Observational Evidence for the Influence of Diurnal Tide in Driving Winds in the Polar Upper Mesosphere and Lower Thermosphere

Abstract

The dynamics of the upper mesosphere and lower thermosphere (UMLT) region is largely influenced by atmospheric solar tides, in addition to gravity waves (GWs) and planetary waves (PWs) that vary at different spatial and temporal scales. The atmospheric solar tides are global scale oscillations having periods, which are sub-harmonics of a solar day, that is, 24, 12, 8, 6 hr and so on. These tides are considered as important dynamical entities responsible for the transmission and deposition of energy from the lower atmosphere to the UMLT region. They play an important role in coupling the lower atmosphere to the mesosphere-ionosphere-thermosphere system. When they propagate upward, their amplitudes increase exponentially because of the decrease of atmospheric density with height. After the attainment of maximum amplitude in the UMLT region, they undergo dissipation. The dissipation can either be mechanical dissipation, like viscosity and turbulence or thermal dissipation, like thermal conduction and infrared cooling (Teitelbaum and Vial., 1981). The tides are classified into migrating and non-migrating components. The migrating tides propagate westward with the apparent motion of the sun and vary only with local time. They are mostly generated by the heating due to the absorption of solar radiation by water vapor in the troposphere, ozone in the stratosphere, and nitrogen and oxygen in the thermosphere. However, the non-migrating tides depend both on local time and longitude (Chapman & Lindzen, 1970;Li et al., 2020) and they can propagate westward, eastward or remain stationary. Longitudinal asymmetry of

Long‐Term Variability and Tendencies in Mesosphere and Lower Thermosphere Winds From Meteor Radar Observations Over Esrange (67.9°N, 21.1°E)

“…From the above studies, it is evidenced that the MLT winds are significantly modulated by the solar forcing and lower atmospheric perturbations. Most of the studies on long-term tendencies in the MLT winds are from equatorial/low-latitudes (Burrage et al, 1996;Gurubaran & Rajaram, 1999;Kishore Kumar et al, 2014;Rajaram & Gurubaran, 1998;Sridharan et al, 2007Sridharan et al, , 2010Venkateswara Rao et al, 2012) along with short-term variabilities (K. K. Kumar et al, 2007Kumar et al, , 2008Rao et al, 2014), and mid-latitudes (Jacobi, 2012;Jacobi et al, 2005Jacobi et al, , 2012Jacobi et al, , 2015Namboothiri et al, 1993Namboothiri et al, , 1994Portnyagin et al, 2006); however the trends and variabilities in the high-latitude (including Arctic and Antarctic) MLT winds are very limited (Baumgaertner et al, 2005;Dempsey et al, 2021;Dutta & Sridharan, 2023;Hindley et al, 2022;Jaen et al, 2023;Lukianova et al, 2015Lukianova et al, , 2018Mitchell et al, 2002;Venkateswara Rao et al, 2015) from various observations and model simulations. Global variabilities in the MLT winds can be found at Ramesh et al (2020a), X.…”