The dynamics of the atmosphere in the development of tornadic events in Greece using the Weather Research and Forecasting Model (WRF)

Doctoral Dissertation uoadl:1308932 1276 Read counter

Unit:
Τομέας Γεωγραφίας - Κλιματολογίας
Library of the School of Science
Deposit date:
2014-04-08
Year:
2014
Author:
Ματσαγγούρας Ιωάννης
Dissertation committee:
Παναγιώτης Νάστος, Αναπλ. Καθηγητής ΕΚΠΑ (επιβλέπων), Σεραφείμ Πούλος, Αναπλ. Καθηγητής ΕΚΠΑ, Ιωάννης Πυθαρούλης, Επίκ. Καθηγητής ΑΠΘ
Original Title:
Η δυναμική της ατμόσφαιρας στην εμφάνιση σιφώνων στον Ελλαδικό χώρο με την χρήση αριθμητικού μοντέλου καιρού μέσης – κλίμακας WRF (Weather Research and Forecasting Model)
Languages:
Greek
Translated title:
The dynamics of the atmosphere in the development of tornadic events in Greece using the Weather Research and Forecasting Model (WRF)
Summary:
The objective of this PhD thesis was to study the dynamics of the atmosphere
that favour the development of tornadoes (TR), waterspouts (WS) and funnel
clouds (FC) over Greece within the period 1709-2012 from the point of view of
Climatology, Synoptic Meteorology and Numerical Weather Prediction. The study
area was emphasized over west Greece and south Aegean Sea. An online Greek
tornado report system was developed to record any tornadic activity over Greece
by the University of Athens (http://tornado.geol.uoa.gr/). A total of 612
tornadic events (TE) were recorded, within 405 unique days and categorized by
type as: 171 TR, 374 WS and 67 FC from 1709 to 2012. The impact of tornadic
activity was significant to structural facilities and to human life (114
injuries and 29 fatalities). Besides, 27.73 % of tornadic events were
characterized in terms of intensity as T4 of TORRO scale. The annual mean of TE
(2000-2012) over Greece was calculated to 42.15 events/year (10 TR/year, 27,69
WS/year), while the spatial annual mean was estimated to 3.19 events/104km2.
The most vulnerable area was characterized the west Greece with TE 19.09/year
(5.08 TR/year and 9.69 WS/year). TR exhibited an annual mean rate of 2.85
TR/year over NW Peloponnese, while WS events showed a maximum occurrence over
north Crete and Corfu, 10 WS/year and 6.92 WS/year, respectively. The seasonal
distribution of TE, TR and WS indicated autumn as the dominant season, while
tornadic days during autumn were estimated 4.75 days for TR and 7.17 days for
WS events. October was the month with the maximum frequency for TR, followed by
November; with an exception over the region of Macedonia where the maximum
frequency occurred during June and July. The monthly distribution of WS days
revealed October as the dominant month, followed by September. 75 % of TE were
developed between 08:00 and 15:00 UTC, while the diurnal variation of TR showed
a maximum from 11:00 to 13:00 UTC, in contrast to WS diurnal variation that
exhibited two maxima: between 07:00-09:00 UTC and 14:00-15:00 UTC. During
autumn season, the mean composite synoptic conditions of TR days over west
Greece displayed a large trough along the central and southern Italy at 500 hPa
isobaric level, and a closed cyclonic circulation over the Gulf of Taranto at
mean sea level (MSL). The same mean daily composite synoptic conditions were
characterized WS days over west Greece. During autumn season the mean daily
composite synoptic conditions during WS days over south Aegean Sea showed a
large trough line along the eastern parts of Greece at 500 hPa isobaric level,
and a combination of high pressure over central Europe with the low pressures
over SE Mediterranean Sea at MSL. During autumn the maximum daily composite
anomaly was depicted at 500 hPa isobaric level, in contrast to winter when the
maximum daily composite anomaly was calculated at the pressure level of 925 hPa
and MSL. During autumn the maximum daily composite anomaly of WS days was
observed at the isobaric level of 500 hPa. 48% of TR events, that occurred over
west Greece, developed in the warm sector of the cold front (pre - frontal
events) and in a distance less than 50 km from the active cold front line,
while the 27% of TR events developed in the cold area of the cold front (after
the passage of the front). There was not detected any correlation between warm
fronts (pre-frontal and post- frontal activity) and TR events. During autumn
season, the favour synoptic types over west Greece for TR were the Type-7 and
Type-12, with a frequency of 3.56 % and 6.79 % TR days, respectively, while for
WS were the Type-7, 3 and 12 with a frequency of 3.8 %, 1.23 % and 3.85 % WS
days, respectively. During autumn, the dominant synoptic types for WS
development over south Aegean Sea were the Type-11, 6 and 13, with a frequency
of 2.86 %, 0.7% and 1.66 % WS days, respectively. The thermodynamic profile of
the atmosphere during WS days over south Aegean Sea revealed atmospheric
conditions associated with insignificant unstable conditions retrieved from the
thermodynamic indices (LI, SW, K, CAPE, BRN) and a passage of a minor trough at
the middle atmosphere over east parts of Greece. The mean wind speed in the
lower atmosphere during WS days over the south Aegean sea, exhibited values
less than 15 knots, while the mean wind direction was calculated from NW
directions. In addition, the vertical wind profile showed a successive backing
and veering up to the level of 500 hPa. The temperature differences between the
levels of 1000 hPa and 500, 700, 850 and 925 hPa, as well as SST and the
aforementioned upper air isobaric levels showed quassi similar differences on
seasonal basis. SST over south Aegean Sea during autumn WS days showed a range
of SST values from 25.35 to 16.50 °C (mean 22.77 °C), in contrast to winter,
when SST was calculated 19.10-15.3 °C (mean 19.1 °C).
Numerical simulations with the use of WRF-ARW numerical model confirmed its
ability to reproduce/simulate the atmospheric conditions and to assess the
spatiotemporal evolution of the maximum values of the tornadogenesis indices
such as EHI, SRH, MCAPE, at least 12 forecasting hours prior the onset of TR
and quite near to the location of formation. The study of the orography effect
by applying numerical simulations of TR events associated with synoptic force,
illustrated that topography played an important role in the development of TR
in Thebes of Boeotia on 17/11/2007 and in Vrastama of Halkidiki on 12/2/2010,
in contrast to the numerical simulations of TR events over west Greece (in
Vlychos of Lefas on 21/9/2011 and in Varda of Ilias on 25/3/2009).
Keywords:
Tornado, Waterspout, Thermodynamic instability indices, Numerical simulations, Weather Research and Forecasting Model
Index:
Yes
Number of index pages:
21-41
Contains images:
Yes
Number of references:
240
Number of pages:
358
document.pdf (54 MB) Open in new window