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.
Highlights
The Mediterranean Sea is recognized as a climatic hotspot [1], often affected by severe weather events that are becoming more and more frequent in the last decades
In the first part of this study we describe the evolution of Numa, from its formation to its dissipation, by using a “traditional” approach suitable for Near Real Time (NRT) applications, i.e., based on visible (VIS) observations, environmental conditions provided by the European Centre for Medium-Range Weather Forecasts (ECMWF), and lightning activity associated with the storm, as measured by the LIghtning NETwork (LINET) [29]
The analysis carried out for Medicane Numa highlights how powerful MW radiometers are in identifying the details of its precipitation structure, not discernible in conventional (VIS or IR) satellite imagery, as it evolves over the Mediterranean Sea
Summary
The Mediterranean Sea is recognized as a climatic hotspot [1], often affected by severe weather events that are becoming more and more frequent in the last decades Among these events, increasing attention has been recently devoted to the so-called Mediterranean hurricanes (Medicanes) or tropical-like cyclones (TLCs). TLCs have a typical diameter of 100–300 km, while the associated surface wind speed can occasionally reach 22–28 ms−1 They are characterized by the presence of a quasi-cloud-free calm eye, strong winds close to the vortex center, spiral-like cloud bands elongated from the center, vertical alignment of pressure minima, weak vertical wind shear, and a warm anomaly [2,3,4,5,6,7,8,9,10,11,12]. These cyclones may last for several days, the presence of tropical characteristics is generally limited to a few hours
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