The Science Behind Sandy
Adam Sobel
Columbia University
Biography30of a hurricane
29
28
27
26
25
24
22 23
numbers are
dates in October
Yellow = tropical storm
Red = cat 1 hurricane
Magenta = cat 2
Blake et al. (2013)
NHC report nytimes.com
on Sandy
Sandy’s grandparents:
The Madden-Julian oscillation
and
the North Atlantic oscillation
The Madden-Julian oscillation – a natural fluctuation of the tropical
climate
Outgoing longwave
radiation 15S-15N
Aug 2011
Sep
Oct
Nov
time->
Blue = rainy
Orange = clear
Dec
Jan
longitude
Source: Matt Wheeler, Centre for Australian Climate and Weather Research
cawcr.gov.au
The Madden-Julian oscillation – a natural fluctuation of the tropical
climate
Outgoing longwave
radiation 15S-15N
Aug 2011
Sep
Oct
Nov
time->
Blue = rainy
Orange = clear
Dec
Jan
longitude
Source: Matt Wheeler, Centre for Australian Climate and Weather Research
cawcr.gov.au
The Madden-Julian oscillation – a natural fluctuation of the tropical
climate
Outgoing longwave
radiation 15S-15N
Aug 2011
Sep
Oct
Nov
time->
Blue = rainy
Orange = clear
Dec
Jan
longitude
Source: Matt Wheeler, Centre for Australian Climate and Weather Research
cawcr.gov.au
The Madden-Julian oscillation – a natural fluctuation of the tropical
climate
Outgoing longwave
radiation 15S-15N
Aug 2011
Sep
Oct
Nov
time->
Blue = rainy
Orange = clear
Dec
Jan
longitude
Source: Matt Wheeler, Centre for Australian Climate and Weather Research
cawcr.gov.au
Sandy formed as an active MJO passed through the north
Atlantic basin – so it had Pacific ancestry
Blake et al. (2013), NHC report on Sandy
The other player was the North Atlantic Oscillation, natural
fluctuation of the high-latitude jet stream
-
+
source: ldeo.columbia.edu
--
The other player was the North Atlantic Oscillation, natural
fluctuation of the high-latitude jet stream
-
+
source: ldeo.columbia.edu
-
Jet stream shifted south,
cold in eastern US
In mid-October the NAO was heading into strongly negative
territory, conducive to cold-air outbreaks in eastern US
+
Source: NOAA CPC, www.cpc.ncep.noaa.gov
-
And on Oct. 20, 2012, blocking high (typical of negative
NAO) moves into the western north Atlantic
500 hPa geopotential height
And on Oct. 20, 2012, blocking high moves into the
western north Atlantic
500 hPa geopotential height
Jet sream
H
Oct. 22, 2012, NHC names Tropical Depression 18, then
a few hours later upgrades to Tropical Storm Sandy
GOES visible satellite image
10/22 at 15 UTC
http://rammb.cira.colostate.edu/
Wed. 10/24 – landfall in Jamaica (cat 1)
Cuba next day 10/25 (cat 3)
Deterministic GFS 6-day forecast for Monday night 10/29,
made Wed. 10/24
Deterministic ECMWF 6-day forecast for Monday night 10/29,
made Wed. 10/24
Interaction with extratropical
system, Fujiwhara effect,
landfall
Interaction with extratropical
system, Fujiwhara effect,
landfall
Visible MODIS satellite image from Saturday, 10/28
http://www.wunderground.com/blog/JeffMasters/
Animation from GFS forecast, images by Kyle Griffin, U. Wisc. PhD student
Sandy near landfall was declared “post-tropical” –
note high asymmetry (false color IR)
Sandy near landfall was declared “post-tropical” –
note high asymmetry (false color IR)
Because of this, no hurricane warnings were
issued north of NC, causing some confusion…
NYC storm surge
• Landfall in Jersey at sharp angle
moving westward
• Winds are stronger to right of track
• Onshore winds
• Very large wind field
• Worst possible situation
Sandy vs. Katrina
climatecentral.com
How rare an event was this?
Historic Hurricane landfalls in NY/NJ
Figure by Tim Hall, NASA GISS
1903
Sandy
Donna (1960)
Irene
1893
1938
Synthetic track model says NJ landfall at cat 1+ at Sandy’s
angle is a 700 yr event. Flood return time is probably shorter.
Not accounting for climate change.
synthetic storms
Sandy
1903 “vagabond”
T. Hall and A. H. Sobel, Geophys. Res. Lett., in press.
Storm tide at Battery highest ever recorded by tide gauge
(since 1920); 1821 may have had larger storm surge
Sandy
Scileppi and Donnelly, 2007, Geochem. Geophys. Geosys.
Climate change influence?
Our latest and best models give a mixed predictions about how
the number of hurricanes will change in a warming climate
Fractional change
In number of N.
Atlantic Hurricanes
Different climate models
Zhao et al. (2009) Journal of Climate
But we do have some confidence that the most intense storms
will become stronger still
Dan Shaevitz, Suzana Camargo, US CLIVAR Hurricane
Working Group, NOAA/GFDL model
But we do have some confidence that the most intense storms
will become stronger still
Dan Shaevitz, Suzana Camargo, US CLIVAR Hurricane
Working Group, NOAA/GFDL model
But Sandy was not so intense (cat 1) at
landfall… the large surge was due to:
• Its huge size, due to extratropical transition – we know
nothing about what warming will do to that;
• Its track – we know little about what warming will do to that,
but…
Distorted jet, a la Sandy, has been associated with polar
amplified global warming (Francis and Vavrus 2012)…
But climate models give the opposite result
(E. Barnes, L. Polvani, AHS)
The really clear and simple link to climate is via sea level rise.
1 meter
Nicholls and Cazenave, 2010, Science
With 1m sea level rise, depending on projections of TC change,
can get increase of ~2-20 in flood frequency. (i.e. 20 means
100-year flood becomes 5-year)
Lin et al. 2012, Nature Climate Change 2, 462-467.
With 1m sea level rise, depending on projections of TC change,
can get increase of ~2-20 in flood frequency. (i.e. 20 means
100-year flood becomes 5-year)
Lin et al. 2012, Nature Climate Change 2, 462-467.
With 1m sea level rise, depending on projections of TC change,
can get increase of ~2-20 in flood frequency. (i.e. 20 means
100-year flood becomes 5-year)
With this model, 1000-year flood
becomes 70-year
Lin et al. 2012, Nature Climate Change 2, 462-467.
www.columbia.edu/~ahs129/home.html
GFS Ensemble run Wednesday 10/24 – same model, 20 slightly
different initial conditions