Understanding Boundary Layer in Desert Climates

  • Mohamed Abdul Majeed Al Marzooqi

Student thesis: Master's Thesis

Abstract

Strong sensible heat fluxes and deep turbulent mixing together with marked dustiness and a low substrate water content represent a characteristic signature of the atmospheric boundary layer over hot deserts, resulting in thicker mixing layers and peculiar optical properties. Beside these main common features however, desert boundary layers present extremely complex local structures that have been scarcely addressed in the literature, and whose understanding is essential in modeling processes such as the transport of dust and pollutants, local wind fields and turbulent fluxes of momentum, heat and water vapor. In this study, we analyze a continuous record of observations of the atmospheric boundary layer from a single lens LiDAR ceilometer operated at Masdar Institute Field Station starting March 2013. The main objective is to shade some light on the structure and dynamics of atmospheric boundary layer in hyper-arid regions. At this goal, we compare the performance of different methods for the estimation of boundary layer top from Ceilometer data such as classic gradient-, second derivation-, log gradient-, variance-, and wavelets-methods with a bi-dimensional technique we developed as a modification of the recently proposed single-profile clustering method. Our assumption is that the probability distribution of each range corrected back-scattering profile obtained from the ceilometer is a convolution of diverse normal probability density distributions each one representing the concentration, size and shape of the tracers in the considered layer, and that a de-convolution of the signal also via a simple clustering technique should be sufficient to identify the different layers in the profile. We show that the here proposed bi-dimensional clustering method represents a very promising tool for understanding the complex layering of atmospheric boundary layer in hot sandy deserts.
Date of AwardMay 2014
Original languageAmerican English
SupervisorAnnalisa Molini (Supervisor)

Keywords

  • Atmospheric Boundary Layer; Desert Climates; Heat Flux; Potential Temperature.

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