Identify and interpret atmospheric phenomena
Under influence of frontogenesis the development of two waves within a frontal system is being studied.
This case study addresses the development of two waves within a frontal system over Central and East Europe. Waves are substructures of a cold front which indicates the initial stage of (secondary) cyclogenesis.
For this investigation two different waves will be analyzed using single satellite images as well as combined channel products. Moreover conceptual models which base on a certain selection of numerical parameters will be introduced. Based on the development of the two different wave systems, the quality of the background information (satellite imagery, NWP-field) can be assessed.
The case study describes two events of convection that occurred over Ukraine on 9th and 10th July 2004. Consequently heavy rain and rail were observed.
This case study addresses the formation of a mesoscale convective systems over the Ukraine on 9th and 10th July 2004 associated with heavy rainfall and hail. Cloud top temperatures of up to -70 degrees Celsius were observed. Moreover it should be noted that the Carpathian Mountains played a central role, since the mountain ridge triggered a set of cells.
In this study the development will be observed closely based on satellite imageries and the NWP-field. Since the vertical stratification is essential for the formation of convection, stability indices will be assessed as well.
This case study is about a typical formation of a squall line moving from France towards Germany.
During the 18th August a frontal cloud pattern moved from Western France to Central Germany. From noon until the evening this cloud pattern transformed into a squall line due to cyclonic vorticity advection induced by a short wave trough. From the afternoon to the evening a mesoscale low with negative surface pressure tendencies developed east of the squall line. In combination with the increasing temperature contrast between the front and rear of the squall line, the velocity of the wind reached 100 km/h. Gusts of up to Beaufort 9 (flat areas) and 11 (mountainous regions) and precipitation of about 30 mm over Eastern France and and Western Germany were observed.
The case describes two convective events that happened end of May 2005 over Greece and Turkey and over Western Europe.
In the case study two types of convective development are observed and addressed. At the 30th of May a broad N-S oriented frontal zone is covering Western Europe. On the leading side of this front several convective cells emerge. A further index for frontal intensifications is the dry intrusion which can be detected in the WV imagery can be observed.
Apart from that several cells emerge in Greece and Turkey. The convective development in Greece and Turkey can be characterized as fair weather convection. In this case study it will be shown that both convective developments have similarities but also differences. Based on satellite imageries and derived numerical parameters these differences and similarities will be accentuated. However both weather events were associated with hail and lead to major damages in agriculture.
A classical example of prefrontal convergence occurred on 30 July 2005 as a long line of convective cells stretching over Central Europe developed.
On July 30th 2005 a prefrontal convergence line formed at the leading edge of a cold front. The long convergence line stretched from Italy over Austria into Poland and the Baltic States. Based on satellite imagery a sequence of thunderstorms could be observed. Moreover it should be noted that this form of prefrontal convergence is clearly linked to the diurnal cycle. As night sets in, most of the cells dissolve.
Since convection is a rather small scale phenomenon, it can be beneficial to address high resolution limited area models such as ALADIN-AUSTRIA. The comprehensive analysis of ALADIN-AUSTRIA revealed converging motions at 925 hPa and the divergence (e.g. outflow of air near the cloud top) at 700 hPa. In regard to the stability analysis the nowcasting tool GII (Global Instability Index) provided by EUMETSAT proved to be useful.
During the 9th and 10th July the Baltic States and Finland experienced heavy rain as a wave-cloud formed in moist and warm south-easterly air stream.
This study concentrates on two areas at the opposite sides of the low pressure area. The objective is to provide a detailed insight into the mechanisms that govern the formation of convection within a cold front (Finland) as well as prolonged rain within an occluded front (Lithuania).
In Lithuania the event was characterized by extreme rainfall (locally more than 250 mm in 3 days), leading to floods and severe damage. The south-westerly gusts on the 10th August caused uprooting of trees and further economic loss in excel of 45 million Euro. In Finland the most remarkable events were those connected with the passing of the cold front in the evening of August 9, associated with the intensive precipitation and lightning.
November 2005 severe snowfall had major effects in Western Europe. Snowfall caused an outage of power plants leaving people without heating and electricity.
