Mars water vapor abundance from SPICAM IR spectrometer: Seasonal and geographic distributions

Abstract

The near‐IR channel of SPICAM experiment on Mars Express spacecraft is a 800‐g acousto‐optic tunable filter (AOTF)–based spectrometer operating in the spectral range of 1–1.7 μm with resolving power of ∼2000. It was put aboard as an auxiliary channel dedicated to nadir H 2 O measurements in the 1.37‐μm spectral band. This primary scientific goal of the experiment is achieved though successful water vapor retrievals, resulting in spatial and seasonal distributions of H 2 O. We present the results of H 2 O retrieval from January 2004 (L s = 330°) to December 2005 (L s = 340°), covering the entire Martian year. The seasonal trend of water vapor obtained by SPICAM IR is consistent with TES results and reveals disagreement with MAWD results related to south pole maximum. The main feature of SPICAM measurements is globally smaller water vapor abundance for all seasons and locations including polar regions, as compared to other data. The maximum abundance is 50–55 precipitable microns at the north pole and 13–16 precipitable microns (pr μm) at the south pole. The northern tropical maximum amounts to 12–15 pr μm. Possible reasons for the disagreements are discussed.