Dataset Information

Cross-Equatorial Flushing Dust Storms and Northern Hemisphere Transient Eddies: An Analysis for Mars Year 24.

ABSTRACT: The relationship between frontal/flushing dust storms and northern hemisphere synoptic period transient eddies in Mars year 24 is examined in this paper. Frontal dust storms are observed roughly continuously during the presolstice (early/middle fall) and postsolstice (middle/late winter) time periods, but flushing dust storms that cross the equator are confined to shorter seasonal windows on both sides of the solsticial pause. In the lower atmosphere, the timing of cross-equatorial flushing dust storms correlates better with eddy temperature than with eddy meridional wind; in the middle atmosphere, it correlates better with eddy meridional wind than with eddy temperature. This is because both the lower atmosphere eddy temperature and the middle atmosphere eddy meridional wind are dominated by zonal wave number m = 3 eastward traveling waves during the cross-equatorial flushing dust storm periods. Frontal dust storms do not seem to be limited to any particular wave mode, but cross-equatorial flushing dust storms appear to be closely related to m = 3 eastward traveling waves, at least in Mars year 24. The effectiveness of m = 3 waves in this regard is partially due to their amplitudes but more importantly due to their seasonal distributions and latitudinal positions. During the time periods when m = 3 waves are strong, the m = 3 waves are also located at lower latitudes, closer in distance to the fairly strong southward mean meridional wind in the low latitudes. Dust in frontal dust storms at high latitudes can be easily entrained into the low-latitude circulation and be efficiently transported southward.

SUBMITTER: Wang H

PROVIDER: S-EPMC6662229 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature

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Publications

Cross-Equatorial Flushing Dust Storms and Northern Hemisphere Transient Eddies: An Analysis for Mars Year 24.

Wang H H

Journal of geophysical research. Planets 20180619 7

The relationship between frontal/flushing dust storms and northern hemisphere synoptic period transient eddies in Mars year 24 is examined in this paper. Frontal dust storms are observed roughly continuously during the presolstice (early/middle fall) and postsolstice (middle/late winter) time periods, but flushing dust storms that cross the equator are confined to shorter seasonal windows on both sides of the solsticial pause. In the lower atmosphere, the timing of cross-equatorial flushing dust ...[more]

PMID: 31360622

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Project description:The climatology of baroclinic waves in the northern hemisphere of Mars is investigated through analysis of observations by the infrared sounders on Mars Reconnaissance Orbiter (MRO) and Mars Global Surveyor (MGS). We focus on the lowest scale height above the surface, where the waves have a large impact on the Martian dust cycle. Profiles retrieved by the MRO Mars Climate Sounder (MCS) rarely reach the lower atmosphere at the season and location of interest. To fill this gap, we turn to observations in the MCS B1 channel (32 microns) when the instrument is viewing the surface. The signature of baroclinic waves appears in these data because of dust-related emission from the lower atmosphere and wave-induced variations of surface temperature. We supplement the MCS data with measurements of temperature at the 610-Pa pressure level from the MGS Thermal Emission Spectrometer (TES). Both data sets provide systematic coverage in latitude and longitude at two local times. Characteristics of baroclinic waves are derived through analysis of observations with a combined duration of about 8 Mars years. Basic results include least-squares solutions for wave amplitude and period at zonal wavenumber 1-3; the resolution is 4° in latitude and 14 solar days in time of observation. There is a strong similarity between the baroclinic waves observed by MCS and TES, which confirms the sensitivity of the MCS B1 channel to wave activity at pressures near 610 Pa. In all 8 Mars years, the baroclinic waves exhibit periodic transitions among modes with different zonal wavenumbers and a distinctive solstitial pause. Although the weather in each Mars year is unique in some respects, a composite of results from all years reveals a well-defined wave climatology. At each zonal wavenumber, large amplitudes are restricted to a pair of seasonal windows positioned symmetrically about the winter solstice. The wave-2 mode is strongest in early autumn and near the vernal equinox, whereas wave 3 is the dominant mode in mid-autumn and mid-winter, immediately before and after the solstitial pause. The interaction between baroclinic waves and dust storms is investigated through comparisons with spacecraft measurements of dust opacity. A strong wave-3 mode is often present during the initial growth phase of large, seasonal dust storms, which reflects the importance of wave-generated frontal dust storms in triggering these events. The wave-3 amplitude then decreases rapidly as the dust storm evolves; this occurs routinely in all Mars years considered here in connection with both mid-autumn "A" storms and mid-winter "C" storms. In some years A-storm suppression of the wave-3 mode marks the beginning of the solstitial pause. These results provide a basis for testing and development of Mars General Circulation Models as well as context for interpreting contemporaneous observations, such as spacecraft images of frontal and flushing dust storms.

Dataset Information

Cross-Equatorial Flushing Dust Storms and Northern Hemisphere Transient Eddies: An Analysis for Mars Year 24.

Publications

Cross-Equatorial Flushing Dust Storms and Northern Hemisphere Transient Eddies: An Analysis for Mars Year 24.

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