Warm Core and Deep Convection in Medicanes: A Passive Microwave-Based Investigation

Abstract

Mediterranean hurricanes (Medicanes) are characterized by the presence of a quasi-cloud-free calm eye, spiral-like cloud bands, and strong winds around the vortex center. Typically, they reach a tropical-like cyclone (TLC) phase characterized by an axisymmetric warm core without frontal structures. Yet, some of them are not fully symmetrical, have a shallow warm-core structure, and a weak frontal activity. Finding a clear definition and potential classification of Medicanes based on their initiation and intensification processes, understanding the role of convection, and identifying the evolution to a TLC phase are all current research topics. In this study, passive microwave (PMW) measurements and products are used to characterize warm core (WC) and deep convection (DC) for six Medicanes that occurred between 2014 and 2021. A well-established methodology for tropical cyclones, based on PMW temperature sounding channels, is used to identify the WC while PMW diagnostic tools and products (e.g., cloud-top height (CTH) and ice water path (IWP)), combined with lightning data, are used for DC detection and characterization. The application of this methodology to Medicanes highlights the possibility to describe their WC depth, intensity, and symmetry and to identify the cyclone center. We also analyze to what extent the occurrence and characteristics of the WC are related to the Medicane’s intensity and DC development. The results show that Medicanes reaching full TLC phase are associated with deep and symmetric WCs, and that asymmetric DC features in the proximity of the center, and in higher CTH and IWP values, with scarce lighting activity. Medicanes that never develop to a fully TLC structure are associated with a shallower WC, weaker and more sparse DC activity, and lower CTHs and IWP values. Ultimately, this study illustrates the potential of PMW radiometry in providing insights into dynamic and thermodynamic processes associated with Medicanes’ WC characteristics and evolution to TLCs, thus contributing to the ongoing discussion about Medicanes’ definition.

Helios and Juliette: Two Falsely Acclaimed Medicanes

“…6 shows the TB anomaly for channels 6-8 of ATMS NPP overpass on 10 February at 12:07 UTC. At first sight, the warm TB anomaly could be associated with a deep WC structure observed in other medicanes, as illustrated in Panegrossi et al (2023). From a closer inspection, however, some remarkable differences can be noticed.…”

“…5f-h), a warm TB anomaly at mid/uppertroposphere levels (around 600, 400 and 300 hPa) is also present, as highlighted by channels 5-7 and 6-8 for AMSU-A and ATMS, respectively (not shown). The TB anomaly is calculated according to the methodology developed for tropical cyclones (Brueske and Velden, 2003; Velden and Herndon, 2020) and recently applied to medicanes (Panegrossi et al, 2023). In their work, Panegrossi et al ( 2023) defined a WC as very shallow if the warm TB anomaly is visible only in channel 6 (7) (peaking around 400 hPa), shallow if it is visible in channels 6(7) and 7(8) (peaking around 300 hPa), and deep if it is visible in channels 6(7), 7(8), and 8(9) (peaking around 200 hPa) from AMSU(ATMS) measurements.…”

“…for WC detection in Tropical Cyclones (Brueske and Velden, 2003), has been applied to medicanes (Panegrossi et al, 2023). Starting from PMW diagnostics for DC, ice water path (IWP) and cloud-top height (CTH) (Rysman et al, 2021), the authors highlighted the large variability, but also some possible clustering, of both thermodynamic and microphysics structures characterizing several medicanes.…”

“…Our work aims to provide a comprehensive description of Helios and Juliette mainly from an observational point of view, in order to compare them with other well-documented cyclones. More specifically, the PMW WC detection technique (Brueske and Velden, 2003;Panegrossi et al, 2023) is used to study the evolution of WC development in Helios and Juliette. In addition, high-frequency PMW channels are used to detect DC and estimate the CTH and IWP, as well as precipitation and cloud property diagnostics are utilized throughout the cyclones' development.…”

A New Refinement of Mediterranean Tropical‐Like Cyclones Characteristics

“…These cyclones are frequently called medicanes (MEDIterranean hurriCANES; Emanuel, 2005) or tropical-like cyclones (TLCs). These cyclones are characterized by the presence of deep warm core originated by intense convection in the mature stage (infrared channels and passive microwave sensors; Panegrossi et al, 2023;D'Adderio et al, 2024), and could be detected by satellite images because of their symmetrical structure and the presence of a cloud-free region in their center (visible channels). TLCs can drive important socio-economic losses in coastal areas as a result of intense precipitation, strong winds or storm surges.…”