Variability of mesospheric diurnal tides and tropospheric diurnal heating during 1997–1998

Abstract

[1] This study focuses on interannual variations of diurnal tropospheric heating and the response in the mesosphere observed by radars and predicted by a model. The work is prompted by reports of interannual variability in amplitudes of tidal variables at low latitudes. Diurnal tides observed at Hawaii and Christmas Island exhibit a pronounced ''spike'' in amplitude from late 1997 to early 1998. It has been speculated that this variability may be linked to the El Niño-Southern Oscillation phenomenon. We examine diurnal solar heating due to water vapor absorption, and diurnal latent heat release due to deep convection between 1988 and 2005. Both of these heating drives exhibit anomalously higher amplitudes in the tropical central and eastern Pacific during 1997-1998. The altered heating patterns result in a stronger forcing of the migrating diurnal tide by water vapor heating, and excitation of several weaker nonmigrating modes by latent heating. A primitive equation model is used to evaluate how these drives contribute to diurnal winds in the mesosphere. Anomalous water vapor heating results in about 15% increases in model meridional wind amplitudes over climatological values at subtropical latitudes between 300°E and the Greenwich meridian. While the timing of the model amplitude enhancements is consistent with observations at Hawaii, the observed increases are significantly stronger. Our study indicates that water vapor heating is the larger contributor to tidal enhancement observed during 1997-1998.

The diurnal and semidiurnal tides over Ascension Island (° S, 14° W) and their interaction with the stratospheric quasi-biennial oscillation: studies with meteor radar, eCMAM and WACCM

“…This is particularly interesting when contrasted with the enhanced diurnal amplitudes in the MLT observed during El Niño events, i.e. positive correlations, at various ground-based stations in the Pacific (Tirunelveli, Jakarta, Kauai, and Christmas Island) as observed by Gurubaran et al (2005) and Lieberman et al (2007). This is the opposite of the effect we observe over Ascension Island.…”

Thermospheric inter-annual variability and its potential connection to ENSO and stratospheric QBO

“…Since absorption of solar heating by water vapor is the major source for tidal generation, changes in precipitation patterns will change the global distribution of water vapor and hence lead to changes in atmospheric tides. Indeed, there have been many studies showing an increase in the diurnal tides amplitude during ENSO period from both observational (Gurubaran et al 2005;Lieberman et al 2007) and model simulations (Lieberman et al 2007;Liu 2012, 2013). It is known that both migrating and non-migrating diurnal tides can propagate upward to the thermosphere and cause perturbations in the thermospheric density (Liu et al 2009(Liu et al , 2014Yamazaki and Richmond 2013).…”

Global Dynamics of the MLT

“…The phase of the QBO in WACCM tides agrees with that observed. Lieberman et al (2007) investigated the response of the DW1 tide to large-scale interannual changes in the diurnal component of tropospheric water heating associated with an El Niño event in the tropical ocean/atmosphere. The heating changes include both the absorption of radiation by water vapor and latent heat release.…”