COMPARISON OF GEOMORPHICALLY DETERMINED WINDS WITH A GENERAL CIRCULATION MODEL: HERSCHEL CRATER, MARS C. T. Adcock

Introduction: Wind is the dominate geologic process currently at work on the surface of Mars [1]. An understanding of surface winds is paramount if we are to understand Mars as a planet. Further, winds and the entrained particles within them can have a detrimental impact on equipment, structures, and future missions [2]. The Russian probe Mars 3, for example, is thought to have been rendered inoperative by winds it encountered during landing [3]. General circulation models (GCM) have been created for surface winds of Mars [4, 5]. These GCM are powerful tools for describing and understanding surface winds of a planet. However, the GCM for Mars have not been thoroughly validated due to a lack of ground truth data. Interpretation and correlation of wind regimes from geomorphic analogy may be useful for validating GCM in the absence of ground truth data. Studies on the relationship between wind and landforms observed on Earth are plentiful [6-9]. Bagnold’s 1941 book, The Physics of Blown Sand and Desert Dunes, details not only dune types but the types of winds, materials and material supplies required to create them. Authors such as Lancaster [10] have updated and refined Bagnold’s work and today eolian landforms, especially dunes and the winds required to generate them, are reasonably well characterized for Earth. These studies have benefited from extensive field work and later the aid of remote sensing. Through geomorphic analogy, the knowledge gained from terrestrial studies can be applied to Mars. Though ground truth data for Mars is limited, remotely sensed data from flyby and orbiter missions is extensive. Our current Martian image catalog consists of data from nearly a dozen successful orbiter missions with spatial resolutions as high as 1.4 meters per pixel. In a previous study by the authors [11], these remotely sensed data in combination with geomorphic terrestrial analogy have been used to infer wind directions in Herschel Crater. In this study we compare the results of the inferred determinations to a general circulation model (GCM) of surface winds for the area. Herschel Crater: Herschel Crater is a 300 km diameter impact crater located in the southern highlands of Mars northeast of Hellas Basin and in the eastern part of Mare Tyrrhenum. It is centered at approximately 228° W longitude and 15° S latitude (Figure 1). The area was chosen after a preliminary search of data revealed that some of the remote sensed imagery for the location contained eolian features suitable for inferring wind direction. Figure 2 is an example of one such image.