Use of satellite data for radiative energy budget study of Indian summer monsoon

In this paper satellite-derived radiative energy budget such as shortwave radiative heating, longwave radiative heating and net radiation balance have been studied for the post-onset phase of summer monsoon 1979. Since clouds play an important role in determining diabatic heating field as well as being a reflection of status of the monsoon itself, the day to day evolution of clouds from TIROS-N satellite has been made. Satellite-derived radiative heating rates from surface to 100 hPa were computed for each 100 hPa thickness layer. These heating rates were then compared with the observed latitudinal distribution of total radiative heating rates over the domain of the study. From the results of our study it was found that the characteristic features such as net radiative heating rates of the order of 0.2°C/day at upper tropospheric layer (100-200 hPa) and cooling throughout the lower tropospheric layers with relatively less cooling between 500-700 hPa layer observed in a case of satellite-derived radiative energy budget agree well with the characteristic features of observational radiative energy budget over the domain of the study. Therefore, it is suggested that radiative energy budget derived from satellite observations can be used with great potential and confidence for the evolution of the complete life cycle of the monsoon over the Indian region for different years

Satellite observed wind forcing over the southwest equatorial Indian ocean during Indian summermonsoon

In this paper, satellite-observed wind forcing in the form of strong surge of cold air through Mozambique channel and along east African coast, under the influence of eastward propagating baroclinic wave disturbances over southwest Indian ocean has been studied during various summer monsoon seasons. Further, its impact on the intensification of monsoon systems over the Arabian sea through the excitation of low-level jet and associated cross-equatorial flow has been illustrated. For this purpose, satellite-observed cloud imagery, obtained from TIROS-N, NOAA, DMSP, GOES and INSAT satellites during 1979 and 1988-95,have been utilized for finding latitudinal positions of the cold fronts across south African-Malgassy region (i.e. 30°S, I -40°E), GOES(IO) and INSAT derived low level cloud drift winds in the domain 2.5°S to 2.5°N and 40°50°E have been used to observe the triggering of low level jet and associated cross equatorial flow. Daily rainfall of ten stations viz. Tiruvananthapuram, Alleppy, Cochin, Kozikhode, Mangalore, Karwar, Goa, Ratnagiri, Bombay and Dahanu have been used for finding the modulation of the rainfall activity along the west coast of India. From the results of the study it is inferred that there is an abrupt increase in the strength of low-level wind flow along east African coast 2 to 3 days after the first appearence of northward propagating cold front across south African-Malgassy region. This is followed by intensification of the rainbearing monsoon systems (e.g. ITCZ, lows, off shore troughs etc.) over the Arabian sea giving increase in rainfall activity along the west coast of India. Therefore it is suggested that above association between northward-propagating cold front across south African-Malgassy region and excitation of low-level cross-equatorial flow can be linked to forecast increase in rainfall activity alone the west coast of India 5-7 days in advance

Response of the Bay of Bengal to Gopalpur and Paradip super cyclones during 15-31 October 1999

Response of the Bay of Bengal to two tropical cyclones, i.e. Gopalpur and Paradip super cyclones, during 15-31 October 1999, is studied using a stationary mooring buoy for marine meteorological observations. The National Institute of Ocean Technology (NIOT, Chennai) has deployed this buoy at 13°N, 87°E, by fixing various meteorological instruments and sensors to acquire sea surface temperature (SST), air temperature (Ta), wind speed (Ws), wind direction (Wd) and ocean currents (Cs) using remote sensing technique through INSAT-1D satellite at an interval of 3 h. The results of the analysis of the above parameters have shown clearly a response (SST difference between before and after formation) of about 0.7°C for the Gopalpur cyclone and 0.9°C for the Paradip cyclone. Ta has shown rapid variations following the rapid movement of cloud decks across the buoy during the cyclone period. The observed changes in the wind speed and direction are in concurrence with analysed mean sea level pressure oscillations. Finally, this study recommends more buoy-based marine meteorological observations over this region and the neighbouring areas, where the tropical cyclones generally occur and subsequently hit the Coromandal coast

Influence of wind speed on surface layer stability and turbulent fluxes over southern Indian peninsula station

Surface to atmosphere exchange has received much attention in numerical weather prediction models. This exchange is defined by turbulent parameters such as frictional velocity, drag coefficient and heat fluxes, which have to be derived experimentally from high-frequency observations. High-frequency measurements of wind speed, air temperature and water vapour mixing ratio (eddy covariance measurements), were made during the Integrated Ground Observation Campaign (IGOC) of Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) at Mahabubnagar, India (16∘44′N, 77∘59′E) in the south-west monsoon season. Using these observations, an attempt was made to investigate the behaviour of the turbulent parameters, mentioned above, with respect to wind speed. We found that the surface layer stability derived from the Monin–Obukhov length scale, is well depicted by the magnitude of wind speed, i.e., the atmospheric boundary layer was under unstable regime for wind speeds >4 m s−1; under stable regime for wind speeds <2 m s−1 and under neutral regime for wind speeds in the range of 2–3 m s−1. All the three stability regimes were mixed for wind speeds 3–4 m s−1. The drag coefficient shows scatter variation with wind speed in stable as well as unstable conditions

Variability of lightning, convective rain and solar activity study over South/Southeast Asia during ENSO episode for the period of 1998-2010

