Response of convectively coupled Kelvin waves to surface temperature
forcing in aquaplanet simulations
Abstract
This study investigates changes in the propagation and maintenance of
convectively coupled Kelvin waves (KWs) in response to surface warming.
We use a set of three aquaplanet simulations made with the Community
Atmospheric Model version 6 by varying the sea surface temperature
boundary conditions, representing the current climate, a warmer (+4K),
and a cooler (-4K) climate. Results show that KWs accelerate at the rate
of about 7.1%/K and their amplitudes decrease by 4.7%/K. The dampening
of KWs with warming is found to be associated with a weakening of the
internal thermodynamic feedback between diabatic heating and temperature
anomalies that generates KW eddy available potential energy (EAPE). The
phase speed of KWs closely matches that of the second baroclinic mode KW
in -4K, while the phase speed of KWs is approximately that of the first
baroclinic mode KW in +4K. Meanwhile, the coupling between the two
baroclinic modes weakens with warming. We hypothesize that in -4K, as
the first and second modes are strongly coupled, KWs destabilize by
positive EAPE generation within the second mode, and they propagate
slower following the second mode KW phase speed. In +4K, as the first
and second modes decouple, KWs are damped by negative EAPE generation
within the first mode, and they propagate faster following the first
mode KW phase speed.