FöRFATTARE
Johansson, Erik

INSTITUTION
Rymdvetenskap, Kiruna /

SAMMANFATTNING
The purpose of this master's thesis is to investigate the daily cycle of Upper Tropospheric Humidity (UTH). The used data come from the satellites NOAA--15 - 18 and MetOp--A that are carrying the microwave instruments AMSU--B or MHS. AMSU--B and MHS measure the thermal radiance emitted from the earth's surface and atmosphere. These data have then been recalculated to Upper Tropospheric Humidity and Deep Convective Clouds (DCC). The data that were used come from the time period December 2006 -- November 2007 and were divided into four periods that correspond to four seasons.

The data used come with time stamps in Universal Time (UT), so firstly it had to be recalculated to Local Solar Time (LST). During these calculations it was found that at one point NOAA--15 and NOAA--16 were flying very close to each other. To test the inter calibration between the two satellites, their data from this time period were compared. The nature of the difference lead to the conclusion that the data from the NOAA--15 satellite were not reliable due to limb effect and therefore the data from this satellite were discarded from the rest of the thesis.

To the measurements a cosine function was fitted to determine the diurnal cycle. Both UTH and DCC were found to have their largest diurnal amplitude over land close to the equator. These areas are the same as the areas with highest UTH value. The time when the maxima occur was in the night over both land and oceans for the UTH while for DCC it varies from early evening over land to morning over ocean. This seems to be in correlation with the earlier studies of UTH and DCC even though small differences were found. The areas with high UTH follow the local summer. Therefore, there were some small differences in areas with a diurnal cycle far from the equator due to season. The maximum of the daily cycle was not affected by the seasons. The Ice Water Path (IWP) was also investigated. It was found that its diurnal cycle follows the DCC cycle.

ISSN 1653-0187 / ISRN LTU-PB-EX--09/028--SE / NR 2009:028