On the Temperature-Depleted Layer at 30-36 km Altitude Observed by High-Altitude Radiosonde Observations in Okinawa in September 2022

Since the end of continuous rocket-sonde observations, which had been conducted until the 1990s, direct observations at altitudes higher than 30 km have been conducted only intermittently, so there are fewer observation data than in lower altitude regions.

In the present study, we conducted radiosonde observations with large rubber balloons to obtain vertical structures of wind velocity and temperature at altitudes higher than 30 km from 27 September to 3 October 2022 at the University of the Ryukyus, Okinawa Island, Japan.

During the observation period, temperatures from 20 to 40 km altitude basically increased monotonically, including small perturbations. However, an observation at 1730 JST on 28 September showed a remarkable continuous decrease with altitude in temperature at 30-36 km altitude. This was also confirmed by Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC)-2 GNSS-RO temperature data observed near Okinawa Island and ERA5 reanalysis data. Using the ERA5 reanalysis and radiosonde observation data, we found that the temperature-depleted layer is caused by a planetary-scale wave and upward energy propagating inertia gravity wave.