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The Martian Slope Winds and the Nocturnal PBL Jet

Hannu SavijärviDepartment of Meteorology, University of Helsinki, Helsinki, Finland

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Tero SiiliFinnish Meteorological Institute, Helsinki, Finland

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Abstract

The summertime Martian PBL diurnal wind variation, slope winds, and the nocturnal low-level jets were studied using Prandtl's theory, a mesoscale numerical model, and Viking lander observations. During moderate prevailing large-scale flow, nocturnal jets were simulated that were rather similar to those on Earth. They were mainly caused by inertial oscillation after sunset with some contribution from the slope wind effects over sloping regions (which are very common in Mars). During weak large-scale flow, shallow nocturnal drainage flows with strong vertical shear developed over the cold Martian slopes. At middle and high latitudes, these katabatic winds tended to turn to flow along the slope by dawn (due to the Coriolis force). For sufficiently steep slopes, near-surface drainage winds could reach considerable speeds. In contrast, the typical afternoon upslope winds were vertically homogeneous up to 2–3 km and weak (only 1–3 m s−1 in magnitude), even over relatively steep large-scale slopes.

Abstract

The summertime Martian PBL diurnal wind variation, slope winds, and the nocturnal low-level jets were studied using Prandtl's theory, a mesoscale numerical model, and Viking lander observations. During moderate prevailing large-scale flow, nocturnal jets were simulated that were rather similar to those on Earth. They were mainly caused by inertial oscillation after sunset with some contribution from the slope wind effects over sloping regions (which are very common in Mars). During weak large-scale flow, shallow nocturnal drainage flows with strong vertical shear developed over the cold Martian slopes. At middle and high latitudes, these katabatic winds tended to turn to flow along the slope by dawn (due to the Coriolis force). For sufficiently steep slopes, near-surface drainage winds could reach considerable speeds. In contrast, the typical afternoon upslope winds were vertically homogeneous up to 2–3 km and weak (only 1–3 m s−1 in magnitude), even over relatively steep large-scale slopes.

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