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:
- Using a spectral synergy retrieval method on nadir observations from
SPICAM and PFS to obtain a highly accurate water vapor climatology.
- The synergy method is sensitive to the vertical distribution of
H2O, and can distinguish near-surface water from the
rest of the column.
- Discrepancies in meridional and seasonal behavior of vertical
confinement are revealed between the synergy and the Mars Climate
Database.
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.