Diagnosis of the Sensitivity of Type B Cyclones to the Structure and Evolution of Their Upper-Tropospheric Precursors

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

Mid-latitude surface cyclones, the familiar "low-pressure systems" seen on surface weather maps, are significant organizers and producers of precipitation, strong winds, and rapid changes in temperature. The development and subsequent intensification of these surface cyclones (cyclogenesis) is often preceded by the development of a disturbance 9-13 kilometers above the surface (i.e., the upper-troposphere and lower-stratosphere). Studies of cyclogenesis have revealed two stages: First, development of an upper-tropospheric front and associated extrusion of stratospheric air into the upper and mid-troposphere associated with wind shear in cyclogenesis. Second, a period of development during which shear is converted to curvature in cyclogenesis. It has been shown that processes of extrusion of stratospheric air into the upper-troposphere and the subsequent conversion of these two steps are not only important in configuring the upper-trough for subsequent cyclogenesis, but also in shaping the subsequent intensification rate of the cyclone. It is unclear how these processes synergistically interact or what individual importance each of these processes assumes in cyclogenesis. This project will explore how small changes to the initial conditions of simulated upper-tropospheric cyclone precursors impacts the evolution of the surface cyclone. The results of this proposed project will provide insight into the timing and location of critical processes occurring in the upper-troposphere prior to cyclogenesis and potentially offer insight into improvements in reducing the uncertainty associated with predictions of the intensity of these weather events. The fundamental research conducted in this project is consistent with NSF's mission of promoting the progress of science. The broader impacts of the proposed activity include the training of graduate students, the organization and hosting of a workshop to explore the predictability of cyclones and their lifecycles, and the organization of a session on mid-latitude lifecycles at the 2022 annual meeting of the American Meteorological Society. This study proposes to investigate the dynamics of midlatitude cyclogenesis events by addressing the sensitivity of extratropical cyclone development to the evolution of the upper tropospheric cyclogenetic precursor (UTCP) within the framework of case studies of simulated observed cyclogenesis events. The project combines two well-developed diagnostic techniques (i.e., quasi-geostrophic (QG) diagnostics and adjoint-derived forecast sensitivities) to understand an outstanding issue related to mid-latitude cyclogenesis: the sensitivity of the Type-B cyclone lifecycles to perturbations to the cyclones' upper-tropospheric cyclogenetic precursors. The unique combination of the diagnostic approaches allows for previously unexplored research into understanding the separate and interactive roles of upper-tropospheric, pre-cyclogenetic, barotropic and baroclinic growth processes in modulating surface cyclone lifecycles. We will use a novel experimental approach termed the sensitivity-perturbation-response-diagnosis (SPRD) procedure. SPRD employs adjoint-derived sensitivity gradients for individual cases to construct optimal perturbations that elicit particular, prescribed responses in the simulated cyclone life cycle for which synoptic-scale QG and potential vorticity (PV) inversion diagnostics of the perturbed cyclone evolutions are performed. Employment of this procedure will result in a comprehensive examination of the structure and evolution of optimal initial-time perturbations influencing the cyclone's development, as well as a test of the appropriateness of the simplifying assumptions in the adjoint model to each particular case. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.