Abstract
Abstract. Using 11-year-long K Doppler lidar observations of temperature profiles in the mesosphere and lower thermosphere (MLT) between 85 and 100 km, conducted at the Arecibo Observatory, Puerto Rico (18.35∘ N, 66.75∘ W), seasonal variations of mean temperature, the squared Brunt–Väisälä frequency, N2, and the gravity wave potential energy (GWPE) are estimated in a composite year. The following unique features are obtained. (1) The mean temperature structure shows similar characteristics to an earlier report based on a smaller dataset. (2) Temperature inversion layers (TILs) occur at 94–96 km in spring, at ∼92 km in summer, and at ∼91 km in early autumn. (3) The first complete range-resolved climatology of GWPE derived from temperature data in the tropical MLT exhibits an altitude-dependent combination of annual oscillation (AO) and semiannual oscillation (SAO). The maximum occurs in spring and the minimum in summer, and a second maximum is in autumn and a second minimum in winter. (4) The GWPE per unit volume reduces below ∼97 km altitude in all seasons. The reduction of GWPE is significant at and below the TILs but becomes faint above; this provides strong support for the mechanism that the formation of upper mesospheric TILs is mainly due to the reduction of GWPE. The climatology of GWPE shows an indeed pronounced altitudinal and temporal correlation with the wind field in the tropical mesopause region published in the literature. This suggests the GW activity in the tropical mesopause region should be manifested mainly by the filtering effect of the critical level of the local background wind and the energy conversion due to local dynamical instability.
Highlights
Gravity waves (GWs) are believed to be the primary force driving the large-scale circulation and coupling of different atmospheric layers due to their momentum and energy deposition when breaking or dissipating (Fritts and Alexander, 2003; Lindzen, 1981; Smith, 2012)
(3) The first complete range-resolved climatology of gravity wave potential energy (GWPE) derived from temperature data in the tropical mesosphere and lower thermosphere (MLT) exhibits an altitude-dependent combination of annual oscillation (AO) and semiannual oscillation (SAO)
In the following the results of the analysis are shown and discussed with respect to the seasonal variation of the mean temperature (Sect. 4.1), the square of the Brunt–Väisälä frequency (Sect. 4.2), and the GW activity (Sect. 4.3)
Summary
Gravity waves (GWs) are believed to be the primary force driving the large-scale circulation and coupling of different atmospheric layers due to their momentum and energy deposition when breaking or dissipating (Fritts and Alexander, 2003; Lindzen, 1981; Smith, 2012). GWs often originate from copious tropospheric sources and propagate upward. Their amplitudes grow rapidly with altitude under the condition of decreasing atmospheric density. GWs begin to break or dissipate in the mesosphere and lower thermosphere (MLT), where their influences have been shown to be strong by various observations (e.g., Baumgarten et al, 2015, 2017, 2018; Cai et al, 2014; Gardner and Liu, 2010; Li et al, 2010; Lu et al, 2009; Yuan et al, 2016). Associated modeling studies have shown that including the effects of GWs is a key point in the simulation of realistic quasi-biennial and semiannual oscillations and other phenomena in the stratosphere and mesosphere (e.g., Dunkerton, 1982; Huang et al 2010; Xu et al, 2006)
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