Constraining near-surface water vapor on Mars: a spectral synergy climatological survey applied to PFS and SPICAM nadir observations
Elise W. Knutsen1, Franck Montmessin1, Loic Verdier1, Gaétan Lacombe1, Franck Lefèvre1, Stéphane Ferron2, Marco Giuranna3, Paulina Wolkenberg3, Anna Fedorova4, Alexander Trokhimovskiy4, Oleg Korablev4
1LATMOS/IPSL, UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, Guyancourt, France
2ACRI-ST, boulevard des Garennes, Guyancourt, France
3IAPS-INAF, Rome, Italy
4Space Research Institute (IKI), Moscow, Russia
Corresponding author: Elise Wright Knutsen (elise-wright.knutsen@latmos.ipsl.fr)
Key Points:
Abstract
With the utilization of a novel synergistic approach, we constrain the vertical distribution of water vapor on Mars with measurements from nadir-pointing instruments. Water vapor column abundances were retrieved simultaneously with PFS (sensing the thermal infrared range) and SPICAM (sensing the near-infrared range) on Mars Express, yielding distinct yet complementary sensitivity to different parts of the atmospheric column. We show that by exploiting a spectral synergy retrieval approach, we obtain more accurate water vapor column abundances compared to when only one instrument is used, providing a new and highly robust reference climatology from Mars Express. We present a composite global dataset covering all seasons and latitudes, assembled from co-located observations sampled from seven Martian years. The synergy also offers a way to study the vertical partitioning of water, which has remained out of the scope of nadir observations made by single instruments covering a single spectral interval. Special attention is given to the north polar region, with extra focus on the sublimation of the seasonal polar cap during the late spring and summer seasons. Column abundances from the Mars Climate Database were found to be significantly higher than synergistically retrieved values, especially in the summer Northern Hemisphere. Deviances between synergy and model in both magnitude and meridional variation of the vertical confinement were also discovered, suggesting that certain aspects of the transport and dynamics of water vapor are not fully captured by current models.