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  • Author or Editor: R. S. Lieberman x
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Elsayed R. Talaat and Ruth S. Lieberman

Abstract

This paper presents analyses of nonmigrating diurnal tide signatures in High Resolution Doppler Imager mesospheric and lower-thermospheric winds and temperatures. A global comparison of both winds and temperature reveals equatorial features corresponding to nonmigrating tides. Structures interpreted as zonal mean and eastward nonmigrating diurnal tides display consistency between horizontal winds and temperatures. The second symmetric mode is prominent in the zonal mean and wavenumber 1. The gravest antisymmetric mode and the gravest symmetric or Kelvin mode are the main features in zonal wavenumbers 2 and 3. The amplitudes of the tides generally increase with altitude and maximize within 90–110 km.

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R. S. Lieberman, J. France, D. A. Ortland, and S. D. Eckermann

Abstract

Recent studies suggest linkages between anomalously warm temperatures in the winter stratosphere, and the high-latitude summer mesopause. The summer temperature anomaly is manifested in the decline of polar mesospheric clouds. The 2-day wave is a strong-amplitude and transient summer feature that interacts with the background state so as to warm the high-latitude summer mesopause. This wave has been linked to a low-latitude phenomenon called inertial instability, which is organized by breaking planetary waves in the winter stratosphere. Hence, inertial instability has been identified as a possible nexus between the disturbed winter stratosphere, and summer mesopause warming. We investigate a sustained occurrence of inertial instability during 19 July–8 August 2014. During this period, stratospheric winter temperatures warmed by about 10 K, while a steep decline in polar mesospheric clouds was reported between 26 July and 6 August. We present, for the first time, wave driving associated with observed inertial instability. The effect of inertial instability is to export eastward momentum from the winter hemisphere across the equator into the summer hemisphere. Using a primitive equation model, we demonstrate that the wave stresses destabilize the stratopause summer easterly jet. The reconfigured wind profile excites the wavenumber-4 component of the 2-day wave, leading to enhanced warming of the summer mesopause. This work supports previous numerical investigations that identified planetary wave–driven inertial instability as a source of the 2-day wave.

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R. S. Lieberman, W. A. Robinson, S. J. Franke, R. A. Vincent, J. R. Isler, D. C. Fritts, A. H. Manson, C. E. Meek, G. J. Fraser, A. Fahrutdinova, W. Hocking, T. Thayaparan, J. MacDougall, K. Igarashi, T. Nakamura, and T. Tsuda

Abstract

High Resolution Doppler Imager (HRDI) measurements of daytime and nighttime winds at 95 km are used to deduce seasonally averaged Eulerian mean meridional winds during six solstice periods. These estimates are compared with seasonally averaged radar meridional winds and with results from dynamical and empirical wind models. HRDI mean meridional winds are directed from the summer pole toward the winter pole over much of the globe. Peak equatorward winds of about 15 m s−1 are usually observed in the summer hemisphere near 30°. A local minimum in the equatorward winds is often observed poleward of this latitude, with winds approaching zero or reversing direction. A similar structure is seen in contemporaneous radar winds. This behavior differs from residual meridional wind patterns predicted by models. The discrepancies may be related to gravity wave paramaterizations or a consequence of planetary wave influences.

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