Spatiotemporal Distribution of Kelvin Wave Amplitudes in the Tropical Tropopause Layer (TTL) From GNSS RO Measurements

Abstract This paper presents the spatiotemporal distributions of the tropical tropopause layer (TTL) Kelvin wave (KW) amplitudes by using the global navigation satellite sstem (GNSS) radio occultation (RO) data sets of 2007–2020. The results show that the longitudinal variations of TTL KWs during different seasons are primarily driven by zonal winds rather than static stability. Investigations on the annual variations of TTL KWs reveal that below the tropopause, TTL KWs reach the maxima during June, July, and August (JJA) and the minima during December, January, and February (DJF) over 150°E–240°E (Pacific Ocean (PO)) and 270°E–360°E (Atlantic Ocean; AO), where zonal winds and static stability present similar annual variations, while over 30°E–120°E (Indian Ocean; IO), zonal winds and static stability present different annual variations, resulting in weakened KW annual variation. Above the tropopause, TTL KWs generally reach the maxima during DJF and the minima during JJA, which is mainly modulated by static stability. El Niño‐Southern Oscillation (ENSO) modulates the longitudinal distribution of TTL KWs by affecting the zonal winds, leading to that strong TTL KWs present broader longitudinal distribution during El Niño than during La Niña. El Niño‐Southern Oscillation also affects the vertical distribution of TTL KWs by static stability, resulting in weaker (stronger) KWs below the tropopause and stronger (weaker) KWs above the tropopause during La Niña (El Niño) over 90°E–180°E. The opposite process occurs over 180°E–270°E. Quasi‐biennial oscillation (QBO) may affect the interannual variations of TTL KWs above around 18 km by affecting zonal winds and static stability, leading to TTL KWs reach the maxima before westerly shears occur.