2009/05/25 case over Europe

RDT_v2013

Severe Thunderstorm event over France, with heavy gusts and heavy hail, associated with convergence line
Strong diurnal convection over Adriatic edges

1-Animation of RDT Convective cells
2-Additional attributes
3-Rapid cell triggering
4-Precocity
5-Development of severe thunderstorms
6-NWP convective environment

RDT/PGE11 convective cells

RDT v2013 has been processed during the 25th May 2009, using following data

available channels of MSG

IR108 for tracking
WV6.2, WV7.3, IR10.8, IR8.7 and IR12.0 for convective discrimination
VIS0.6 for overshooting top confirmation

NWP data for convective mask , LI predictor and tropopause fields
Cloud type (CT-PGE02) for masking cloud-free areas, and attributes cloud cell type and cloud cell phase
Cloud Top Temperature Height (CTTH-PGE03) for cloud cell Top Pressure attribute
Convective Rain Rate (CRR-PGE05) for maximum rain rate attribute of cloud cell
Lightning data from EUCLID network over Europe, used only for pairing cloud and strokes (not forcing diagnosis)

As a result, one can notice the good depiction and tracking of convective cells.
MCCs are quite well tracked, and their de-classification when being inactive appears to be relevant

Around 13h UTC near Adriatic, diurnal convection begins, and appears to be at its maximum around 15UTC. Here again all cells are well depicted

Most systems correspond to active MCCs or CBs, and if not, they reveal significant cooling. They are obviously convective, even if they don't always degenerate in Thunderstorms.

The number of overshooting top detection (OTD) is quite significant, and some U-shape-like MCS even reveal more than one overshoot

RDT loop for the whole day

anasyg 18UTC

Synthetic analysis at 18UTC

Additional attributes

This release of RDT allows to display additionnal information concerning overshooting top detection (OTD):

The knowledge of vertical IR10.8-morphology of cloud cell allows to seek and analyse overshooting tops
The availability of attributes from other channels (WV and VIS) and NWP data (for tropopause diagnosis) is used to confirm or not these features
This gives another sign for convective activity

Overshoot characteristics available in RDT :
- minimum brightness temperature
- maximum BTD(WV6.2-IR10.8)
- Negative delta temperature with tropopause (OT over and colder than tropopause)

Tower base cell's attributes, including OTD description

slot 13h, on 25th May 2009.
Tower base and 2nd level contours.
1st level catch the whole system, whereas
2nd level highlights here U-shape top
2 overshoots are here diagnosed, marked by green dots

Rapid cell triggering

A Rapid triggering cell is found at 10h11 UTC over Serbia, in warm category. The cell was cooling during 45 minutes before the diagnostic, and it last several hours . This cell is out of the Meteorage coverage, so no pairing is observed. Nevertheless, it is obviously a rapid developping thunderstorm.

slot 10h00 UTC (valid 10h11).
First diagnosis of convective cell with strong cooling (left figure)

slot 14h30 UTC (valid 14h41) after 4h30 tracking, just before decaying stage
light electrical activity (right figure)

After

Precocity of RDT convective diagnostic vs lightning

Italy

From 11h56 three convective cells are diagnosed very early by RDT , in warmest category (minimum temperatures between -12° and -23°).
That was obviously a pretty good precocity when looking at following slots. Even if one of these cells did not degenerate, the othersshow a convective development, with 2 first flashes at 13h11, i.e. one hour and a half later !
An isolated cell is also diagnosed in the southern Italy at 12h41 around -20°, rising up to -45° in 15 min (-102°/h !!), and getting first flash at 13h11 arounf -65°. This is a very good example of rapid developping thunderstorm.

slot 11h45 UTC (valid (11h56)	slot 12h30 UTC (valid 12h41)	slot 13h00 central Italy	slot 13h00 south Italy
slot 12h45 UTC (valid 12h56)	slot 13h00 UTC (valid 13h11)

Germany

From noon, a group of convective cells rises in the south-west of Germany, merging to give a large thunderstorm
- slot 11h15 => A first cell is diagnosed, with minimum temperature of -35° , after 45 min tracking and a weak cooling.
- slot 11h45 => A second cell, which will become the main one, has risen at the same time some km southward, but is diagnosed 30min later.
    - slot 12h00 => Lightning activity begins in the main cell, and an isolated flash appears inside a third new diagnosed small cell, which will merge into the main one 30 min later
        - slot 12h45 => Lightning activity begins in the first cell, 1h30 after the convective diagnosis by RDT
           - slot 14h30 => the first cell merges finally into the big main one
              - slot 16h30 => the big cell is de-classified , and continue to dissipate until 19h00

Globaly speaking, one can consider that it corresponds to a quite good anticipation of 15 min by RDT, for a 4 hours duration system, associated with a strong electrical activity.
Cell by cell, the evaluation is :
- the first cell becomes electrical 1h30 after its convective diagnosis
- the main one is diagnosed 15 minutes before electrical activity
- the third one is diagnosed at the same time than the start of electrical activity

First diagnosed cell - slot 11h15	First impacts in 2nd main cell - slot 12h	Big merged cell before dissipation

Development of rapid and severe thunderstorms

Rapid Thunderstorms associated with the convergence line starts slightly before 16h UTC in the south of France, North of Pyrenees. They are detected and diagnosed at 16h15 by RDT, but lightning already occur at this time
The regeneration point of convergence line is quite well identified, through trajectory of new diagnosed cells .
Large MCS north of Toulouse show successive OTD on its southern edge : at 16h-16h15, then 16h45-17h, and 17h30.
This highlights strong updrafts on its regenerative part.

15h45	16h - 1 OTD	16h15 - 3 OTD	16h30 - 2 OTD
16h45 - 2 OTD	17h - 3 OTD	17h15 - 1 OTD	17h30 - 4 OTD
17h45 - 1 OTD	18h - 1 OTD	18h45 - 2 OTD	19h45 - 2 OTD

Mosaic of RDT cells over France from slots 15h45 to 19h45 UTC (valid 11min later, from top left to bottom right).

Convective and non convective environment

A analysis of convective indexes issued from NWP fields show that RDT cells fit well with pre-suposed unstable areas.
A convective mask (bottom right) is derived from severall NWP convective indexes (among which Lifted Index), giving non convective value when ALL indexes are stable, and convective value when at least one index is unstable.
None cell is diagnosed in the "non convective" mask areas.
Most active systems occur inside the pre-supposed convective areas

RDT cells at 13UTC

Lifted Index (unstable from <0 values = brown/red) Convective mask (black = at least one NWP index unstable, white =all stable)

Those fields are computed at each slot and used as a guidance for lowering False Alarm during less active situations.