Diagnostic Analyses of Regional to Global Temperature Changes from Intraseasonal to Interdecadal Timescales
Open Access
- Author:
- Clark, Joseph
- Graduate Program:
- Meteorology and Atmospheric Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 12, 2021
- Committee Members:
- Eugene Clothiaux, Major Field Member
Sukyoung Lee, Major Field Member
Steven Feldstein, Chair & Dissertation Advisor
Andrew Carleton, Outside Unit & Field Member
David Stensrud, Program Head/Chair - Keywords:
- Climate Variability and Change
Atmospheric Dynamics
Teleconnections - Abstract:
- Despite the important societal impacts of surface air temperature (SAT) changes, the precise mechanisms that drive SAT changes remain an elusive subject of continuing research. Here, I investigate the drivers of SAT changes from intraseasonal to interdecadal timescales. On the intraseasonal timescale, I examine the SAT changes that occur when the winter North Atlantic Oscillation (NAO) and Pacific/North American (PNA) teleconnection patterns are active. On interdecadal timescales, I examine the long-term SAT trend, with particular attention to Arctic amplification (i.e., the amplified warming trend observed and simulated over the Arctic in response to anthropogenic greenhouse gases). On intraseasonal timescales, I conduct a thermodynamic energy budget for days when the NAO and PNA teleconnection patterns are active (i.e., when the positive or negative modes are strongly present). The budget reveals horizontal temperature advection as a dominant contributor to SAT anomaly growth, while SAT anomaly decay is caused mostly by longwave radiative heating. Important contributions to SAT anomaly growth or decay are also shown to come from vertical mixing (i.e., vertical turbulent eddy heat fluxes), especially for the PNA. These results highlight a necessity for correctly parameterizing vertical mixing and radiative heating. For interdecadal timescales, I conduct a Self-Organizing Map (SOM) analysis to reduce the dimensionality of the Arctic SAT anomaly dataset. I show that 9 recurring intraseasonal SOM patterns, driven by horizontal temperature advection, have interdecadal trends in their frequency of occurrence that can explain about half of Arctic amplification. I also examine interdecadal SAT trends through linear regression and find that Arctic amplification and the recent continental cooling trend may be linked to a recent trend toward enhanced La Niña-like tropical convection in the equatorial pacific. I close with a study investigating the drivers of the global interdecadal surface downward longwave irradiance (SDLI) trend, an important process contributing to interdecadal skin temperature (i.e., the temperature of the Earth’s surface) changes, using the Rapid Radiative Transfer Model. I decompose the global interdecadal SDLI trend into contributions from each variable on which it depends, showing that CO2 has directly contributed by a factor of ten more to recent SDLI trends than any other greenhouse gas. I also show that the greenhouse effect is strongest in places where the climatological water vapor concentration is low, and the climatological atmospheric temperature is high. Finally, the most important variables controlling SDLI changes are water vapor concentrations and atmospheric temperature changes. A diversity of processes contributing to temperature changes are examined in this dissertation on a range of spatial and timescales. Circulation changes are crucial for temperature anomaly growth on all of these timescales and atmospheric warming, caused by circulation changes, is communicated to the surface through changes in SDLI .