The Science Behind Sandy Adam Sobel Columbia University

The Science Behind Sandy

Adam Sobel

Columbia University

nytimes.com22 23

24

25

2627

28

29

30

Blake et al. (2013)NHC report on Sandy

numbers aredates in October

Yellow = tropical stormRed = cat 1 hurricaneMagenta = cat 2

Biography of a hurricane

Sandy’s grandparents:

The Madden-Julian oscillationand

the North Atlantic oscillation

The Madden-Julian oscillation – a natural fluctuation of the tropicalclimate

Source: Matt Wheeler, Centre for Australian Climate and Weather Researchcawcr.gov.au

Outgoing longwave radiation 15S-15N

Blue = rainyOrange = clear

longitude

time->

Aug 2011

Sep

Oct

Nov

Dec

Jan



longitude

time->

Aug 2011

Sep

Oct

Nov

Dec

Jan





longitude

time->

Aug 2011

Sep

Oct

Nov

Dec

Jan





longitude

time->

Aug 2011

Sep

Oct

Nov

Dec

Jan



Sandy formed as an active MJO passed through the northAtlantic basin – so it had Pacific ancestry

Blake et al. (2013), NHC report on Sandy

--

The other player was the North Atlantic Oscillation, naturalfluctuation of the high-latitude jet stream

source: ldeo.columbia.edu

+ -

--

The other player was the North Atlantic Oscillation, naturalfluctuation of the high-latitude jet stream

source: ldeo.columbia.edu

+

Jet stream shifted south,cold in eastern US

Source: NOAA CPC, www.cpc.ncep.noaa.gov

+ -

In mid-October the NAO was heading into strongly negativeterritory, conducive to cold-air outbreaks in eastern US

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 thewestern north Atlantic

500 hPa geopotential height

Jet sream H

Oct. 22, 2012, NHC names Tropical Depression 18, thena few hours later upgrades to Tropical Storm Sandy

GOES visible satellite image 10/22 at 15 UTChttp://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, 10/28http://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. Katrinaclimatecentral.com

How rare an event was this?

Sandy

1903

1938

1893

IreneDonna (1960)

Historic Hurricane landfalls in NY/NJ Figure by Tim Hall, NASA GISS

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.

T. Hall and A. H. Sobel, Geophys. Res. Lett., in press.

Sandy1903 “vagabond”

synthetic storms

Sandy

Scileppi and Donnelly, 2007, Geochem. Geophys. Geosys.

Storm tide at Battery highest ever recorded by tide gauge(since 1920); 1821 may have had larger storm surge

Climate change influence?

Zhao et al. (2009) Journal of Climate

Our latest and best models give a mixed predictions about howthe number of hurricanes will change in a warming climate

Fractional changeIn number of N. Atlantic Hurricanes

Different climate models

Dan Shaevitz, Suzana Camargo, US CLIVAR HurricaneWorking 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 HurricaneWorking Group, NOAA/GFDL model

But we do have some confidence that the most intense storms will become stronger still

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.

Nicholls and Cazenave, 2010, Science

1 meter

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 this model, 1000-year floodbecomes 70-year

www.columbia.edu/~ahs129/home.html

GFS Ensemble run Wednesday 10/24 – same model, 20 slightlydifferent initial conditions

Documents

The Science Behind Sandy Adam Sobel Columbia University