Spatial and temporal distributions of Martian north polar cold spots before, during, and after the global dust storm of 2001

Abstract

[1] In the 1970s, Mariner and Viking observed features in the Mars northern polar region that were a few hundred kilometers in diameter with 20 mm brightness temperatures as low as 130 K (considerably below CO 2 ice sublimation temperatures). Over the past decade, studies have shown that these areas (commonly called ''cold spots'') are usually due to emissivity effects of frost deposits and occasionally to active CO 2 snowstorms. Three Mars years of Mars Global Surveyor Thermal Emission Spectrometer data were used to observe autumn and wintertime cold spot activity within the polar regions. Many cold spots formed on or near scarps of the perennial cap, probably induced by adiabatic cooling due to orographic lifting. These topographically associated cold spots were often smaller than those that were not associated with topography. We determined that initial grain sizes within the cold spots were on the order of a few millimeters, assuming the snow was uncontaminated by dust or water ice. On average, the half-life of the cold spots was 5 Julian days. The Mars global dust storm in 2001 significantly affected cold spot activity in the north polar region. Though overall perennial cap cold spot activity seemed unaffected, the distribution of cold spots did change by a decrease in the number of topographically associated cold spots and an increase in those not associated with topography. We propose that the global dust storm affected the processes that form cold spots and discuss how the global dust storm may have affected these processes.

Carbon dioxide snow clouds on Mars: South polar winter observations by the Mars Climate Sounder

“…It should be noted, however that smaller scale (and shorter‐lived) low emission regions are often observed under a sky that is clear down to ∼5 km altitude, although clouds may be present closer to the surface. Commonly associated with topography, these low emission regions may be generated by orographic snow clouds [cf Cornwall and Titus , 2009…”

“…Thus, T 12 – T 22 is diagnostic of CO 2 ice grain size or porosity [ Eluszkiewicz et al , 2005]. As a measurement of the depth of the transparency band of solid CO 2 , the T 12 – T 22 spectral contrast is similar to the “cold spot index” T 18 – T 25 used by Titus et al [2001] (also Cornwall and Titus [2009]) to identify low emission regions with the Thermal Emission Spectrometer (TES) onboard the Mars Global Surveyor.…”

“…Most of the spatial structures apparent inFigure 4 are regions of frequent low emission behavior throughout the study period, and we observe that many are at least qualitatively correlated with topographic slopes [cf. Cornwall and Titus , 2009, 2010]. Some regions known to exhibit high springtime albedo, notably the “Mountains of Mitchel” (320°W, 75°S) are also observed to have higher than average low‐emission activity.…”

“…Do small clouds also correlate with low nadir brightness temperatures? Their observed rapid formation and dissipation on time scales of hours or days [ Titus et al , 2001; Cornwall and Titus , 2009] makes direct correlation with nadir data difficult, since the probability of finding observations in the same spatial bin in both limb and nadir modes within this time scale is low. On the other hand, it is possible to make a phenomenological correlation.…”

Estimation of changes in the composition of the Martian atmosphere caused by CO2 condensation from GRS Ar measurements and its application to the rederivation of MGS radio occultation measurements

“…Temperatures markedly lower than the frost point of CO 2 have been observed in the winter polar region; these are called “cold spots” [ Kieffer et al , ]. Cold spots are not fully understood, and even after more than a quarter of a century of study, much effort is focused on explaining them [ Weiss and Ingersoll , ; Titus et al , ; Cornwall and Titus , , ; Hayne et al , ].…”