Sante Laviola

Detection and Measurement of Snowfall from Space

Snowfall detection and measurement represent highly difficult problems in modern hydrometeorology. Ground measurements are complicated due to detection technology limitations, snow drift and accumulation issues, and error definition. The snowfall detection from space is in turn affected by all detection limitations that characterize the measurement of rainfall with the addition of several complications, such as the indirect character of remote sensing precipitation estimation, the presence of frozen or snow-covered terrain, and the unknown vertical distribution of hydrometeors in the cloud column. Several methods for the retrieval of snowfall intensity from satellite have been proposed in recent times using passive and active sensors. No satisfactory answer to the general problem of quantitative snowfall intensity determination has been found to date, but several studies contribute to delineate a working framework for the future operational retrieval algorithms.

Satellite and Numerical Model Investigation of Two Heavy Rain Events over the Central Mediterranean

AbstractTwo heavy rain events over the Central Mediterranean basin, which are markedly different by genesis, dimensions, duration, and intensity, are analyzed. Given the relative low frequency of this type of severe storms in the area, a synoptic analysis describing their development is included. A multispectral analysis based on geostationary multifrequency satellite images is applied to identify cloud type, hydrometeor phase, and cloud vertical extension. Precipitation intensity is retrieved from (i) surface rain gauges, (ii) satellite data, and (iii) numerical model simulations. The satellite precipitation retrieval algorithm 183-Water vapor Strong Lines (183-WSL) is used to retrieve rain rates and cloud hydrometeor type, classify stratiform and convective rainfall, and identify liquid water clouds and snow cover from the Advanced Microwave Sounding Unit-B (AMSU-B) sensor data. Rainfall intensity is also simulated with the Weather Research and Forecasting (WRF) numerical model over two nested domains w...

Rain retrieval using the 183 GHz absorption lines

High spatial resolution AMSU opaque channels are used to retrieve rain rates and classify precipitation types. The retrieval scheme (183-WSL) consists of two fast algorithms, one for land and the other for sea surface, that use the water strong lines at 183.31 GHz to infer rain rate amounts based on a series of thresholds calculated to remove the condensed water vapor effect and discriminate between convective and stratiform pixels. The reported results show the sensitivity of the technique to detect deep convective clouds and to measure light-rain stratiform systems. This latter fact recommends its application particularly over mid-latitude basins where persistent light rains cause intense run-off episodes. Other studies are planned to apply the method at high latitudes where the atmospheric humidity is mainly located within the surface layers and appropriate correction coefficients need to be found.

Quantitative Precipitation Estimation from Earth Observation Satellites

Rainfall: State of Geophysical Mon Copyright 2010 b 10.1029/2009GM The observation of the atmosphere by satellite instrumentation was one of the first uses of remotely sensed data nearly 50 years ago. Satellites offer an unrivalled vantage point to observe and measure Earth system processes and parameters. Observations of meteorological phenomena permit a more holistic view of the weather and climate that is not possible through conventional surface observations. Precipitation (rain and snow), in particular, benefit from such observations, since precipitation is spatially and temporally highly variable and overcome some of the deficiencies of conventional gauge and radar measurements. This paper provides an overall review of quantitative precipitation estimation, covering the basis of the satellite systems used in the observation of precipitation and the dissemination of this data, the processing of these measurements to generate the rainfall estimates, and the availability, verification, and validation of these precipitation estimates.

Potential vorticity patterns in Mediterranean “hurricanes”

The potential vorticity (PV) anomalies due to the intrusion of dry stratospheric air and those generated by the tropospheric diabatic latent heating are qualitatively analyzed for five Mediterranean tropical-like cyclones (also known as Medicanes or TLCs). Model simulations show the presence of an upper level PV streamer in the early stages of the cyclone, located on the left exit of a jet stream, and a middle-low level PV anomaly generated by the convection developing around the low-level vortex. In the mature stage, the upper level PV anomaly around the cyclone evolves differently for each case and appears somehow dependent on the lifetime. Only for the 2006 Medicane, the PV anomalies form an intense PV tower extending continuously from the upper troposphere to the lower stratosphere.

Extreme precipitation on the Island of Madeira on 20 February 2010 as seen by satellite passive microwave sounders

Abstract Extreme rainfall on the Island of Madeira on 20 February 2010 triggered flash floods and mudslides with 45 casualties, 8 missing people, and 100 injured. The NE-moving frontal system originating from a low-pressure center in the Madeira Archipelago is not unusual for the area, but its consequences on the island were rather extreme. The study dwells on passive microwave sounders from polar orbiters for the retrieval of rainfall intensity and cloud classification. Heavy rainfall was generated by severe local convection and enhanced over the central mountain chain. Physical cloud classification identifies the shallow convective precipitation type lasting for a few hours around noon and the observations confirm the numerical model results.

An intercomparison of two passive microwave algorithms for snowfall detection over Europe

The proposed work aims to enhance the capabilities of the passive microwave measurements on board NOAA and MetOp satellites for snowfall identification. Two independent methods based on the same sensors (AMSU/MHS) were applied and qualitatively inter-compared during snowstorms over Europe by using the NIMROD radar network as ground truth. The first method developed at NOAA is a statistical algorithm that computes the probability of snowfall using a logistic regression and the principal components of the high frequency brightness temperature measurements at MHS or ATMS channel frequencies 89 GHz and above. The second approach for snowfall detection (183-WSLSF) developed by CNR-ISAC is a prototype based on the preexistent 183-WSL retrieval method. By considering as limit of snowfall formation the rainy clouds located from a few hundred meters to 5-6 km, the 183-WSLSF combines channel sensitivities from 90 and 190 GHz to identify snowfall areas in the precipitating cores.

Passive Microwave Remote Sensing of Rain from Satellite Sensors

The purpose of this chapter is to offer an accurate treatment of relevant aspects of satellite remote sensing of precipitation using passive microwave (PMW) radiometers. Microwave observations of the Earth’s system differ substantially from those based on optical and infrared wavelengths. Visible (VIS) and infrared (IR) instruments essentially sense the cloud top properties by measuring reflected or emitted radiation. Microwave frequencies, on the contrary, possess greater penetrating capabilities than optical radiation and can thus be exploited to investigate cloud internal properties by retrieving the interaction of hydrometeors with the radiation field. This fact is particularly true in the remote sensing of precipitation, where the impact of the volume of raindrops on the radiative field is directly linked to the total extinction of incident radiation. The following paragraphs will be focused on one hand on theoretical considerations at the foundations of thermal radiation processes and on the other the attention will be centered on a treatment of practical aspects of retrieving precipitation in the microwave bands. Particular attention will be dedicated in the first part of the chapter to the radiative transfer theory in the microwaves by using the Rayleigh-Jeans formulation and a description of the absorption and scattering processes associated with the Mie theory with the approximation of extinction from poly-disperse media as proxies for natural media. This section will create a valid substrate to understand and theoretically evaluate the impact of atmospheric constituents such as precipitation types or hydrometeor phases and sizes on the natural radiation emitted from the Earth. Furthermore, the theoretical considerations of this section will be compared in the second part of the chapter with real measurements. Making use of a wide suite of microwave frequencies of a new generation of PMW sensors flying on board polar orbiting satellites the attenuation of the microwave signal due to rain clouds will be discussed possibly discerning the contribution to the total radiation of the emissivity from various surfaces falling into the satellite field of view. Finally, a new microwave highfrequency method to retrieve and classify precipitation types will be presented.