PRODUCT NAME: PR-OBS-03v1.2
CASE STUDY PERIOD:
13 Jan 2009 00:12 to 23:57 UTC
VALIDATION INSTITUTE:
University of Ferrara
PRODUCT DEVELOPER INSTITUTE:
CNR- ISAC
OPERATIONAL CHAIN INSTITUTE:
CNMCA
METEOROLOGICAL EVENT:
Large deep cloud system over southern Italy
Responsible:
Porcù F.
Contact point: porcu@fe.infn.it
Developers:
Laviola S., Cattani E.
Responsables:
Zauli F
METEOROLOGICAL EVENT DESCRIPTION
Contact point: s.laviola@isac.cnr.it
Contact point: zauli@meteoam.it
On January 12-13 a deep low pressure structure established over north Africa. The instability in southern Mediterranean makes the whole area prone to convective development. The strong high pressure over Turkey makes slower the eastward motion of the low, causing a blocking situation.
SEVIRI IR image at 06:00 (on Jan
13) shows a huge cloud shield covering southern Italy and surrounding areas. It was formed from merging of long lasting structures moving from the south in the previous day. The cloud top is very cold, attesting embedded convection, that can also be triggered by orography over Sicily and southern Italy. The IR is not able to show the structure of the cloud system.
DATA/PRODUCTS USED

Reference data: Italian hourly raingauges network (provided by DPC)
Ancillary data (used for case analysis):
SEVIRI images (courtesy of University of Dundee – NEODAAS)
Weather charts (courtesy of Wetterzentrale)
RESULTS OF COMPARISON
The main features of this product is, if compared to h01 and h02, is the capability of providing a continuous monitoring of the full area of interest every 15 minutes, at a much higher ground resolution.
We considered for this case one full day of observation, and compared the gauges hourly cumulated rainfall with the average of the satellite estimates in the four slots in the given hour, at 12 th
, 27 th
, 42 th and 57 th
minutes.
This event can be divided in two parts: in the first half of the day convective precipitation was found over Sicily and Calabria, while in the afternoon more stratified and moderate rainfall reached also central Italy.
These two phases were also differently described by the h03 maps. The first (convective) part was fairly good understood, with averaged POD around 0.6 and a rather low FAR (0.2), with corresponding
ETS ranging between 0.22 and 0.57. The corresponding HSS show values between 0.16 and 0.35, indicating acceptable skill in detecting high precipitation areas, even if the estimate is markedly lower than the measure.
For the second part of the event, the performances strongly decrease, showing average POD and FAR of about 0.2 and 0.35, respectively, while ETS and HSS show values of few cents above the no-skill value (zero for both indicators).
A clear picture of this different behaviour is given by the figures below: in the top panels estimates
(left) and raingauges (right) precipitation from 03:00 to 04:00 UTC are shown, while in the bottom panels the same is presented for the 18:00-19:00 hour. The top panel shows the best performances and the bottom panel the worse for the whole event.
Even for the best matching, however, the estimation technique show its main weakness, largely overestimating the precipitation area over southern Italy. The precipitation over Sicily is also partially overestimated, while smaller area over Sardinia are detected, but a little misplaced. The estimated rainrates are very low and is not well represented the structure of the precipitation fields in terms of intensity over Calabria, while over Sicily, more precipitation is correctly estimated on the eastern part of the Island rather on the western one, in qualitative agreement with raingauges.
The figures in the bottom panels show that, for the second part of the event, some underestimation of precipitating areas is also significant: no precipitation is estimated over Sicily and Sardinia, while a large false alarm area is present over central Italy.

Figure. Top panel: h03 averaged precipitation map between 03:12 and 3:57 UTC (left) and raingauges hourly precipitation cumulated at 04:00 UTC (right) of 13 January 2009. Bottom panel: h03 averaged precipitation map between 18:12 and 19:57 UTC (left) and raingauges hourly precipitation cumulated at 19:00 UTC (right) of 13 January 2009. Please note different colour scales for estimates and measure.
COMMENTS
This event was characterized by both convective and stratified precipitation, and h03 performed differently for the two regimes. The calibrating passive microwave estimate is effective in detecting and resolving convective structures, and errors are mainly due to the IR. For stratified precipitation, very likely the quality of the microwave calibration is lower, and this results in worse performance of the technique, given the weak relation between IR radiance and precipitation at the ground.
Indications to Developers
Improvement of this technique have to go in two directions: to choose the best possible microwave

estimate, and improve the IR contribution. For the first issue, it has to be considered that different microwave algorithms perform differently, with different pros and cons, depending on cloud system, precipitation type, geographical area, background. The IR could take benefit from the multispectral capability of the last generation of geostationary satellite sensors.