Climate dynamics

Dynamics of the Madden-Julian Oscillation (MJO):


The MJO is a slow moving (20-60 day) planetary-scale weather pattern in the tropics, whose underlying dynamics and climate sensitivity remain in debate. My past work on its fundamental dynamics had focused on the role of lateral vapor advection in its eastward propagation [11]. While at UCI I have designed new SP experiments that further assess the role of storm-scale convective organization in MJO dynamics [14] as well as idealized aquaplanet sensitivity tests that exposed the SP-MJO to a wide range of thermal conditions in the exotic condition of uniform global temperatures for hypothesis stress testing [22]. Results from these experiments have supported some aspects of the “moisture mode” view of the MJO, while also challenging a modern theory for a temperature sensitivity in the role of radiative convective instability that is widely thought to destabilize it. Along the way I have contributed model output and analysis of simulations to community efforts that have attempted to clarify the realism of the MJO and current issues associated with trying to simulate it [15,16-17]. I remain interested in the potential for the MJO to amplify in future climate and my third PhD student, M. Fowler, is currently analyzing the ramifications of MJO amplification for regional tropical cyclone genesis and streamflow anomalies. MJO-tropical cyclone interactions: Recently, with a PhD student, in Fowler and Pritchard (2020), I branched out to consider impacts of the MJO on tropical cyclone activity in the West Pacific, relying mostly on observations. We used quasi-explicit empirical TC downscaling tools developed at MIT to sidestep traditional sample size limitations. The results reveal a region of the South China Sea that is especially prone to MJO-induced tropical cyclone genesis. This is relevant to understanding how humans may be impacted by changing TC statistics as the MJO amplifies with climate warming and its convective envelope spreads farther into the Pacific Ocean.

MJO-tropical cyclone interactions:


Recently, with a PhD student, in Fowler and Pritchard (2020), I branched out to consider impacts of the MJO on tropical cyclone activity in the West Pacific, relying mostly on observations. We used quasi-explicit empirical TC downscaling tools developed at MIT to sidestep traditional sample size limitations. The results reveal a region of the South China Sea that is especially prone to MJO-induced tropical cyclone genesis. This is relevant to understanding how humans may be impacted by changing TC statistics as the MJO amplifies with climate warming and its convective envelope spreads farther into the Pacific Ocean.

Planetary scale coupled climate energetics:


Since 2018 I branched into a new topic of global-scale ocean-coupled energy transport dynamics. In Yu and Pritchard (2019), together with my first PhD student, we designed a new form of climate model experiment that has not been tried before in which opposing hemispheres are intentionally subject to dimmed vs. brightened sunlight in annular forcing rings that can be moved closer or farther from the equator. The results (Yu and Pritchard 2019) highlighted a profound role for the Atlantic Meridional Overturning Circulation (AMOC) to overwhelm atmospheric degrees of freedom that might otherwise mediate the energy imbalance in association with shifting rainfall bands. The bottom line is that robust theories of forced shifts in the location of the ITCZ rainband – of interest to billions of humans adapted to its current location – are entangled with challenging AMOC dynamics. Beyond the above student-led activities I collaborate on modern climate dynamics topics of radiative convective self-aggregation (Beucler et al. 2019).


Contact

164 Rowland Hall
University of California, Irvine
Irvine, CA 92697-4675