Friday, February 22nd 2013, 10:24 AM EST
I have had a look around at some unusual weather news reports from yesterday to see if I could locate a "Storm Enhancement" as per the Tropical Storm "power up" blog for Cyclone Haruna. The following report from Italy has all the ticks in right box's as far as I'm concerned....no doubt this event will be mistaken as an act of "man made" climate change, but it looks like a typical storm enhancement through a burst of solar activity.
Catania storm: a "dry intrusion" from the stratosphere and an intense "Wind Shear" among the causes of the violent storm that flooded the town of Etna by Daniel Ingemi, MeteoWeb.eu
Yesterday afternoon, a violent storm, characterized by electrical activity and very high indices of rain / rate has hit the city of Catania and its hinterland, at the foot of the eastern slopes of Etna. In less than an hour and a half strong backhand storm, assuming the guise of a genuine monsoon precipitation, was able to download about 60-70 mm of water, with peaks of more than 80-90 mm in internal areas and along the eastern slopes of Etna. On all stands the figure of Pedara which recorded an accumulation of more than 106 mm. It is, in fact, of very considerable accumulation in relation to the very short time.
All that water, falling in such a short time, could not be disposed of properly by the sewer system. This has resulted in extensive flooding, turning the main streets of Palermo in real streams in flood dragged parked cars, scooters and mopeds. The same central square in front of the cathedral, became a big swamp. From a purely synoptic eastern Sicily was expected worsening of weather conditions for the return of the old "CUT-OFF" (closed cyclonic vortex at the top) North African, away to the Ionian Sea. This would have led to a further destabilization atmospheric (reinforcing the "vertical thermal gradient"), fueled by the presence of moist currents from E-NE and NE, in the lower layers, which have helped to amass a very low cloud cover along the windward slopes of Etna and Peloritani south.
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This depression in share was preceded by an extensive "Warm Conveyor Belt", type "forward", well fed by the intense ascending branch of the "polar jet" that went along the eastern edge of the "CUT-OFF" North Africa, with maximum speed ("Jet Streak") statements over the Ionian Sea, where we witnessed a considerable increase in the "Vertical Wind Shear." But good for analyzing the evolution of the synoptic, between 15:00 and 19:00 UTC on Thursday, February 21, is known as the powerful "Cluster storm", characterized by violent "updrafts" (strong upward motions in the cloud Storm), who came to develop near the coastal area of Catania, between the eastern side of the southern and Peloritani (whose effect "springboard" to humid currents from the E-NE in the lower layers has certainly influenced the outbreak of strong turbulence that have produced the immense cumulonimbus), is not attributable to the classical situation of instability with a very strong "vertical thermal gradient" (large temperature differences within the column of air that becomes increasingly cold as they salt level). Or at least, the "thermal gradient", both horizontal (given the advection of warm air action in the Ionian Sea) and the vertical (with the influx of colder air masses at high altitude above the flow mild pre- front cover), in this case it was not the determining factor that favored the genesis of the convective system. Looking at the satellite images of water vapor note "fault" tropospheric that sparked the violent storm of Catania.
The factor that has triggered the development of this big thundercloud, between the coast of Catania and Messina ion between Etna and Peloritani, is a "dry intrusion" by the intrusion of very dry air of stratospheric origin in the upper troposphere that produced an intense "vertical humidity gradient" between the cold and dry air at high altitude in sliding over the very humid air masses (close to saturation) and temperate in action in the lower layers, on the windward side (the eastern side) of Etna and Peloritani. The phenomenon studied in synoptic meteorology (in Europe and the USA), is also known by the term "invasions stratospheric." In fact, the tropopause (ie the slice of atmosphere, high more than 12-13 km depending on the latitude, within which you can extend the vertical atmospheric motions) is not fixed, as erroneously thought, but in constant motion. This means that it is up and down all the time, depending on which hand you cold air of polar origin (which lowers the troposphere) or warm sub-tropical (which raises the troposphere). The undulations of the tropopause cause two different types of anomalies that can be positive or negative.
We speak of positive anomalies when "stratospheric air" invades the highest part of the troposphere, by determining the so-called "invasions stratospheric" in the tropopause, which may end up inside the main branch of the "jet stream". The negative anomalies occur only when the tropospheric air that rises to the edge of the stratosphere, causing the "invasions of tropospheric air." In the first case the thickness of the troposphere undergoes a lowering linked to a cyclonic circulation (cyclogenesis), more or less deep, which determines conditions of marked instability "baroclinic", with the static stability which decreases in the lower part of the anomaly. In the second case the troposphere instead tends to rise toward the boundary of the stratosphere, to the action of a cyclonic circulation, with the static stability that instead increases more and more in the lower part of the anomaly, favoring an increase of atmospheric stability, starting from the average and lower layers. In such contexts, with flows of stratospheric air is very dry in the upper troposphere, it can cause the phases of severe weather which can also result in treacherous storm-healing systems are able to download in a few hours of torrential rain which can cause disastrous flash flood that have marked the history of our country.
But how can we identify the invasions of dry stratospheric air on the high troposphere?
Usually, in order to detect the invasion of stratospheric air in the troposphere, we must resort to images of water vapor, where you can identify the extended dark lines that can stretch for hundreds of kilometers away. These dark lines, visible only with the aid of the image of water vapor, are called "Dark Stripe". Have recently been the subject of study seen the presence of a specific phenomenon which accompanies them. The "Dark Stripe" now represent the key parameters for the onset of rapid cyclogenesis (especially if they pass over areas "baroclinic" in the lower layers), phenomenology and the cloudiness associated with the "Jet Crossing", but also for the growth and 'explosion, sometimes sudden (not always predictable), convective activity along the anterior margin of these black stripes.
It is now well established in the face of a "Dark Stripe" can be the source of very violent storms with strong "updrafts" that may develop in thermo-dynamics not exactly optimal, with "vertical thermal gradients" not very intense. In this case, the bursting of the storm is going to locate right at the dividing line between the very cold and dry stratospheric air flowing over the warmer air and very moist troposphere. The strong "hygrometric vertical gradient" that is created, along the line of demarcation, when associated with originating conditions of marked instability in the tropospheric, can be longer sufficient to trigger the so-called fuse thunderstorm, which will tend to assume characteristic autorigeranti. The items listed can easily produce mesoscale convective systems insidious and dangerous "Cluster storm" that can download large loads precipitation within a few hours, especially in areas where the particular orography of the territory exacerbates the phenomenon of "stau". Regarding the storm Catania images of water vapor are very clear in this regard, in highlighting a "Dark Stripe", a wide dark line extending from the low Calabria up to the sea area in front of the coast of eastern Sicily.
This strand dark in the images of water vapor, highlights the "dry intrusion" which provided a strong emphasis convective activity, creating the strong updrafts that built the huge "storm Cluster" on Catania, head of the storm which flooded the city of Catania. The presence, in the lower layers of air saturated, humidified over the Ionian Sea, carried by a moderate ventilation, E-NE and NE, called the "CUT-OFF" North African and its accompanying minimum baric to the ground, he made even stronger than the so-called "vertical humidity gradient" that is immediately associated with pre-existing conditions of instability in the troposphere, associated with the passage of the "CUT-OFF" and the intense "Vertical Wind Shear" active in the Ionian Sea. The "Shear positive", with strong westerly winds at high altitude (500 hpa) over a sliding component in the north-east in the lower layers (850 hpa) within a cyclonic circulation, along with the "dry intrusion", had a role of no small importance in the formation storm, creating a significant "gap" in the middle layers of the troposphere.