Conserved variable analysis of the marine boundary layer and air-sea exchange processes using BOBMEX-Pilot data sets

The present study is based on the observed features of the MBL (Marine Boundary Layer) during the Bay of Bengal and Monsoon Experiment (BOBMEX) - Pilot phase. Conserved Variable Analysis (CVA) of the conserved variables such as potential temperature, virtual potential temperature, equivalent potential temperature, saturation equivalent potential temperature and specific humidity were carried out at every point of upper air observation obtained on board ORV Sagar Kanya. The values are estimated up to a maximum of 4 km to cover the boundary layer. The Marine Boundary Layer Height is estimated from the conserved thermodynamic profiles. During the disturbed period when the convective activity is observed, the deeper boundary layers show double mixing line structures. An attempt is also made to study the oceanic heat budget using empirical models. The estimated short-wave radiation flux compared well with the observations

Simulation of marine boundary layer characteristics using a 1-D PBL model over the Bay of Bengal during BOBMEX-99

The characteristic features of the marine boundary layer (MBL) over the Bay of Bengal during the southwest monsoon and the factors influencing it are investigated. The Bay of Bengal and Monsoon Experiment (BOBMEX) carried out during July-August 1999 is the first observational experiment under the Indian Climate Research Programme (ICRP). A very high-resolution data in the vertical was obtained during this experiment, which was used to study the MBL characteristics off the east coast of India in the north and south Bay of Bengal. Spells of active and suppressed convection over the Bay were observed, of which, three representative convective episodes were considered for the study. For this purpose a one-dimensional multi-level PBL model with a TKE-ε closure scheme was used. The soundings, viz., the vertical profiles of temperature, humidity, zonal and meridional component of wind, obtained onboard ORV Sagar Kanya and from coastal stations along the east coast are used for the study. The temporal evolution of turbulent kinetic energy, marine boundary layer height (MBLH), sensible and latent heat fluxes and drag coefficient of momentum are simulated for different epochs of monsoon and monsoon depressions during BOBMEX-99.The model also generates the vertical profiles of potential temperature, specific humidity, zonal and meridional wind. These simulated values compared reasonably well with the observations available from BOBMEX

Impact of land surface and forcing parameters on the spin-up behaviour of Noah land surface model over the Indian sub-continent

In the present study, an attempt is made to understand the influence of land surface parameters (such as soil moisture conditions, soil type and vegetation type) and forcing parameters on the model spin-up behaviour of a Land Surface Model (LSM), namely Noah LSM, over the Indian sub-continent. The work presented here primarily aims to understand the optimum initial conditions to achieve the least spin-up time over the subtropical conditions that exist over the region of interest. The study is presented in three major parts. In the first part, a multivariate statistical analysis, namely principle component analysis is employed to investigate how parameters such as precipitation, air temperature, soil moisture, radiation components as well as various parameters that characterize soil and vegetation types influence the model spin-up. The second part deals with the study of the impact of soil and vegetation parameters in different seasons on the model spin-up behaviour. Finally, the third part looks into the influence of initial soil moisture condition and precipitation forcing on the spin-up behaviour of the model in different seasons to obtain the optimum initial conditions for the minimum spin-up time of the model. From the study, it is seen that the soil and vegetation type, as well as the soil moisture content influence the model spin-up significantly. The present study reports that the experiments initialized just before a continuous rainfall event has the least spin-up unless the initial soil is saturated

A study on the structure of the convective atmosphere over the Bay of Bengal during BOBMEX-99

Convective activity is one of the major processes in the atmosphere influencing the local and large-scale weather in the tropics. The latent heat released by the cumulus cloud is known to drive monsoon circulation, which on the other hand supplies the moisture that maintains the cumulus clouds. An investigation is carried out on the convective structure of the atmosphere during active and suppressed periods of convection using data sets obtained from the Bay of Bengal and Monsoon Experiment (BOBMEX). The cumulus convection though being a small-scale phenomenon, still influences its embedding environment by interaction through various scales. This study shows the variation in the kinematic and convective parameters during the transition from suppressed to active periods of convection. Convergence in the lower levels and strong upward vertical velocity, significant during active convection are associated with the formation of monsoon depressions. The apparent heat source due to latent heat release and the vertical transport of the eddy heat by cumulus convection, and the apparent moisture sink due to net condensation and vertical divergence of the eddy transport of moisture, are estimated through residuals of the thermodynamic equation and examined in relation to monsoon activity during BOBMEX

Numerical simulation of the marine boundary layer characteristics over the Bay of Bengal as revealed by BOBMEX-98 Pilot experiment

An attempt has been made to study the marine boundary layer characteristics over Bay of Bengal using BOBMEX (Bay of Bengal and Monsoon Experiment) pilot experiment data sets, which was conducted between 23rd October and 12th November 1998 on board ORV Sagar Kanya. A one-dimensional multilevel atmospheric boundary layer with TKE-ε closure scheme is employed to study the marine boundary layer characteristics. In this study two synoptic situations are chosen: one represents an active convection case and the other a suppressed convection. In the present article the marine boundary layer characteristics such as temporal evolution of turbulent kinetic energy, height of the boundary layer and the airsea exchange processes such as sensible and latent heat fluxes, drag coefficient for momentum are simulated during both active and suppressed convection. Marine boundary layer height is estimated from the vertical profiles of potential temperature using the stability criterion. The model simulations are compared with the available observations

