First Detection of the Pekeris Internal Global Atmospheric Resonance:
Evidence from the 2022 Tonga Eruption and from Global Reanalysis Data
Abstract
We used observations and model simulation to examine the atmospheric
pulses that dominate the far field in the hours after the January 2022
Tonga eruption. We analyzed radiance observations taken from the
Himawari-8 geostationary satellite and showed that both a Lamb wave
front with the expected horizontal phase speed ~315
m-s-1 and a distinct front with phase speed ~245 m-s-1
can be detected. The slower phase speed is consistent with that expected
for the global internal resonant mode that had been proposed by Pekeris
in 1937 and in other idealized theoretical studies over the past
century, but which had never been detected in the atmosphere. A
simulation of the eruption aftermath was performed with a high
resolution atmospheric general circulation model. A hot anomaly over the
volcano location was introduced instantaneously to the model fields and
the model was integrated for another 12 hours. This produced a simulated
wave pulse that, in the far field, agreed reasonably well with barograph
observations of the Lamb wave. The model results also showed the
presence of the slower pulse and that this disturbance had a vertical
structure with a 180o phase shift in the stratosphere, in agreement with
the theoretical prediction for the internal mode. An implication of this
result is that the continuously ringing Lamb wave global normal modes
that have been seen in analysis of long observational records ought to
have lower frequency internal Pekeris mode counterparts, a prediction
that we confirm though analysis of 57 years of hourly global reanalysis
data.