Evaluating tropical upwelling variability and trends using GPS-RO and reanalyses

Abstract:

As the upward branch of the Brewer Dobson circulation, tropical stratospheric upwelling plays a vital role in tracer transport between tropical and extratropical stratosphere. Models and reanalyses both depict a strengthening of tropical upwelling over time. If this is true, it may indicate an acceleration of the Brewer Dobson circulation, and an increase in tracer transport from the tropical region to the poles. However, tropical upwelling cannot be observed directly, and the processes which control tropical upwelling occur at small vertical and horizontal scales, which are difficult to observe, making evaluation of simulated trends difficult. GPS-RO data from missions like COSMIC has an accuracy on par with radiosondes, and a vertical resolution higher than nadir-viewing sounders. With the advent of COSMIC 2, the number of soundings taken has increased from roughly 2,000 per day to 5,000 per day, especially the tropical atmosphere, allowing us to sample the temperature structure of the tropical upper-troposphere-lower-stratosphere in space and time, enabling us to better study the trend and variability of the tropical upwelling. Also, we know that tropical upwelling is mainly driven by extratropical waves as shown in previous studies. With higher resolution and better representation of resolved waves in ERA 5, we also plan to compare tropical upwelling as well as study the variability of tropical and extratropical waves and their potential influences on the tropical upwelling and tropical tropopause layer structure between ERA 5 and other reanalyses.