Rossby Wave Activity in the Extratropical UTLS and Its Impact on Extreme Temperature Events: Insights From GNSS RO Measurements

The Global Navigation Satellite System (GNSS) radio occultation (RO) data during 2007–2020 is used to study the Rossby wave (RW) activity in the upper troposphere and lower stratosphere (UTLS) between 6 and 16 km over the extratropical regions. An existing method for deriving RW phase speed (RWPS) is modified so that it can be applied to RO data set, and the RO‐derived RW envelopes (RWEs) and RWPSs are verified using reanalysis data. Spatiotemporal variations of RWs and background mechanisms are investigated, and the relationship between RWs and surface extreme temperature events (ETEs) is analyzed. In the northern hemisphere, both RWE and RWPS are weakened during June–August (JJA), and are strengthened during December–February (DJF). While in the southern hemisphere, RWE is amplified during March–May (MAM). Both RWE and RWPS reach the maxima around the tropopause height, and during all seasons, the spatiotemporal distributions of RWEs and RWPSs present good correlations with storm tracks and jet streams, respectively. Moreover, RWs affect ETEs by two mechanisms. On one hand, RWE affects the occurrence rate of ETE, which increases with the amplification of RWE. On the other hand, under the condition of ETEs, RWPS affects the occurrence rate of persistent extreme temperature event (PETE), which increases with the decrease of RWPS. Due to the accompanied variations in the background states, the influence of RWE on the occurrence rate of ETE presents both seasonal and regional differences, while the influence of RWPS on the occurrence rate of PETE mainly demonstrates regional differences.