• M D Chipade

      Articles written in Journal of Earth System Science

    • Upper and lower tropospheric energetics of standing and transient eddies in wave number domain during summer monsoon of 1991

      S M Bawiskar M D Chipade D K Paul S S Singh

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      Kinetic energy exchange equations (Saltzman 1957) in wave number domain are partitioned into standing, transient and standing-transient components following Murakami (1978, 1981). These components are computed for the 1991 summer monsoon using dailyu andv grid point data at 2.5° latitude-longitude interval between the equator and 40°N at 200 hPa and 850 hPa levels for the period June through August. The data are obtained from NCMRWF, New Delhi.

      The study shows that at 200 hPa wave number 1 over Region 3 (30°N to 40°N), wave number 2 over Region 2 (15°N to 30°N) and wave number 3 over Region 1 (equator to 15°N) dominate the spectrum of transport of momentum and wave to zonal mean flow interaction. Wave number 1 over Region 1 and Region 3 and wave number 2 over Region 2 are the major sources of kinetic energy to other waves via wave-to-wave interaction. At 850 hPa wave number 1 over Region 3 has maximum contribution in the spectrum of transport of momentum and kinetic energy and more than 90% of its contribution is from the standing component. This indicates that standing wave number 1 over Region 3 plays a very important role in the dynamics of monsoon circulation of the lower troposphere.

      The study further shows that although the circulation patterns at 200 hPa and 850 hPa levels are opposite in character, a number of energy processes exhibit a similar character at these levels. For example, (i) transport of momentum by most of the waves is northward, (ii) small scale eddies intensify northward, (iii) eddies are sources of kinetic energy to zonal mean flow over Region 1 and (iv) standing eddies are sources of kinetic energy to transient eddies. Besides the above similarities some contrasting energy processes are also observed. Over Region 2 and Region 3 standing and transient eddies are sources of kinetic energy to zonal mean flow at 200 hPa, while at 850 hPa the direction of exchange of kinetic energy is opposite i.e. zonal mean flow is a source of kinetic energy to standing as well as transient eddies. L(n) interaction indicates that at 200 hPa waves over R2 maintain waves over R1, while at 850 hPa waves over R1 maintain waves over R2.

      It has been found that the north-south gradient of zonal mean of zonal wind is the deciding factor of wave to zonal mean flow interaction.

    • Intra-seasonal variations of kinetic energy of lower tropospheric zonal waves during northern summer monsoon

      S M Bawiskar M D Chipade S S Singh

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      Space spectral analysis of zonal (u) and meridional (v) components of wind and time spectral analysis of kinetic energy of zonal waves at 850 hPa during monsoon 1991 (1st June 1991 to 31st August 1991) for the global belt between equator and 40°N are investigated. Space spectral analysis shows that long waves (wavenumbers 1 and 2) dominate the energetics of Region 1 (equator to 20°N) while over Region 2 (20°N to 40°N) the kinetic energy of short waves (wavenumbers 3 to 10) is more than kinetic energy of long waves. It has been found that kinetic energy of long waves is dominated by zonal component while both (zonal and meridional) the components of wind have almost equal contribution in the kinetic energy of short waves.

      Temporal variations of kinetic energy of wavenumber 2 over Region 1 and Region 2 are almost identical. The correlation matrix of different time series shows that (i) wavenumber 2 over Regions 1 and 2 might have the same energy source and (ii) there is a possibility of an exchange of kinetic energy between wavenumber 1 over Region 1 and short waves over Region 2. Wave to wave interactions indicate that short waves over Region 2 are the common source of kinetic energy to wavenumber 2 over Regions 1 and 2 and wavenumber 1 over Region 1. Time spectral analysis of kinetic energy of zonal waves indicates that wavenumber 1 is dominated by 30–45 day and bi-weekly oscillations while short waves are dominated by weekly and bi-weekly oscillations.

      The correlation matrix, wave to wave interaction and time spectral analysis together suggest that short period oscillations of kinetic energy of wavenumber 1 might be one of the factors causing dominant weekly (5–9 day) and bi-weekly (10–18 day) oscillations in the kinetic energy of short waves.

