Extratropical Control of Gulf Surges: The Role of Rossby Wave Breaking and Associated Mesoscale Processes

Affiliation(s)PIProject periodFunded by
DAS Kaplan, Michael L. 05/01/2008 - 04/30/2011 National Science Foundation

Project Description

Our stated hypothesis: RWB and the subsequent amplification of the upper-level monsoonal ridge set the stage for gulf surges through the following steps: (a)RWB leads to an abrupt poleward shift in the jet, a relaxation of QG-forcing over the interior western US, and a northeast shift in the monsoon ridge. These processes collectively act to provide an opening for mesoscale forcing to dominate. (b)Filaments of extratropical air following RWB are deposited into the subtropics and form a TUTT that wraps anticyclonically around the monsoonal high towards the GOC. (c)Dramatic heating over the Great Basin and an elevated PBL lead to a drop in surface pressure thereby funneling moist air over the GOC ahead of the TUTT northward to create a gulf surge. This hypothesis is based on observations and a preliminary investigation. However to solidify our hypothesis we plan to examine both observations coinciding with the NAME 2004 period as well as test our hypothesis in a set of numerical model simulations. The following is a list of objectives needed to satisfy our hypothesis: 4.1 To diagnose the link between the RWB, the amplification of Rossby waves over the North American continent, and the presence of gulf surges. Emphasis will be placed on (1) influence of wave amplification and breaking on the movement of the monsoonal ridge, (2) influence of RWB on dampening QG-forcing over the interior western US, and (3) mechanisms for TUTT formation in the subtropics arising following RWB trough thinning. 4.2 To understand how the relaxation of QG-forcing over the interior western US coupled with pronounced ridging promotes widespread heating of the PBL over the Great Basin. Differential heating over the PBL effectively modulates the low-level surface pressure field is a manner needed to drive the TUTT over the GOC northward to create a gulf surge. 4.3 To understand the importance of the extratropical circulation in setting the stage for gulf surges. This objective will be examined in a modeling study to test the relative importance of the extratropics versus the tropics in providing conditions necessary for a gulf surge. 4.4 To validate and better understand the implications of these simulations employing NAME 2004 field observations.