The dissertation, I wrote from the results of scientific research during my tenure as a Scientific Research associate earned me my Ph.D. Degree in physics
Much of the research on ABL processes is mainly confined to studies over a horizontally homogeneous surface. But in real atmospheric conditions, such homogeneity and stationary seldom exist. Numerous investigations have been carried out to explore the micrometeorological processes where the boundary layer flow is influenced by the roughness change of the underlying terrain and temperature contrast between the surfaces, which induce local mesoscale circulations that ultimately influence the ABL processes. Thumba (8.5øN, 76.9øE), being an equatorial coastal station (at the Arabian seacoast), offers a site where the influence of the mesoscale processes to the ABL processes can be investigated. The investigations presented in this thesis cover, mainly, the experimental results of the study carried out at Thumba to provide insight into the ABL processes for a heterogeneous surface.
Chapter I gives a detailed description of the Atmospheric Boundary Layer (ABL) and a review of ABL studies carried out by other investigators.
Chapter II gives detailed description of the instruments used for the study of ABL namely a Doppler SODAR and a tower instrumented at three levels with sensors for insitu measurements temperature, humidity and 3-axis wind is dealt with.
Chapter III describes the general characteristics of the ABL at Thumba. This includes studies on mesoscale processes such as sea/land breeze circulations, nocturnal low-level jets, night time features and the formation of Thermal Internal Boundary Layers (TIBL).
Chapter IV deals with the turbulent characteristics of the coastal ABL over Thumba. The variances of wind components and temperature, fluxes of momentum and sensible heat and the surface layer stability parameter,-Z/L, have been computed using eddy correlation method. The day time variations of these parameters and their seasonal variability are discussed. The non-dimensional variances of the wind components are studied and their relationships with Z/L for different wind directions are presented. The variability of surface roughness, Zo with direction and the drag experienced by the wind with height when the flow crosses the line of discontinuity are examined. The observed profiles of wind speed are compared with the estimated profiles and the results are discussed taking into account the effect of local circulations on the wind profiles.
Chapter V deals with the spectral behaviour of ABL parameters such as three level wind components and temperature. Emphasis is given to the effects of mesoscale processes on the spectral behaviour of ABL parameters. Stability dependence of nocturnal spectra of wind fields is presented. Mesoscale spectrum of wind and their variations with season together with the effect of sea-breeze on the spectral gap is examined. Quantitative estimates such as the rate of dissipation of turbulent kinetic energy and their seasonal variations have been made.
Chapter VI deals with the study of sea-breeze fronts observed at Thumba as case studies. The characteristics of the frontal features as observed by SODAR and spectral study of vertical winds within the frontal zone are presented.
Chapter VII gives the summary of results, discussion and conclusion. The scope of future studies in this area also indicated.