Tropical Temperature Variability in the UTLS: New Insights from GPS Radio Occultation Observations

Abstract

Global Positioning System (GPS) radio occultation (RO) observations, first made of Earth’s atmosphere in 1995, have contributed in new ways to the understanding of the thermal structure and variability of the tropical upper troposphere–lower stratosphere (UTLS), an important component of the climate system. The UTLS plays an essential role in the global radiative balance, the exchange of water vapor, ozone and other chemical constituents between the troposphere and stratosphere, and the transfer of energy from the troposphere to the stratosphere. With their high accuracy, precision, vertical resolution, and global coverage, RO observations are uniquely suited for studying the UTLS and a broad range of equatorial waves, including gravity waves, Kelvin waves, Rossby and mixed Rossby gravity waves, and thermal tides. Because RO measurements are nearly unaffected by clouds, they also resolve the upper-level thermal structure of deep convection and tropical cyclones, as well as volcanic clouds. Their low biases and stability from mission to mission make RO observations powerful tools for studying climate variability and trends, including the annual cycle and intra-seasonal to inter-annual atmospheric modes of variability such as the quasi-biennial oscillation (QBO), Madden-Julian oscillation (MJO), and El Niño-Southern oscillation (ENSO). These properties also make them useful for evaluating climate models and detection of small trends in the UTLS temperature, key indicators of climate change. This paper reviews the contributions of RO observations to the understanding of the three-dimensional structure of tropical UTLS phenomena and their variability over time scales ranging from hours to decades and longer.

Observing the climate impact of large wildfires on stratospheric temperature

“…Radio occultation (RO) temperature data which offers high accuracy, very good vertical resolution in the upper troposphere and lower stratosphere (UTLS) region, and global coverage 30 – 32 , are taken from the Wegener Center (WEGC) occultation processing system version 5.6 (OPSv5.6) multi-satellite record 33 .…”

Continuous rise of the tropopause in the Northern Hemisphere over 1980–2020

“…The satellite-based GPS RO data have provided continuous temperature and pressure measurements as a function of height in the upper troposphere and lower stratosphere with high accuracy, high vertical resolution, and global coverage since 2001 (49)(50)(51). We used the latest Wegener Center (WEGC) multisatellite GPS RO data, OPSv5.6, available from May 2001 to December 2020.…”

Equatorial Waves, Diurnal Tides and Small‐Scale Thermal Variability in the Tropical Lower Stratosphere From COSMIC‐2 Radio Occultation

“…An important aspect of equatorial waves is their relatively narrow vertical scales (typical vertical wavelengths of ∼4–8 km), so that high vertical resolution is important for satellite measurements. Temperature retrievals from Global Navigation Satellite System (GNSS) radio occultation (RO) have UTLS vertical resolution of ∼1 km or better (Zeng et al., 2019), with horizontal (along‐track) resolution of ∼200 km, and global measurements since ∼2002 have provided characterization of equatorial wave structure and long‐term variability (e.g., Alexander et al., 2008; Kim & Son, 2012; Randel & Wu, 2005; Scherllin‐Pirscher et al., 2017, 2021; Tsai et al., 2004). Complementary studies with other high resolution satellite data were provided by Alexander and Ortland (2010) and Ern et al.…”