Ertel potential vorticity versus Bernoulli streamfunction on Mars

Dowling, T. E.; Bradley, M. E.; Du, J.; Lewis, S. R. and Read, P. L. (2017). Ertel potential vorticity versus Bernoulli streamfunction on Mars. Quarterly Journal of the Royal Meteorological Society, 143(702) pp. 37–52.

DOI: https://doi.org/10.1002/qj.2916

Abstract

Scatter plots of Ertel potential vorticity, Q, versus Bernoulli streamfunction, B, on potential-temperature surfaces, θ, are investigated for Mars using the global Mars Analysis Correction Data Assimilation (MACDA) reanalysis, which spans Mars Year (MY) 24.39 to 27.24. In mid-latitudes, Mars exhibits monotonic, function-like Q(B) correlations on θ surfaces similar to those observed for Earth. We quantify this with linear regressions of Q versus B over the vertical range θ = 400 to 900K (~30 to 60 km). In autumn, winter and spring, in both hemispheres, the nondimensionalized correlation generally lies between zero and unity and gradually decreases with height, whereas in northern summer, it swings negative. These characteristics match Earth's lower mesosphere (θ = 2000 to 3000 K; z≈ 48 to 62 km) during the same seasons. The exception is southern summer, when the correlation on Mars nearly vanishes. In time series, the transition into and out of northern summer is sinuous and centred just after solar longitude Ls = 90°, whereas in southern summer it is abrupt and spans ΔLs≈120°, which is 1/3 of a Mars year. A striking feature seen on Mars but not on Earth is a large range of Q over the narrow domain of B poleward of each winter polar jet, particularly in the north, which is consistent with the known annular structure of the Martian polar vortex. Froude number calculations suggest the existence of a planetary-scale hydraulic jump associated with the winter polar jet.

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