The Precipitation Structure of the Mediterranean Tropical-Like Cyclone Numa: Analysis of GPM Observations and Numerical Weather Prediction Model Simulations

Abstract

This study shows how satellite-based passive and active microwave (MW) sensors can be used in conjunction with high-resolution Numerical Weather Prediction (NWP) simulations to provide insights of the precipitation structure of the tropical-like cyclone (TLC) Numa, which occurred on 15-19 November 2017. The goal of the paper is to characterize and monitor the precipitation at the different stages of its evolution from development to TLC phase, throughout the storm transition over the Mediterranean Sea. Observations by the NASA/JAXA Global Precipitation Measurement Core Observatory (GPM-CO) and by the GPM constellation of MW radiometers are used, in conjunction with the Regional Atmospheric Modeling System (RAMS) simulations. The GPM-CO measurements are used to analyze the passive MW radiometric response to the microphysical structure of the storm, while the comparison between successive MW radiometer overpasses shows the evolution of Numa precipitation structure from its early development stage on the Ionian Sea into its TLC phase, as it persists over southern coast of Italy (Apulia region) for several hours. Measurements evidence stronger convective activity at the development phase compared to the TLC phase, when strengthening or weakening phases in the eye development, and the occurrence of warm rain processes in the areas surrounding the eye, are identified. The weak scattering and polarization signal at and above 89 GHz, the lack of scattering signal at 37 GHz, and the absence of electrical activity in correspondence of the rainbands during the TLC phase, indicate weak convection and the presence of supercooled cloud droplets at high levels. RAMS high-resolution simulations support what inferred from the observations, evidencing Numa TLC characteristics (closed circulation around a warm core, low vertical wind shear, intense surface winds, heavy precipitation), persisting for more than 24 h. Moreover, the implementation of DPR 3D reflectivity field in the RAMS data assimilation system shows a small (but non negligible) impact on the precipitation forecast over the sea up to a few hours after the DPR overpass.

The Role of Sea Surface Temperature Forcing in the Life-Cycle of Mediterranean Cyclones

“…MERRA-2 maximum values could be mainly found in the mainland of Greece and Italy in comparison with that of modeled and remote sensing that were also observed in the Adriatic Sea. The same result was evident in a relevant modeling study of cyclone Numa, also supported by radar data [37]. Concerning cyclone Zorbas, the accumulated precipitation fields derived from the satellite estimates tended to extreme rainfall values in the South Mediterranean (Figure 17).…”

“…Differences in the maximum values were evident in the range of 4 to 5 m/s and could be found in the cyclones Trixi and Zorbas. It should also be stated that maximum wind speed results in cyclone Numa are in good agreement with the ones presented in a similar study for the same event [37]. The resulting significant wave heights from the different runs were evaluated against the ones derived from JASON satellites.…”

“…The last hours of the same day, the storm started obtaining sub-tropical characteristics. During 17 November, when it was located in the Ionian Sea (Figure 4a), the storm presented tropical characteristics [37] that maintained until the next day ( Figure 4b). Moving eastward on 19 November, it dissipated over the Greek Peninsula.…”

Insights into the convective evolution of Mediterranean tropical‐like cyclones

“…Previous studies have shown that DC is weaker or shallower during and after the maximum intensity of some MTLCs (e.g. Claud et al, 2010;Miglietta et al, 2013;Cioni et al, 2016;Marra et al, 2019) but this statement was not confirmed for the majority of the selected MTLCs presented in this study. In addition, the DC during NUMA followed the diurnal solar cycle, probably due to the radiative cooling of the cloud tops, a process that increases instability in the troposphere (Wu and Ruan, 2016), but additional analysis has to be conducted to investigate this feature.…”

“…The first one between 1200 UTC 17 November and 0600 UTC 18 November 2017 was directly associated with an MCS in the upshear left quadrant which was detected by numerous DCPIXELS (Figure 9h) and COV for more than 12 hr when DLS was weaker or slightly stronger than 10 m⋅s −1 and the vortex tilt was less than 50 km (Figure 8h). Also during this period, the maximum intensity of the cyclone was estimated by ERA5 as for Marra et al (2019). The DC activity was clearly closer to the centre compared to the first 12 hr of the tracking, even though MWDC and COV were detected in the outer parts of the cyclone periphery (e.g.…”