Spectral estimation of Type I cloud-topped boundary layers

James Vincent Aanstoos, Purdue University

Abstract

A technique has been developed and tested for extracting structural features of boundary layer thermal convection from meteorological satellite imagery. Data from satellite-borne imaging radiometers as well as aircraft-based instruments have been used to investigate the spatial structure of the organized mesoscale cloud fields associated with Type I convective marine boundary layers. The method, based on Fourier analysis, has been tested in the context of an investigation of the solar radiation data from Cold Air Outbreaks (CAOs) in two meteorological field studies, Project LESS and GALE. In both cases, ambient measurements of downward solar radiation made from aircraft in or below the cloud layer were analyzed using rigorous spectral estimation techniques designed to detect significant spectral features in the face of limitations such as marginal data set resolution and record length. A fundamental question answered was whether or not (or to what extent) the length scales present in the spectra of the remotely sensed image data are similar to those manifested in the spectra of locally measured meteorological variables such as temperature, moisture, and velocity fields which are more directly related to the underlying turbulent flow. The results obtained in this investigation show that at least one of the two significant spectral features identified with Type I CTBLs--the Higher Convective Mode (HCM) length scale--can be detected with moderate statistical confidence in GOES satellite imagery and the shorter-wavelength Basic Convective Mode (BCM) spectral peak can be detected with even greater confidence in higher-resolution Landsat imagery during GALE. Both modes were also detected with confidence in the LESS aircraft radiation data, while in the GALE case only the BCM was detected due to the shorter record length.

Degree

Ph.D.

Advisors

Agee, Purdue University.

Subject Area

Atmosphere

COinS