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  • 1
    Electronic Resource
    Electronic Resource
    A Study on the Performance of the NCMRWF Analysis and Forecasting System During Asian Summer Monsoon: Thermodynamic Aspects (1999)
    Springer
    Pure and applied geophysics 154 (1999), S. 141-162 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Asian summer monsoon, systematic errors, temperature, moisture, heat budget, moisture budget.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —The thermodynamic characteristics of the Asian summer monsoon are examined with a global analysis-forecast system. In this study, we investigated the large-scale balances of heat and moisture by making use of operational analyses as well as forecast fields for June, July and August (JJA), 1994. Apart from elucidating systematic errors in the temperature and moisture fields, the study expounds the influence of these errors on the large-scale budgets of heat and moisture over the monsoon region. The temperature forecasts of the model delineate predominant cooling in the middle and lower tropospheres over the monsoon region. Similarly, the moisture forecasts evince a drying tendency in the lower troposphere. However, certain sectors of moderate moistening exist over the peninsular India and adjoining oceanic sectors of the Arabian Sea and Bay of Bengal.¶The broad features of the large-scale heat and moisture budgets represented by the analysis/forecast fields indicate good agreement with the observed aspects of the summer monsoon circulation. The model forecasts fail to retain the analyzed atmospheric variability in terms of the mean circulation, which is indicated by underestimation of various terms of heat and moisture budgets with an increase in the forecast period. Further, the forecasts depict an anomalous diabatic cooling layer in the lower middle troposphere of the monsoon region which inhibits vertical transfer of heat and moisture from the mixed layer of the atmospheric boundary layer to the middle troposphere. In effect, the monsoon circulation is considerably weakened with an increase in the forecast period. The treatment of shallow convection and the use of interactive clouds in the model can reduce the cooling bias considerably.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050225
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  • 2
    Electronic Resource
    Electronic Resource
    Assessment of quality and impact of full resolution TOVS temperature profile data on the operational global data assimilation-forecast system of India (1998)
    Springer
    Meteorology and atmospheric physics 68 (1998), S. 197-212 
    Details
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary TOVS temperature profile data (SATEM) at its full resolution (85 km) has now become available in India on experimental basis. An attempt is made in this study to examine the quality and impact of this on the medium range forecasts over India and neighbourhood. For this purpose, a seven day period starting from 15 March 1996 is chosen to study the impact of the data on the global analysis-forecasting system operational in India. Though one week data is utilized for the impact study, the complete data of march 1996 is used for examining quality, representativeness and consistency of the retrievals. In the operational system of the National Centre for Medium Range Weather Forecasting (NCMRWF), all types of data, including coarse resolution (500 km) global TOVS retrievals-coarse grid SATEM (CGS) data, received on GTS at hourly intervals are used in the assimilation cycle. For the present study the assimilation cycle is repeated for the above period by including high resolution data over the geographical regions covered by the New Delhi's high resolution picture transmission (HRPT) station and simultaneously removing coarse resolution SATEM data. The analysis and forecast fields thus generated are compared with the corresponding operational archives. The impact of the data is examined in terms of various objective scores and through circulation characteristics. The study reveals that the quality of high resolution SATEM (HRS) data is satisfactory and is such that it can be utilized in the global data assimilation system on real-time basis. A general improvement in the RMSE and ACC scores of the medium range forecasts is found over the data void equatorial sectors of the Indian Ocean after the incorporation of the HRS data fields in the assimilation cycle. With regard to a typical easterly wave activity of moderate intensity during the period of experimentation a marginal modulation in low level vorticity and divergence forecasts is found to be improving the precipitation magnitudes over the south peninsular India as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01030211
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  • 3
    Electronic Resource
    Electronic Resource
    A study on the distinct features of the Asian summer monsoon during the years of extreme monsoon activity over India (1996)
    Springer
    Meteorology and atmospheric physics 59 (1996), S. 173-183 
    Details
