Large Scale Dynamics and Tropopause Temperature
What controls the interannual variability of tropopause temperature? This project looks at the large scale dynamics that determine how cold the coldest point in the lower earth system gets on a year to year time scale. The tropics are dominated by the Quasi-biennial Oscilation (QBO) and the Brewer-Dobson Circulation (BDC). As we move poleward, the BDC becomes the primary mode of variability. Interestingly, this is true not only for the Cold Point Temperature (CPT) but also for the Lapse Rate Tropopause (LRT) temperature.
Covariability of Cold Point Temperature and Cirrus Cloud Fraction in Tropics
In the Tropical Tropopause Layer (TTL), cirrus cloud fraction (CF) and the cold point temperature are very well correlated on an interannual time scale (correlation coefficient = 0.62). Using a statistical technique called Maximum Covariance Analysis (MCA) we can intentify the primary modes controlling the covariability between cirrus CF and CPT. We then construct a Multiple Linear Regression (MLR) model using the El Nino Southern Oscillation (ENSO), the Madden-Julian Oscillation (MJO), the Brewer-Dobson Circulation (BDC) and the Quasi-biennial Oscillation (QBO) to partition the amounts of explained variance from each dynamical mode to identify which are most important to controlling the covariability. We find ENSO, the QBO and the BDC are all important in controlling the covaraibility between CF and CPT.
Diurnal Cycle of the Tropical Tropopause Layer
How does the TTL change on a daily basis? Now, armed with 14 years of COSMIC radio occultation data we can begin to ask question about the diurnal cycle in the TTL. From the figure on the left, we see that the TTL (70-150 hPa) has muted amplitudes of the diurnal cycle. Although these amplitudes are small, they are critical to understanding the amount of Stratosphere-Troposphere Exchange (STE) happening in the tropics. We have found that although the general characteristics of stratospheric and tropospheric diurnal cycles are captured in model and reanalysis data, key parts of the TTL, such as the 100 hPa contour (frequently taken as a proxy for the CPT), do not show similar diurnal cycles when compared to the radio occultation dataset. The reasons for this discrepancy are unknown and to our knowledge have not been investigated.
Hi! I am a second year grad student at the University of Washington studying Atmospheric Science. I focus on understanding phsyical processes in our atmosphere with the overall goal of helping humanity prepare for global climate change. I graduated from Florida State University with a BS in Physics & Astrophysics. Here at the UW, I work in the UW OUTREACH program, and am an ARCS Fellow.
I am advised by Qiang Fu.
My email is aodhan at uw dot edu
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