Abstract
AbstractThis paper examines the response of the upper atmosphere to equatorial Kelvin waves with a period of ∼3 days, also known as ultrafast Kelvin waves (UFKWs). The whole atmosphere model Ground‐to‐topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) is used to simulate the UFKW events in the late summer of 2010 and 2011 as well as in the boreal winter of 2012/2013. When the lower layers of the model below 30‐km altitude are constrained with meteorological data, GAIA is able to reproduce salient features of the UFKW in the mesosphere and lower thermosphere as observed by the Aura Microwave Limb Sounder. The model also reproduces ionospheric response, as validated through comparisons with total electron content data from the Gravity field and steady‐state Ocean Circulation Explorer satellite as well as with earlier observations. Model results suggest that the UFKW produces eastward‐propagating ∼3‐day variations with zonal wavenumber 1 in the equatorial zonal electric field and F region plasma density. Model results also suggest that for a ground observer, identifying ionospheric signatures of the UFKW is a challenge because of ∼3‐day variations due to other sources. This issue can be overcome by combining ground‐based measurements from different longitudes. As a demonstration, we analyze ground‐based magnetometer data from equatorial stations during the 2011 event. It is shown that wavelet spectra of the magnetic data at different longitudes are only in partial agreement, with or without a ∼3‐day peak, but a spectrum analysis based on multipoint observations reveals the presence of the UFKW.
Highlights
Equatorial Kelvin waves are a type of global‐scale waves in the atmosphere
We examine the ultrafast Kelvin waves (UFKWs) events of September 2010, August–September 2011, and December 2012 to January 2013, which are strong according to the 16 years of geopotential height (GPH) measurements by the Aura Microwave Limb Sounder (MLS) (Figure 1)
As we constrain the lower layers of GAIA below 30 km with meteorological reanalysis data, the model is able to reproduce main characteristics of UFKWs in the mesosphere and lower thermosphere (MLT) region as observed by the Aura/MLS (Figures 2–5)
Summary
Equatorial Kelvin waves are a type of global‐scale waves in the atmosphere. Equatorial Kelvin waves propagate vertically upward from the source region in the troposphere where they are thought to be excited by latent heating due to tropical convection. They are often classified into three categories according to the wave period (and the zonal phase speed): slow Kelvin waves with periods 10–20 days, fast Kelvin waves with periods 5–10 days, and ultrafast Kelvin waves (UFKWs) with periods 2–5 days. As the wave propagates to higher altitudes, it grows in amplitude due to the reduction in atmospheric density. UFKWs can be a significant source of wave forcing in the upper atmosphere among other global‐scale waves such as tides and planetary waves (Liu, 2016; Yiğit & Medvedev, 2015)
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