Analysis of heat flux by RASS and comparison with airplane measurements

Abstract

On June 28, 1996, RASS (radio-acoustic sounding system) and aircraft observations were taken of the evolving boundary layer as part of the Montreal experiment on regional mixing and ozone (MERMOZ). The vertical air velocity measurements of the RASS were exceptionally free of clutter or interference. The RASS observation period spans from 1045 to 1400 EST. The aircraft observations were taken between 1155 and 1335 EST, along 35 km long east-west runs, at a distance of 30 km north-east of the RASS site. Time-height plots of the RASS clear-air signal-to-noise ratio, virtual potential temperature, and vertical air velocity reveal a boundary layer that is very convective. The inversion height starts at 600 m AGL and grows to about 1 km AGL, and well defined vertical structures of rising and sinking air are evident. Derived quantities from RASS data indude virtual temperature fluctuations, heat flux traces, and heat flux quadrants. Corresponding time-height plots are consistent with the descriptions of a convective boundary layer given by Schmidt and Schumann (1989), among others. The convective boundary layer is seen to be very nonstationary. Heat flux profiles of RASS and aircraft data are comparable up to 500 m AGL, but heat flux cospectra of RASS and aircraft data are shown to have different forms.

Keywords

• radio-acoustic sounding system
• aircraft observations
• montreal experiment on regional mixing and ozone (mermoz)
• boundary layer
• radio-akustisches sonierungs-system
• grenzschicht