    • Energetics of lower tropospheric planetary waves over mid latitudes: Precursor for Indian summer monsoon

      S M Bawiskar M D Chipade P V Puranik U V Bhide

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      Based on NCEP/NCAR reanalysis data, kinetic energy and momentum transport of waves 0 to 10 at 850 hPa level are computed from monthly mean zonal (u) and meridional (v) components of wind from equator to 90‡N. Fourier technique is used to resolve the wind field into a spectrum of waves. Correlation analysis between All India Seasonal Monsoon Rainfall (AISMR) and energetics of the waves indicates that effective kinetic energy of waves 1, 3 and 4 around 37.5‡N in February has significant correlation (99.9%) with the subsequent AISMR. A simple linear regression equation between the effective kinetic energy of these three waves and AISMR is developed. Out of 47 years’ (1958–2004) data, 32 years (1958–1989) are utilized for developing the regression model and the remaining 15 years (1990–2004) are considered for its verification. Predicted AISMR is in close agreement with observed AISMR. The regression equation based on the dynamics of the planetary waves is thus useful for Long Range Forecasting (LRF) of AISMR. Apart from the regression equation, the study provides qualitative predictors. The scatter diagram between AISMR and effective kinetic energy of waves 1, 3 and 4 around 37.5?N indicates that if the kinetic energy is more (less) than 5m2s-2, the subsequent monsoon will be good (weak). Stream function fields indicate that high latitude trough axis along 40‡E (70‡E) leads to a good (weak) monsoon over India.

    • Energetics of lower tropospheric ultra-long waves: A key to intra-seasonal variability of Indian monsoon

      S M Bawiskar M D Chipade P V Puranik

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      Analysis of fifty four (1951-2004)years of daily energetics of zonal waves derived from NCEP/ NCAR wind (𝑢 and 𝑣 data and daily rainfall received over the Indian landmass (real time data) during southwest monsoon season (1 June-30 September)indicate that energetics (momentum transport and kinetic energy)of lower tropospheric ultra-long waves (waves 1 and 2)of low latitudes hold a key to intra-seasonal variability of monsoon rainfall over India.

      Correlation coefficient between climatology of daily (122 days)energetics of ultra-long waves and climatology of daily rainfall over Indian landmass is 0.9.The relation is not only significant but also has a predictive potential.The normalised plot of both the series clearly indicates that the response period of rainfall to the energetics is of 5-10 days during the onset phase and 4-7 days during the withdrawal phase of monsoon over India.During the established phase of monsoon, both the series move hand-in-hand.Normalised plot of energetics of ultra-long waves and rainfall for individual year do not show marked deviation with respect to climatology.These results are first of its kind and are useful for the short range forecast of rainfall over India.

    • Impact of global warming on the energetics of lower tropospheric ultra-long waves and the Indian summer monsoon

      M D Chipade J R Kulkarni S M Bawiskar

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      Analyses of 60 years (1949–2008) of monthly energetics of the zonal waves derived from NCEP/NCAR data indicate that ultra-long waves (waves 1 and 2) dominate the spectrum of lower tropospheric zonal waves during monsoon season (June–September). Westerlies over the Indian subcontinent are a source of energy to wave 1. Two oceanic anticyclones, one over Pacific and the other over Atlantic are sources of energy to wave 2. These two waves are inversely correlated. Climatology of the energetics of ultralong waves for the two epochs 1949–1978 (CLP1) and 1979–2008 (CLP2) of 30 years indicates that the intensity of wave 1 has decreased by about 33% whereas the intensity of wave 2 has increased by about 27%. Northward transport of sensible heat during CLP1 changes to southward during CLP2. Larger generation of zonal mean Available Potential Energy (APE) during CLP2 indicates more heating. A larger conversion of kinetic energy (KE) of wave 1 into APE of wave 1 leads to weakening of wave 1 during CLP2. In case of wave 2, lower rate of conversion of KE to APE leads to stronger wave 2 during CLP2. slagging and heating values of the coal has been found in this study.

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