Observational and Modeling Study of Polar Middle Atmosphere Dynamics and Thermal Structures

• Main Author: Tan, Bo
• Format: Text
• Language: unknown
• Published: CU Scholar 2012
• Subjects: atmosphere dynamics; cold pole; inter-hemispheric coupling; lidar; teleconnection; temperature; Aerospace Engineering; Oceanography and Atmospheric Sciences and Meteorology; Remote Sensing; South Pole; Rothera; South pole
• Online Access: https://scholar.colorado.edu/asen_gradetds/52; https://scholar.colorado.edu/cgi/viewcontent.cgi?article=1052&context=asen_gradetds

A middle atmosphere temperature benchmark in the polar region is critical to monitoring the climate change. However, it is very challenging to establish such a benchmark because it is difficult to observe temperatures in the polar region and numerous factors affect the temperature variations. Ground-base lidars are capable of providing high-resolution and long-duration measurements of temperatures in the polar region, which is critical in advancing our understanding of the middle atmosphere thermal structures and dynamics. In this study, the lidar temperature morphology is formed at Rothera (67.5ºS, 68ºW) and South Pole using the lidar observations from 1999 to 2005. Teleconnection (inter-hemispheric coupling) is one of the new mechanisms causing, e.g., the temperature variations in the southern polar middle and upper atmosphere by regions not physically attached, e.g., the northern polar stratosphere. We study it by deriving the teleconnection patterns over the global latitudes and from the stratosphere to lower thermosphere using 8-year temperature observations of SABER and 54-year temperature and wind simulations of WACCM. A main new finding is that the teleconnection extends well into the lower thermosphere, the thermospheric anomalies are consistent with the corresponding changes of the winter-to-summer lower-thermospheric branch of the residual circulation, and the winter stratosphere perturbations influence the stratosphere, mesosphere and thermosphere globally. Cold pole bias is a long-standing problem in most general circulation and chemistry climate models, referring to the simulated southern winter stratosphere is significantly colder than observations. Our lidar measurements are used to quantify such bias in WACCM. We then propose a new inertial gravity wave (IGW) parameterization to compensate the missing wave drag in WACCM, with which the simulated temperature is increased by 20 K and the simulated zonal wind jet is decreased by 10−30 m/s in the southern winter stratosphere. Also, the polar vortex breaks earlier and the wind reversal level during spring is lower, making the WACCM simulations closer to observations. Overall this thesis work helps advance our understanding of the polar region thermal structure and how dynamics affect the temperature variations. It lays the foundation to establish the temperature benchmark for studies of climate change.