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary In this paper, interseasonal characteristics of the Asian summer monsoon in the years of 1987 and 1988 are studied as 1987 is characterized by a large deficiency of monsoon rainfall (drought) and that of 1988 by a large excess monsoon rainfall (flood) over India. In order to compare the similarities and differences seen in the large scale dynamics and energetics of the Asian summer monsoon during the years of extreme monsoon activity, uninitialized analyses (12 Z) of the European Centre for Medium Range Weather Forecasts (ECMWF), U.K. are utilized in this study for the summer monsoon seasons of 1987 and 1988. It is found that the excess rainfall season (1988) is characterized by much stronger tropical easterly jet (TEJ) associated with the upper tropospheric easterlies and the East African low level jet (Somali Jet) associated with lower tropospheric westerlies. Such a feature mainly determines the strength of the reverse Hadley circulation which normally covers the South Asian continent during the northern summer. Further, the energetics of the TEJ show that the monsoon of 1988 has comparatively stronger zones of kinetic energy flux divergence (convergence) at its entrance (exit) regions. These zones of kinetic energy flux divergence are largely maintained by the adiabatic processes over the strong kinetic energy flux divergence zones over the Bay of Bengal and east central Arabian Sea as compared to that of 1987. Apart from this, both the zonal and meridional components of the ageostrophic flows are found to be stronger during 1988 monsoon season. Analysis of the vertically integrated thermodynamical features of the monsoon indicate that the monsoon of 1988 was characterized by an excess import of heat and moisture into the monsoon atmosphere as compared to that of 1987. Further, from the quantitative estimation of certain significant heat and moisture budget parameters during the contrasting monsoon seasons of 1987 and 1988, it becomes evident that considerable differences exist in the quantities of adiabatic production of heat energy, diabatic heating and the moisture source/sink.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01030142
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  • 4
    Electronic Resource
    Electronic Resource
    Objective determination of onset, advancement and withdrawal of the summer monsoon using large-scale forecast fields of a global spectral model over India (1996)
    Springer
    Meteorology and atmospheric physics 61 (1996), S. 137-151 
    Details
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary In this study, a detailed examination on the evolution of summer monsoon onset over southern tip of the Indian peninsula, its advancement and withdrawal over the Indian sub-continent is carried out by utilizing the analysis/forecast fields of a global spectral model for Monsoon-1995. The data base used in this study is derived from the archives of global data assimilation and forecasting system of NCMRWF, India, valid for 00UTC at 1.5° latitude/longitude resolution for the summer monsoon period of 1995. By utilizing the analyses and forecast fields, and the established knowledge of the Indian monsoon, objective criteria are employed in this study for determining the onset, advancement, and withdrawal of the monsoon. It is found that all the major characteristics of Monsoon-1995 are captured well by the analysis-forecast system even though the criteria adopted in this study are more objective and different in nature as compared to the conventional procedures. The onset date of monsoon over the southern tip of the Indian peninsula as determined by the dynamical onset procedure is found to be matching well with the realized date. Further, the evolution of monsoon onset characteristics over the Arabian Sea both in the analyses and forecasts is found to be in good agreement with the earlier studies. However, the magnitudes of net tropospheric moisture build-up and tropospheric temperature increase differ with respect to analyses and corresponding forecast fields. In addition, all important characteristics of the advancement and withdrawal of monsoon over the Indian sub-continent viz. stagnation, revival etc., are brought out reasonably well by the analysis and forecast system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01025702
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  • 5
    Electronic Resource
    Electronic Resource
    Intercomparison of the characteristic features of the southwest monsoon over india as reproduced in the mean monthly analyses and forecasts of some operational NWP centres during 1995 (1999)
    Springer
    Meteorology and atmospheric physics 69 (1999), S. 157-178 
    Details
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary An intercomparison of the characteristic features of the Indian summer monsoon has been carried out for the monsoon months (June to September) of 1995 using the mean monthly analyses/forecasts from the operational centres of ECMWF, JMA, UKMO and NCMRWF. This exercise was undertaken to determine how well the large scale monsoon features over India were reproduced in the operational output in 1995 and also to assess the performance of the NCMRWF assimilation/forecast system. For this purpose, precipitation, mean sea level pressure, circulation features in the lower (850 hPa) and upper (200 hPa) troposphere, mid-tropospheric (500 hPa) temperature, and latent heat flux were examined. It is found that all the dominant features of the Indian summer monsoon are fairly well represented in the analysis and medium range forecasts of the ECMWF, JMA and UKMO. The NCMRWF output agrees