Nonmigrating tidal heating and MLT tidal wind variability due to the El Niño–Southern Oscillation

Abstract

Tides forced by large‐scale weather systems in the tropical troposphere introduce significant longitudinal and local time variability in the upper atmosphere. This paper presents variability of tidal harmonics of the latent heating from 2002 to 2011 associated with the El Niño–Southern Oscillation (ENSO) and the tidal wind response in the mesosphere/lower thermosphere (MLT) region. Emphasis is on the strong ENSO cycle 2009–2011. Latent tidal heating rates are computed from TRMM satellite precipitation data, with added radiative heating from MERRA reanalysis, as functions of time, latitude, and altitude. The heating rates for the two most affected nonmigrating tides (DE3 and DE2) are examined and compared with MLT tidal wind variability from TIDI/TIMED. Principal component analysis (PCA) is used to identify the tidal modes most affected by ENSO. Our results indicate that the tidal response to ENSO is largest during winter for both of the tides, with the largest response occurring in the DE3 tidal winds during the La Niña phase, with an increase of roughly 70% for the winter months of 2010/2011, and negligible response during the El Niño phase. The ENSO effect in the tidal forcing closely resembles the first symmetric and antisymmetric Hough modes of DE3 and DE2, thus being an efficient mechanism to transmit the ENSO signal into the MLT tides.