Abstract Analysis of monthly mean data of lightning and convective rain for the region 8° N - 35° N, 60° E - 120° E and for the period 1998-2010 show that lightning and convective rain are not significantly influenced by solar parameters such as sunspot number, total solar irradiance (TSI) and solar radio flux whereas CAPE anomaly and temperature anomaly have significant impact on the total lightning flash rate and convective rain during ENSO periods. Further no significant relation between cosmic ray flux and total lightning flash rate during La Niña period is obtained. On the other hand, for the El Niño period and for the total period, we get statistically some significant negative correlation between cosmic ray flux and total lightning flash rate. However, it is not possible to make any comment on the general relation between cosmic ray flux and total lightning flash rate due to contaminating global effects, regional effects and cloud microphysics. In the monthly variation of the parameters, temperature anomaly can be used as a proxy for the total lightning flash rate for the region under consideration. Most of the variation in ozone during the ENSO period is due to lightning. In the region considered here, role of aerosols in producing lightning and rainfall is quite comparable during La Niña period. On the other hand, aerosols contribute more towards production of lightning than producing rain during El Niño due to changes in cloud microphysics and cloud electrification

Oscillation of wind temperature humidity in the atmospheric surface layer over tropical semi-arid stations

Analysis of wind, air temperature, humidity and rainfall data from Land Surface Processes Experiment (LASPEX) in the surface layer at Anand (22°35′N, 72°55′E) and Khandha (22°02′N, 73°11′E) during January to December 1997 is presented. Wind and temperature at various levels showed prominent diurnal variation. Progression of daily wind and temperature revealed the intra-seasonal, quasi-biweekly and 6–9 day oscillations indicated large-scale convection, transport of heat and water vapor from Arabian Sea towards these stations.Power spectrum of wind and humidity corroborated the planetary scale Madden–Julian oscillation in the surface layer. Periodic oscillations of 21, 6–9, 1 day and 12 h were prominent in the spectrum of all variables. Low-frequency spectral peaks showed the energy in wind is 2–3 times higher over Khandha than at Anand whereas temperature is 3 times higher at Anand than Khandha

Turbulence characteristics in the atmospheric surface layer during summer monsoon of 1997 over a semi-arid location in India

A land surface processes experiment (LASPEX) was conducted in the semi-arid region of Northwest India during January 1997–February 1998. Analysis of turbulent components of wind and air temperature collected in the surface layer (SL) at Anand (22°35′N, 72°55′E) during the Indian summer monsoon season from June to September 1997 is presented. Turbulent fluctuation of wind components and air temperature observed at Anand varied as a function of terrain features and stability of the surface layer. Under neutral conditions, the standard deviation of vertical velocity (σ w ) and temperature (σ T ) were normalized using respective surface layer scaling parameter u * and T * which fitted the expressions σ w /u * = 1.25 and σ T /T * ≈ 4. Micrometeorological spectrum of wind and temperature at 5 m above ground level (AGL) at Anand showed peaks at time scale of 1–3 min at the low-frequency end. The inertial sub-range characteristics (−2/3 slope) of the spectrum are exhibited mostly. However, in some occasions, slope of −1 denoting brown noise was depicted by the wind and temperature spectrum, which indicated anisotropy in turbulenc

Salient features of Andhra Pradesh cyclonic storm in the Bay of Bengal during September 1997

During 23-30 September 1997, a rare cyclonic storm has developed close to the Andhra coast, and it has later travelled parallel to coastline northward and finally crossed the land at Chittagong (22°N, 91°E) on 27 September. While translating along the east coast of India, it has produced heavy to very heavy rainfall on the coastal stations causing devastating floods. In this study, we made an attempt to understand the salient causes of this unique cyclone movement. We have analyzed daily fields of wind and relative humidity for 850, 700, 500 hPa and mean daily OLR data to understand the plausible reasons for its movement. The buoy data deployed by National Institute of Ocean Technology, Chennai, Viz. DS5 (15°N, 81°E), DS4 (19°N, 88°E) and SW7 (20°N, 86°E) were analyzed to understand the ocean-atmosphere interaction processes in the west Bay of Bengal during formation of the system. Analysis of OLR over the cyclonic storm region has revealed that the heavy rainfall areas coincide with low OLR (120-180 W m -2). The persistent southward movement of 500 hPa ridge on the eastern wedge of the system along with the steering current at 200 hPa has helped in maintaining the movement of the system parallel to the east coast of India during its life cycle

Cloud aerosol interactions and its influence on cloud microphysical parameters during dry and wet spells of Indian summer monsoon using CAIPEEX data

The variations of cloud condensation nuclei (CCN), aerosol and cloud particle concentration (PCASP), cloud droplet effective radius (CDPRe), and Liquid water content (LWC) have been measured using instrumented aircraft over Hyderabad, Bengaluru and Bareilly in India during Cloud Aerosol Interactions and Precipitation Enhancement Experiment (CAIPEEX-2009). Three intensive observation periods (IOPs) i.e. 17-22 June and 13 July representing the dry spells, and the IOP during 16-25 August, representing wet spells of Indian summer monsoon were analyzed. Cloud droplet size is highly sensitive to liquid water content and temperature in the cloud environment. The CDPRe and LWC show strong linear correlation during both dry spells and wet spells of ISMR. The mid level clouds CM ~ 2000 meters are more favorable for coalescence of cloud droplets leading to growth of CDPRe > 14 µm required for warm rain formation