Transcript Retrospective analysis of NE Atlantic weather

Regional storm climate and related
marine hazards in the NE Atlantic
Hans von Storch und viele Kollegen
Institute for Coastal Research,
GKSS, Germany
1. How to determine decadal and longer variations in
the storm climate?
2. How has the NE Atlantic storm climate developed
in the last few decades and last few centuries?
3. How is the extratropical storm climate variability
linked to hemispheric temperature variations?
4. How did wind-impact on storm surges and ocean
waves develop in the past decades, and what may
happen in the expected course of anthropogenic
climate change?
1. How to determine decadal and longer variations in
the storm climate?
2. How has the NE Atlantic storm climate developed
in the last few decades and last few centuries?
3. How is the extratropical storm climate variability
linked to hemispheric temperature variations?
4. How did wind-impact on storm surges and ocean
waves develop in the past decades?
Changes of the wind climate
• Climate = statistics of weather, as given
by distributions or parameters thereof,
such as means, percentiles etc.
• Changes of wind stats difficult to
determine, because of changing
observation practices and environments.
• Almost all long record of wind
observations are inhomogeneous, i.e.,
they do not only reflect changes of the
wind statistics but also other factors,
such as observation method, practice,
location, analysis method ….
10-yearly sum
of events with
winds stronger
than 7 Bft in
Hamburg
Pressure based proxies
• Pressure readings are usually homogenous
• Annual percentiles of geostrophic wind
(e.g., 95 or 99%iles)
• Annual frequency of 24 hourly local
pressure change of 16 hPa in a year
• Annual frequency of pressure readings
less than 980 hPa in a year
1. How to determine decadal and longer variations in
the storm climate?
2. How has the NE Atlantic storm climate developed
in the last few decades and last few centuries?
3. How is extratropical storm climate variability
linked to hemispheric temperature variations?
4. How did wind-impact on storm surges and ocean
waves develop in the past decades?
Stockholm
Lund
Time series of pressure-based storminess indices derived from pressure readings in Lund (blue) and Stockholm
(red). From top to bottom: Annual number of pressure observations below 980 hPa (Np980), annual number of
absolute pressure differences exceeding 16 hPa/12 h (NDp/Dt),
Intra-annual 95-percentile and 99-percentile of the pressure differences (P95 and P99) in units of hPa. From
Bärring and von Storch, 2005 (GRL)
1. How to determine decadal and longer variations in
the storm climate?
2. How has the NE Atlantic storm climate developed
in the last few decades and last few centuries?
3. How is the extratropical storm climate variability
linked to hemispheric temperature variations?
4. How did wind-impact on storm surges and ocean
waves develop in the past decades?
“Forced” simulation, 1000-2000
• Simulation with climate model exposed
to estimated volcanic, solar and GHG
forcing.
• Number of strong wind events per
season (wind at 10 m;  8 Bft, gales;
every 12 hours) were counted.
(11-yr running means)
Fischer-Bruns et al., 2005
Warming
and Storms in the N Atlantic
N Atlantic
NH Temp & NA storm count:
No obvious correlation in simulated historical times
1. How to determine decadal and longer variations in
the storm climate?
2. How has the NE Atlantic storm climate developed
in the last few decades and last few centuries?
3. How is the extratropical storm climate variability
linked to hemispheric temperature variations?
4. How did wind-impact on storm surges and ocean
waves develop in the past decades?
Aber wie sieht es regional
und lokal aus?
Hydrodynamisches Modell
der Nordseezirkulation
Katja Woth
Globales Geschehen
Dynamisches Downscaling
Pegel St. Pauli
Zusammenarbeit u. a. mit BAW, BSH,
ALR Husum, FSK Norderney,
Hamburg Port Authority u.a.
Empirisches Downscaling
t≤T
Change of # Bft 8/year
t≥T
Weisse et al., J. Climate, 2005
Stormcount 1958-2001
Scenarios for 2085
A2 - CTL: changes in 99 % - iles of wind speed (6 hourly, DJF): west wind
sector selected (247.5 to 292.5 deg)
HIRHAM
RCAO
Woth et
al., 2005
1. How to determine decadal and longer variations in the storm climate?
Use homogenous proxies for storminess.
2. How has the NE Atlantic storm climate developed in the last few decades and last few
centuries?
An intensification in 1960-1990; thereafter activity has ceased
somewhat. No significant changes since 1800.
3. How is the extratropical storm climate variability linked to hemispheric temperature
variations?
Model simulation indicate that there is no obvious link during historical
times, but that parallel signals a probable in the course of emerging
anthropogenic climate change.
4. How did wind-impact on storm surges and ocean waves develop in the past decades?
Storm surges as well as ocean wave extremes develop mostly parallel to
wind conditions; no significant increases in the past, except for an
ongoing increase in the Southern North Sea.