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. The existing distribution of meteor radars located from high- tolow-latitude regions provides a favorable temporal and spatial coverage forinvestigating the climatology of the global mesopause density. In thisstudy, we report the climatology of the mesopause relative density estimatedusing multiyear observations from nine meteor radars, namely, the DavisStation (68.6 ∘  S, 77.9 ∘  E), Svalbard (78.3 ∘  N,16 ∘  E) and Tromso (69.6 ∘  N, 19.2 ∘  E) meteorradars 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 in the midlatitudes; and theKunming (25.6 ∘  N, 103.8 ∘  E) and Darwin (12.3 ∘  S, 130.8 ∘  E) meteor radars located at low latitudes. The dailymean relative density was estimated using ambipolar diffusion coefficientsderived from the meteor radars and temperatures from the Microwave LimbSounder (MLS) on board the Aura satellite. The seasonal variations in theDavis Station meteor radar relative densities in the southern polarmesopause are mainly dominated by an annual oscillation (AO). The mesopauserelative densities observed by the Svalbard and Tromso meteor radars athigh latitudes and the Mohe and Beijing meteor radars at high midlatitudesin the Northern Hemisphere show mainly an AO and a relatively weaksemiannual oscillation (SAO). The mesopause relative densities observed bythe Mengcheng and Wuhan meteor radars at lower midlatitudes and the Kunmingand Darwin meteor radars at low latitudes show mainly an AO. The SAO isevident in the Northern Hemisphere, especially at high latitudes, and itslargest amplitude, which is detected at the Tromso meteor radar, iscomparable to the AO amplitudes. These observations indicate that themesopause relative densities over the southern and northern high latitudesexhibit a clear seasonal asymmetry. The maxima of the yearly variations inthe mesopause relative densities display a clear latitudinal variationacross the spring equinox as the latitude decreases; these latitudinalvariation characteristics may be related to latitudinal changes influencedby gravity wave forcing. In addition to an AO, the mesopause relativedensities over low latitudes also clearly show an intraseasonal variationwith a periodicity of 30–60  d .

Climatology of the mesopause relative density using a global distribution of meteor radars