Modeling the diurnal tide with dissipation derived from UARS/HRDI measurements

International audienceThis paper uses dissipation values derived from UARS/HRDI observations in a recently published diurnal-tide model. These model structures compare quite well with the UARS/HRDI observations with respect to the annual variation of the diurnal tidal amplitudes and the size of the amplitudes themselves. It is suggested that the annual variation of atmospheric dissipation in the mesosphere-lower thermosphere is a major controlling factor in determining the annual variation of the diurnal tide

Ultrathin Tropical Tropopause Clouds (UTTCs) : I. Cloud morphology and occurrence

Subvisible cirrus clouds (SVCs) may contribute to dehydration close to the tropical tropopause. The higher and colder SVCs and the larger their ice crystals, the more likely they represent the last efficient point of contact of the gas phase with the ice phase and, hence, the last dehydrating step, before the air enters the stratosphere. The first simultaneous in situ and remote sensing measurements of SVCs were taken during the APE-THESEO campaign in the western Indian ocean in February/March 1999. The observed clouds, termed Ultrathin Tropical Tropopause Clouds (UTTCs), belong to the geometrically and optically thinnest large-scale clouds in the Earth´s atmosphere. Individual UTTCs may exist for many hours as an only 200--300 m thick cloud layer just a few hundred meters below the tropical cold point tropopause, covering up to 105 km2. With temperatures as low as 181 K these clouds are prime representatives for defining the water mixing ratio of air entering the lower stratosphere

Modeling the diurnal tide with dissipation derived from UARS/HRDI measurements

This paper uses dissipation values derived from UARS/HRDI observations in a recently published diurnal-tide model. These model structures compare quite well with the UARS/HRDI observations with respect to the annual variation of the diurnal tidal amplitudes and the size of the amplitudes themselves. It is suggested that the annual variation of atmospheric dissipation in the mesosphere-lower thermosphere is a major controlling factor in determining the annual variation of the diurnal tide

Diurnal migrating tide as seen by high-resolution Doppler imager/UARS: 1. Monthly mean global meridional winds

The high-resolution Doppler imager (HRDI) instrument on board the upper atmosphere research satellite measures global winds in the mesosphere and lower thermosphere on a day-to-day basis. The horizontal coverage of the HRDI data is excellent and provides a unique opportunity to study global-scale dynamic phenomena; however, the local time resolution and coverage are limited because of the nature of the satellite sampling. The lack of local time coverage makes conventional methods of data analysis (e.g., Fourier analysis) both difficult and erroneous. An original method of analysis, based on a numerical model of atmospheric thermal tides, is proposed and applied to the HRDI data. The tidal model is solved for the tidal oscillations in the meridional wind component. The simulated diurnal meridional tidal winds are used as a first guess in the analysis. The results of the model are adjusted to give meridional migrating tidal winds that have maximum consistency with HRDI measurements. This technique is used to derive monthly mean tidal oscillations of the meridional velocity. The derived tidal amplitudes show profound seasonal changes that seem to be consistent with gravity wave breaking theory. The results are compared with MF radar data. It is found that in the upper mesosphere and lower thermosphere, the tidal amplitudes obtained by HRDI can be bigger than those from MF radars by a factor of 2.Khattatov, BV; Yubin, VA; Geller, MA; Hays, PB; Vincent, R

Modeling the diurnal tide with dissipation derived from UARS/ HRDI Measurements. Ann. Geophysicae, this issue

Abstract. This paper uses dissipation values derived from UARS/HRDI observations in a recently published diurnal-tide model. These model structures compare quite well with the UARS/HRDI observations with respect to the annual variation of the diurnal tidal amplitudes and the size of the amplitudes themselves. It is suggested that the annual variation of atmospheric dissipation in the mesosphere-lower thermosphere is a major controlling factor in determining the annual variation of the diurnal tide.