Research about diabatic tilting of potential vorticity
A schematic diagram illustrating changes in isentropic surfaces (black) and a vorticity tube (vorticity in green and velocity rings perpendicular to it in blue) that are (a) originally in parallel and have undergone (b) adiabatic tilting and (c) diabatic tilting
PV field describes the balanced part of atmospheric flow in weather systems. While convective clouds can change the balanced and unbalanced parts of the flow by diabatic heating or cooling, studying diabatic effects on PV is important because it untangles the changes in the balanced part of the flow from coupling with the unbalanced part. In the pioneering study on PV by Hoskins et al. (1985), they pointed out that diabatic heating or cooling changes PV mainly through diabatic streching for quasi-geostrophic balanced flow (small Rossby number), and then they dropped the diabatic tilting term in the PV equation. However, some later studies dropped the diabatic tilting term without considering the possibility of its importance given the large Rossby number, leaving me wondering.
This study reinterprets such a process as along-isentropic (horizontal) flux of PV due to cross-isentropic (vertical) momentum transport. Given vertically sheared winds, latent heat release in convective clouds tends to yield a pair of opposite signed potential vorticity (PV) without the need of preexisting PV.
This study gives insight into how convective clouds can change a weather system because, generally, the balanced part of the change stays in the weather system while the unbalanced part disperses with gravity waves. It explains how convective clouds can lead to inertial or symmetric instability because this process can change the sign of PV. Such insight may lead to improvement in weather prediction, which improves our lives.
Recorded Presentation at the 99th AMS Annual Meeting on 7 Jan 2019
My ongoing side project (2018-)
Ong, H. (2020). Comments on “On the Structure and Formation of UTLS PV Dipole/Jetlets in Tropical Cyclones by Convective Momentum Surges”. Mon. Weather Rev., 148(11), 4693–4695.