A study on air-sea exchange processes and conserved variable analysis over the Indian Ocean with INDOEX IFP-99 data

The exchange properties across the Marine Boundary Layer influence atmospheric convection and determine to a large extent the atmospheric circulation in the tropics. In view of these phenomena, an analysis of the surface parameters such as sea-surface temperature, air temperature, wind speed, moisture and cloud cover along the ORV Sagar Kanya and Ronald H. Brown cruise track was carried out. An attempt was made to examine the changes in these parameters while the ship was passing across the ITCZ region. The humidity was found to be considerably high over the ITCZ than non-ITCZ regions. The air-sea interaction processes were studied by computing the radiation fluxes (short-wave and longwave) and the turbulent heat fluxes (sensible heat and latent heat) using semi-empirical models. Over ITCZ region a net heat loss was found which can be attributed to large convergence, strong convective activity and dense cloud cover, leading to drastic reduction in short-wave radiation. Latitudinal and longitudinal variation of surface meteorological parameters and turbulent fluxes were studied to establish a link with the prevailing convective and clear weather regimes along the cruise tracks. A conserved variable analysis of the conserved variable such as potential temperature, virtual potential temperature, saturation equivalent potential temperature and specific humidity is carried out at every point of upper air observation from Ronald H. Brown. The values are estimated up to a maximum of 3 km to cover the boundary layer. In the ITCZ region due to the convective mixing deeper boundary layers are formed, where a double structure is observed. The Marine Boundary Layer Height is also estimated using thermodynamic profiles

An application of PIXE technique to Proto Crustal Rocks: Geo chemical evaluation of Granulitic Charnockites of Eastern Ghats, Andhrapradesh, India

In this work, PIXE has been used for a variety of Precambrian proto crustal rocks in the form of granulitic charnockites,Eastern Ghats AP,India.In previous study of exterior part of the charnockite hill elemental analysis using electron microprobe analysis, the elements in host charnockites no Na, traces of Mn,Ca and high Ti,Cl,F (Biotite), no Mn, low Na,and high K,Cl (Hastingsite), and Cl, Fe (Apatite) were only detected, but by using PIXE technique in addition to the above twenty two trace elements are identified. PIXE is highly sensitive and non-destructive method for multi elemental analysis in a variety of Precambrian charnockite rocks down to levels of a few parts per million. The samples chosen for analysis from the central portion of a charnockite hill near Visakhapatnam airport. A big reticular mass of relict litho logical body which is compositionally and physically different from host chatnockite was observed in the central portion of the hill. These experiments are carried out using a 3MV pelletron accelerator facility at the Institute of physics, Bhubaneswar. A collimated proton beam of 2mm diameter is made to fall on to the sample, and the beam current is kept at 20na. A high resolution Si(Li) detector(160ev FWHM at 5.9kev energy) is employed in the present experiments and the Guelph PIXE (GUPIX) software package is used to analyze the spectra. The elements identified in this Precambrian charnockite rock are Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Ru, Ag, Pb..From this study these rocks are early crust(proto crust) rocks. These samples are to belong to a very important geological phase and further work on petrography and REE (Rare Earth Elements in Geology)of the rock is indeed to firmly establish its exact parentage

Response of oceanic cyclogenesis metrics for NARGIS cyclone:a case study

In this study, variability of two oceanic cyclogenesis metrics, tropical cyclone heat potential (TCHP) and effective oceanic layer for cyclogenesis (EOLC) in the Bay of Bengal (BoB) during NARGIS cyclone is investigated. EOLC represents the geopotential thickness of near surface stratified layer forms because of the spread of low salinity waters due to fresh water influx from rivers and precipitation. Climatological fields of TCHP and EOLC reveal that NARGIS translated towards the region of higher EOLC as seen in the observations. A maximum daily sea surface cooling of 2 °C is observed along the right and rear side of NARGIS track

A comparative analysis of the characteristics of the Marine Boundary Layer with GCM and 1-D PBL model simulations using INDOEX IFP-99 data

Glass-sonde observations consisting of wind, temperature and relative humidity at different pressure levels that were obtained on board ORV Sagar Kanya cruise #141 (INDOEX IFP-99), during winter monsoon of 1999 were used for the present study. An attempt has been made to compare the simulation of the evolution of the Marine Boundary Layer as obtained from the one-dimensional PBL model of IIT Delhi, having TKE-ε closure scheme with that obtained from the GCM of NCMRWF having first order closure scheme. Simulation of various boundary layer characteristics including surface and upper air has been studied. The model simulations are compared with the available observations. Both the models simulated the vertical profiles reasonably well compared with the observations