Climatology of mesopause density using a global distribution of meteor radars

The existing distribution of meteor radars, located from high to low latitude regions, permits an estimate of global mesopause density, and provides a favorable temporal and spatial coverage for examining the climatology of global mesopause density. In this study, we report a climatology of mesopause density estimated using multiyear observations from the meteor radars at Davis Station (68.6°S, 77.9°E), Svalbard (78.3°N, 16°E) and Tromsø (69.6°N, 19.2°E), which are located at high latitudes; the Mohe (53.5°N, 122.3°E), Beijing (40.3°N, 116.2°E), Mengcheng (33.4°N, 116.6°E) and Wuhan (30.5°N, 114.6°E) meteor radars, located at midlatitudes; the Kunming (25.6°N, 103.8°E) and Darwin (12.3°S, 130.8°E) meteor radars, located at low latitudes. The daily mean density was estimated using the ambipolar diffusion coefficients from the meteor radars and temperatures from the Microwave Limb Sounder (MLS) on the Aura satellite. The seasonal variations of the Davis meteor radar densities in southern polar mesopause mainly show a domination of annual oscillation (AO). The mesopause densities observed by the Svalbard and Tromsø meteor radars at high latitudes, the Mohe and Beijing meteor radars at high midlatitudes in northern hemisphere mainly show an AO and a relative weak semiannual oscillation (SAO). The mesopause densities observed by the Mengcheng and Wuhan meteor radars at lower mid-latitudes and the Kunming and Darwin meteor radars in low latitudes mainly show an AO. The SAO is evident in northern hemisphere especially in the high latitudes, and has the largest amplitude at Tromsø which is comparable to the AO amplitude. The observations indicate that the mesopause densities over southern and northern high latitudes show a clear seasonal asymmetry. The maxima of the yearly variations in mesopause densities have a clear temporal variation, across forward the spring equinox, as the latitude decrease; these latitude variation characteristic may relate to the latitudes changes of the gravity wave forcing. In addition to the AO, the mesopause densities over low latitudes also clearly show a periodicity of 30-60 days variability, which relate to the Madden-Julian Oscillations in subtropics troposphere.