larger than clear-air values for cloud electrical conductivity and therefore consistent with the measurements reported herein.

关键词： Aircraft Observations of Electrical Conductivity in Warm Clouds

Short－term　Climatic　Fluctuations　in　North　Atlantic　Oscillation　and　Frequency　of　Cyclonic　Disturbances　over　North　indian　Ocean　and　Northwest　Pacific

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Advances in Atmospheric Sciences 1995年第3期12卷 371-376页

作者： S. S. Dugam S. B. Kakade indian institute of tropical meteorology

A relationship between mean sea level pressure gradient between Azores High (AH) and Icelandic Low (IL) hereafter called North Atlantic Oscillation Index (NAOI) and the frequency of cyclonic disturbances over North indianOcean is investigated using 98 years of date (1891-1988). The analysis is carried out on monthly, seasonel, annual anddecadal scales. Similar studies are also done for North West Pacific ocean cyclonic disturbances. It is nohced that thenumber of cyclonic disturbances over North indian Ocean during monsoon season (June-September) as well as onannual scale is significantly correlated with NAOI. However for pre (April-May) and post (October-November-December) monsoon seasons frequency of cyclonic disturbances do not bear similar relationship with NAOI. Thestudy also shows that decadal scale variability of cyclonic disturbances during the summer monsoon over North indian Ocean has a remarkable correspondence with the decadal variability of NAOI.

关键词： North Atlantic Oscillation Cyclonic disturbances

A Hydrometeorological Analysis of the Severe Rainstorm of 20-22 September 1900 over the Gangetic West Bengal

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Advances in Atmospheric Sciences 1993年第1期10卷 113-120页

作者： P. R. Rakhecha B. N. Mandal A. K. Kulkarni R. B. Sangam indian institute of tropical meteorology Pune 411008 IndiaIndian Institute of Tropical Meteorology Pune 411008 IndiaIndian Institute of Tropical Meteorology Pune 411008 IndiaIndian Institute of Tropical Meteorology Pune 411008 India

A hydrometeorological study is made of the September, 1900 severe rainstorm which led up to the record rainfalls over Gangetic West Bengal with subsequent disastrous flooding in the Damodar and the Hooghly rivers. The spatial extent of the rainstorm for different durations has been examined by constructing the isohyetal patterns based on rainfall records of stations affected by the storm. Areal rainfalls for 1,2 and 3-day periods are calculated and the values have been compared with similar values from other major rainstorms of the region. The comparison revealed that the September, 1900 rainstorm was the heaviest for 1,2 and 3-day durations for all the areas. The storm contributed rainfalls of 33.0 cm, 52.0 cm and 62.0 cm over an area of 10,000 km2 in 1,2 and 3 days respectively. This rainstorm could, therefore, be considered as an important input in flood and design storm studies in the Gangetic West Bengal region. A relationship between point to areal rainfall has also been developed with a view to evaluate areal PMP estimates.

关键词： A Hydrometeorological Analysis of the Severe Rainstorm of 20-22 September 1900 over the Gangetic West Bengal over West

Some　Unique　Characteristics　of　Atmospheric　Interannual　Variability　in　Rainfall　Time　Series　over　India　and　the　United　Kingdom

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Advances in Atmospheric Sciences 1995年第3期12卷 377-385页

作者： A. Mary Selvam J. S. Pethkar M. K. Kulkarni indian institute of tropical meteorology

Continuous periodogram analyses of two 50-years (1871-1920 and 1936-1985) of summer monsoon rainfallover the indian region and one 84-years set (1893-1976) of winter half-year rainfall over England and Wales showthat the power spectra of disparate rainfall regimes follow the universal and unique inverse power law form of the statistical normal distribution with the percentage contribution to total variance representating the eddy probability corresponding to the normalized standard deviation equal to [(log L / log T50)-1] where L is the Period in years and T50the period up to which the cumulative percentage contribution to total variance is equal to 50. The above results areconsistent with a recently developed non-deterministic cell dynamical system model for atmospheric flows. The implications of the above results for prediction of interannual variability of rainfall is discussed.

关键词： Interannual variability in rainfall Chaos Fractals Self-organized criticality

Role　of　Triad　Kinetic　Energy　Interactions　for　Maintenance　of　Upper　Tropospheric　Low　Frequency　Waves　during　Summer　Monsoon　　1988

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Advances in Atmospheric Sciences 1996年第1期13卷 91-102页

作者： D. R. Chakraborty N. K. Agarwal indian institute of tropical meteorology

In order to determine nonlinear energy exchanges into individual triad interactions in the frequency domain,spectral formulas are derived by use of the cross-spectral technique. First time attempt has been made to understandthe problem of maintenance of low frequency waves for tropical weather system by using this *** TOGAbasic level ill daily wind analyses on a 2.5 degree square grid around the global zone from 20°S-30°N at 200 hpa for92-day periods covering June, July and August of 1988 are used. Kinetic energy is gained at high frequencies and lostat low *** the planetary scale dynamics over tropics, barotropic nonlinear energy transfer plays a *** frequency wave of period 45 day loses maximum amount of energy when it interacted with frequencies ofperiods 92 day and 30 day.45 day cycle is also the main source of energy for other frequencies. Distrubances of periodl 5 day gain maximum amount of *** major contribution comes from the triad interaction of the frequencies.North of 20'N low frequency waves of period 30 to 92--day gain energy through nonlinear triadinteraction with the maximum gain at 22.5'N. The study may help to investigate the rapid loss of predictability of lowfrequency modes over tropics.

关键词： Cross spectral technique Low frequency mode