well with those from other centres except for a sharp gradient in precipitation across the west coast which was not captured well in the forecasts due to the relatively coarse horizontal resolution of the model compared to that used at other operational centres. Other important features of the southwest monsoon, like the heat low over the northwestern part of the country, the lower level westerly jet and upper level easterly jet etc. are found to be reasonably well represented in the output of all operational centres. The JMA analyses and forecasts possessed greater levels of moisture compared to the NCMRWF output possibly due to the synthetic moisture information used at JMA. The evolution characteristics of the summer monsoon onset over the southern tip of India are found to be comparable in the output of JMA and NCMRWF.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01030419
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  • 6
    Electronic Resource
    Electronic Resource
    A study on the systematic errors of the tropical forecasts: Influence of physical processes (1995)
    Springer
    Meteorology and atmospheric physics 55 (1995), S. 151-166 
    Details
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary In this paper, an attempt is made to examine the influence of the physical forcings of an atmospheric general circulation model (AGCM) in the reduction of the systematic errors of the tropical forecasts. A number of major modifications in the parameterization of physical processes were carried out in the operational forecasting system of the European Centre for Medium Range Weather Forecasts (ECMWF) during the period 1984–88 largely in an attempt to reduce the conceptual weaknesses in their formulation. A large number of studies (Slingo et al., 1988; Tiedtke et al., 1988; etc) have demonstrated the positive impact on the reduction of tropical forecast errors to various changes in the treatment of physical processes in the ECMWF model. Keeping in view of these facts, the evaluation of the systematic errors of the ECMWF tropical forecasts is carried out for a period prior to the incorporation of major modifications in the parameterization of physical processes (1984) and corresponding period after such major changes are implemented in the operational AGCM of ECMWF (1988). The paper describes a detailed comparison of the tropical forecast errors for summer monsoon seasons (June-August [JJA]) of 1984 and 1988 in order to bring out the impact on tropical simulation of various improvements in the treatment of physical processes. The results demonstrate a dramatic reduction in the systematic errors of the tropical circulation together with an enhancement of the hydrological cycle to a realistic climatological level with the incorporation of major changes in the treatment of physical processes. Similar improvements are also observed in the winter simulation. In spite of major improvements in the simulation of tropical circulation, the nature of the tropical systematic errors of the ECMWF AGCM, however, remains unchanged. Thus, the inference of the study indicates the requirement of a new approach to the problem of parameterization of physical processes particularly, convection, radiation, boundary layer and their interactions for further reduction of the tropical forecast errors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01029824
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  • 7
    Electronic Resource
    Electronic Resource
    Mean dynamical characteristics of the Asian summer monsoon with a global analysis — Forecast system (1998)
    Springer
    Meteorology and atmospheric physics 68 (1998), S. 57-77 
    Details
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary The dynamical characteristics of Asian summer monsoon are examined with a global spectral model. In addition to the seasonal circulation features, the large scale budgets of kinetic energy, vorticity and angular momentum are examined making use of mean analysis and forecast fields (upto day 5) for summer season comprising June, July and August, (JJA) 1994. Apart from elucidating the systematic errors over the monsoon region, the study expounded the influence of these errors on associated dynamics. The significant errors in the low level flow (850 hPa) evince (i) weakening of south easterly trades and cross equatorial flow into the Northern Hemisphere and (ii) weakening of westerly flow over the North Indian Ocean. Similarly, in the upper level flow (200 hPa) they indicate (i) weakening of Tibetan anti-cyclone and (ii) reduction of return flow into the Southern Hemisphere. The balance requirements in the mean analysis as well as forecast fields are fairly in agreement with the observed over the summer monsoon. The monsoon domain is discerned as the source region of kinetic energy and vorticity. Both are produced in the monsoon region and transported horizontally across. The model forecasts fail to retain the analyzed atmospheric variability in terms of mean as well as transient circulations which is revealed by kinetic energy budget. This is further corroborated by vorticity and angular momentum budgets. It is noticed that the forecasts in all ranges produce feeble monsoon circulation which weakens considerably with increase in the forecast period.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01025385
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