The case study describes the merging process of a comma-like cloud feature with a cold front cloud band. The term instant occlusion is used because the mature stage of the development shows a cloud spiral similar to that of a normal occlusion. But the meteorological processes are totally different from an occlusion process where advection of cold air lifts warm air. The process took place in an area of cold air without a warm front being present.
The subsequent snowfall caused an outage of power plants leaving people without heating and electricity for several days.
This study illustrates an interesting case of a cold front in cold air advection on which two waves are developing. The origin of these waves is different which is explained.
This case study follows a cold front propagating from the Atlantic towards eastern Europe at the leading side of a deepening upper level trough. Special attention is paid to two waves developing on the cold front. Both of them show similar phases of development, from the first appearance of a cloud bulge to the formation of a cloud spiral.
The whole process can be observed in several types of satellite images: IR, WV and Airmass RGB composite. In the IR images the formation of the both wave bulges, intensification of the frontal cloudiness and cloud spiral development can be followed. The WV images enable the detection of the jet and the intrusion of dry stratospheric air. In the Airmass RGB the different air mass types as well as the position of the jet stream can be detected.
On 26th May the transition of a cold front trough Turkey was linked to serious convective developments. According to several reports the weather event was associated with hail.
The case study describes s series of convective developments which took place in front of a cold front as well as within the transition of that cold front. On 25th May first convective development were noticed over Romania at the leading edge of the front. Within the next few hours the convective developments started ahead of the front and were induced by orography.
During the night the convection was linked to the further movement of the cold front. The explosive convective development over Turkey on 26th May is nicely depicted in the set of radar-image and satellite images.
On 27 July 2006 such short-living-convective cells developed over Germany. These convective events marked the end of a long lasting heat period which characterized July 2006.
The case study describes the development of severe convection over Germany on 27 July 2006, which took place in the forefront of a cold front and an upper air trough. With the troughs approach the potential unstable warm and moist air over Central Europe was lifted. Supported by solar isolation, single cells and multi cells as well as super cells developed over eastern France and Germany, finally forming a north-south oriented squall line. Heavy precipitation of up to 30 mm/h and gusts of up to Beaufort 10 were registered.
A five day period of dense fog was overcasting London Heathrow during Christmas 2006 severely disrupting air traffic.
This case study presents the synoptic analysis of an event that took place from the 18th to 23th December over the UK. During this period dense fog was covering many places in the UK causing extremely bad conditions for aviation. For a busy international airport like Heathrow the cancellation of hundreds of flights just at the peak travel season (a few days before Christmas) meant chaos and significant economic loss. Changes in travel plans affected at least tens of thousands of passengers.
Fog itself is a common event on the British Isles at this time of the year. However, the duration of the episode justifies a closer look at the event. In addition, the visibility within the fog was at times very low, and this heavily affected the air-traffic even at airports having the most advanced instrumentation for low-visibility flight operations.
This study concentrates only on the area in the southeastern UK, but basically similar synoptic conditions with reduced visibility at times prevailed also on the European continent during this episode. What makes this case study differ from many other case studies is the absence or small influence of atmospheric fronts or dynamic forcing (such as PVA or PV anomalies).
On 18 September 2007 Slovenia received 303 mm of rain in shy 24 hours. The result were flash floods and huge material damage.
This case-study presents the analysis of catastrophic flash floods in Slovenia that occurred on 18 September 2007. The flooding caused five casualties and huge material damage, estimated to more than 150 million Euro.
NWP models forecasted precipitation amounts of up to 100 mm/24h. That was the reason that the forecaster issued a warning for the precipitation at a rate of more than 100 mm/day, but the real values were much higher.
Besides analyzing synoptic and mesoscale conditions, that caused the extreme amount of precipitation, the objective of this study is also to show how nowcasting material can help a forecaster to issue additional warnings.
The synoptic analysis shows that on the day of the catastrophic event the area of low pressure was situated over the Northern Europe. A cold front was approaching the Alps and over Slovenia a series of prefrontal convective developments took place. In many regions in Slovenia the precipitation values were extremely high (>100 mm/day) with the maximum precipitation of 304 mm/24h officially measured in Kneske Ravne.