Equatorial waves, diurnal tides and small-scale thermal variability in
the tropical lower stratosphere from COSMIC-2 radio occultation
Abstract
A new constellation of radio occultation satellites called COSMIC-2
(Constellation Observing System for Meteorology, Ionosphere and
Climate-2) is providing unprecedented dense measurements of the tropical
atmosphere, with on average more than 4,000 high quality observations
per day over 40o N-S. We use these data to evaluate
large- and small-scale thermal variability in the tropical lower
stratosphere during October 2019 – April 2020. Space-time spectral
analysis of gridded COSMIC-2 data reveals a rich spectrum of traveling
planetary-scale waves, including Kelvin waves, mixed Rossby-gravity
waves and inertia gravity waves, in addition to propagating diurnal
tides. These coherent modes show enhanced amplitudes from the tropical
tropopause through the lower stratosphere (~17-25 km).
Characteristics of small-scale temperature variances, calculated as
deviations from the gridded fields, reveal systematic spatial patterns
including time average maxima over Africa and South America overlying
persistent deep convection. Small-scale variances also exhibit transient
maxima in the equatorial lower stratosphere tied to large-scale Kelvin
waves. The new COSMIC-2 observations provide novel details on the rich
spectrum of large- and small-scale waves near and above the tropical
tropopause.