Assessing the impact of SSTs on a simulated medicane using ensemble simulations

Abstract

Abstract. The sensitivity of the October 1996 medicane in the western Mediterranean basin to sea surface temperatures (SSTs) is investigated via 24-member ensembles of regional climate model simulations. Eleven ensembles are created by uniformly changing SSTs in a range of −4 K to +6 K from the observed field, with a 1 K step. By using a modified phase space diagram and a simple compositing method, it is shown that the SST state has a minor influence on the tracks of the cyclones, but a strong influence on their intensities. Increased SSTs lead to greater probabilities of tropical transitions, to stronger low- and upper-level warm cores, and to lower pressure minima. The tropical transition occurs sooner and lasts longer, which enables a greater number of transitioning cyclones to survive landfall over Sardinia and to re-intensify in the Tyrrhenian Sea. The results demonstrate that SSTs influence the intensity of fluxes from the sea, which leads to greater convective activity before the storms reach their maturity. These results suggest that the processes at steady-state for medicanes are very similar to tropical cyclones.

Large-scale secondary circulations in a limited area model – the impact of lateral boundaries and resolution

“…That the use of domain shifting techniques is a valuable tool for estimating uncertainties in RCM ensemble simulations, has been shown in several studies (e.g. Pardowitz et al, 2016;Mazza et al, 2017;Noyelle et al, 2018).…”

Subtropical Cyclone Anita's Potential to Tropical Transition Under Warmer Sea Surface Temperature Scenarios

“…Thus, the cyclone can be self‐sustaining, as delineated in the following: (a) Deep convection contributes to the decrease of the cyclone central pressure once air is transported from the lower to the upper levels; (b) a lower central pressure minimum implies stronger pressure gradients with the neighboring areas and, consequently, more intense low level winds; (c) stronger winds increase the turbulent heat fluxes from the sea to the atmosphere (and, consequently, increase evaporation; Zeng et al, ); and (d) the chain of physical processes continues (feedback mechanism): With a more intense cyclone, the sea‐air fluxes increase, and the system continues to strengthen. This sequence of processes is known as WISHE theory for tropical cyclone development (Emanuel, , ), and the same processes explain the intensification of tropical‐like cyclones in the Mediterranean Sea (Cioni et al, ; Miglietta et al, , ; Miglietta & Rotunno, ; Noyelle et al, ; Tous & Romero, ). In the present study, part of the a–d sequence of processes can be observed in Figures b and c.…”

“…Following Gozzo et al (), over the SAO, a cyclone can be classified as subtropical when B < 25, −V T L > −50, and −V T U < −10. As pointed out by Noyelle et al (), the B parameter is sensitive to the exact location of the cyclone center (i.e., it captures the local information), while −V T U on its own is more suitable to capture the cyclone environment. Hart's algorithm to compute the CPS requires the track of the cyclone and the geopotential height at three pressure levels (900, 600, and 300 hPa).…”

“…These systems occur in different ocean basins as well as in the South Atlantic Ocean (SAO; da Rocha et al, ). Numerical sensitivity experiments have shown that the turbulent heat fluxes at the sea‐air interface are important to sustain the convection and, consequently, to strengthen the structure of the subtropical cyclones (Noyelle et al, ; Miglietta et al, ; Miglietta & Rotunno, ; Pytharoulis, ; Tous & Romero, ).…”

Cell tracking of convective rainfall: sensitivity of climate-change signal to tracking algorithm and cell definition (Cell-TAO v1.0)

“…An ensemble is then created using the domain-shift technique (e.g. Rezacova et al, 2009;Pardowitz et al, 2016;Noyelle et al, 2018). In this approach, a central domain is defined and the domain centre is systematically shifted five grid cells (∼0.55 • ) in the cardinal and ordinal directions N, NE, E, SE, S, SW, W and NW, giving perturbed initial and boundary conditions for each ensemble member (see Rezacova et al (2009) and Mazza et al (2017) for illustrative schematics).…”