TOTAL COLUMN WATER VAPOUR RETRIEVAL OVER NAIROBI USING THE MAX-DIFFERENTIAL OPTICAL ABSORPTION SPECTROMETER (MAX-DOAS) AND VALIDATION WITH SATELLITE DATA

Abstract

The installation of a MAX-DOAS instrument at UNEP headquarters, Gigiri by Bremen University in March 2002 was seen as a possible aid to more accurate weather prediction tools. The purpose of our study was to retrieve water vapour amount in the Nairobi atmosphere using the Gigiri instrument and the validation of these measurements using the water vapour amount obtained through SCIAMACHY, a MAX-DOAS instrument on board the ENVISAT satellite. Validation ensures that the accuracy of the measurements is maintained.We have in this study obtained water vapour slant columns as well as the vertical columns above Nairobi. Vertical column water vapour above Nairobi reaches a maximum value of 5g/cm2 during the rainy seasons of March-April and November-December and drops to a minimum of 2.5g/cm2 in the dry months of June-July and January-February. The values obtained through the Nairobi instrument agree well with the values obtained satellite measurement. Both instruments indicate that atmospheric water vapour amount over Nairobi fluctuates between highs of about 5g/cm2and lows of about 3g/cm2 but has a high tendency to settle at around 4g/cm2.