ASSOCIATIONS BETWEEN SST/SIC CONDITIONS AND POLAR LOWS

M.Vicomte (1) ,C. Claud (1), M. Rojo (1), P.-E. Mallet (1), T. Laffineur (2)

(1) CNRS/IPSL/LMD, Palaiseau, France (UPMC)(2) ENM, Météo France, Toulouse, France

CHARACTERISTICS OF POLAR LOWS (PLS)

o Very intense mesoscale storms < 1 000 km diameter, generally < 24 h lifetime

--> difficult to forecast.

o A maritime phenomenon, declining rapidly over land (because of the larger fluxes of heat and moisture from the ocean).

o Usually occur during winter season, between October and Marcho Formation requires a cold air outbreak over relatively warm watero Mean winds in excess of 25m/s, strong precipitation.

Polar Low (PL) 28 Oct 200802:08 UTCImage AVHRR NOAA 18

(http://www.sat.dundee.ac.uk/)

OBJECTIVES

Within WP1 core theme, our goal is :

TO BETTER UNDERSTAND THE ROLE OF THE SST AND SEA ICE CONDITIONS ON THE SPATIAL AND TEMPORAL DISTRIBUTION OF POLAR LOWS

Large interannual variability :• Few PL in October ≤ 2 per year• Much more in March with a maximum of

13 PLs in 2013

Formation areas of polar lows

Focus on Norwegian and Barents Seas (Noer et al., 2011)

CHARACTERISTICS OF POLAR LOWS

October November December

January February March

REPRESENTATION OF POLAR LOWS IN REANALYSES

(Laffineur et al., Monthly Weather Review, 2014)

Representation of PLs in reanalyses compared to observations between 1999 and 2001 :

• ERA-40 (1.125° resolution) : 24%

• ERA-I (0.75° resolution) : 45 %

Atmospheric reanalyses can however be used for studying the large scale circulation associated with development of PLs

LARGE-SCALE ATMOSPHERIC CIRCULATION FOR POLAR LOW DAYS

Composite standardized anomalies of Z500, SST-T500, PV300 and winds (ERAI) and significance during cold season for PL days

PL formation when :

• Negative geopotential height (Z500)

• Large instability (SST-T500 positive)

• Stratospheric intrusion at lower tropopause (PV 300 positive)

• Northerly winds at 925 hPa

Anomalies last 8-10 days

(Mallet et al , JGR Atmosphere, 2013)

Z 500 hPa

SST-T500

PV 300 hPa

Winds 925 hPa

FORMATION AREAS OF PLS

(Rojo et al, Tellus A, 2014

in revision)

Most of Pls form along the Norwegian Atlantic Current and other warm oceanic currents

~25% of PLs form at the edge of sea ice during 1999-2013 period

FORMATION OF POLAR LOWS IN LARGE SST GRADIENT : AN EXAMPLE

Example of polar low (21/02/2012) which formed at the edge of sea ice and lasted 2 daysStart in the Norwegian Sea and end in the Barents SeaFormation in high SST gradients. Trajectory followed wind direction at 925 hPa.

ERA-I winds at 925 hPa at 22/02/2012

SST and SIC on 21/02/2012 from OSTIA (Operational SST and SIC

Analysis)

06:12 21/02 02:32

23/02

CONNEXION BETWEEN SEA ICE AND FORMATION OF POLAR LOWS

A single case of Polar Low observed north of Svalbard, 8 January 2010

Sea Ice

Courtesy of Gunnar Noer, Norv Met Institute (NOAA-17 MOZAIKK 2009-01-16 17:40, polarlow.met.no/stars/)

A single case of Polar Low observed 16 January 2009 over Kara Sea during 1999-2013 period

INFLUENCE OF MID-WINTER BARENTS SEA SIC ON POLAR LOW FORMATION IN MARCH

Observations :• 0 PL in March 2007• 13 PL in March 2013

Why this difference?

INFLUENCE OF MID-WINTER BARENTS SEA SIC ON POLAR LOWS FORMATION IN MARCH

Differences between composites of SST, SST-T500, Z500 and winds in March for the years with negative anomalies of SIC (SI-) in January/February and years with positive anomalies (SI+)(lag of about 2 months)

For negative anomalies of SIC in January /February, atmospheric conditions are favorable to PL developments in March over the Barents Sea.

(Mallet, 2013)

SI- - SI+

(Mallet, 2013 PHD)

SI- - SI+

INFLUENCE OF WINTER BARENTS SEA SIC ON POLAR LOW FORMATION AT THE END OF THE SEASON

SIC january 2007 SIC january 2013

PLs march 2007 PLs march 2013

Analysis of SIC in January

Strong negative anomalies of SIC in January 2013 compared to 2007 over Barents Sea

Favorable conditions for formation of PLs

SIC maps from OISST data sets(NOAA Optimum Interpolation Sea Surface Temperature V2)

TEMPORAL DISTRIBUTION OF POLAR LOWS OVER NORDIC SEAS

Decrease of Polar Lows occurrences in NDJ

What is the impact of the Arctic summer sea ice extent on the early/mid-winter occurrence of polar lows?

(Rojo, M.)

INFLUENCE OF ARCTIC SUMMER SEA ICE EXTENT

ftp://sidads.colorado.edu/DATASETS/NOAA/G02135/Sep/N_09_area.txt

Arctic sea ice extent anomalies in September for 1979-2013

SST-T 500 hPa

INFLUENCE OF SUMMER SEA ICE EXTENT ON LARGE SCALE CIRCULATION IN MID-WINTER

In December

Z 500 hPa

PV 300 hPa

Winds 925 hPa

Correlation between SIC extent index in September and Z500, PV300, winds and SST-T500 in December

For positive anomalies of September SI extent, atmospheric conditions allow formation of PLs over the nordic seas

• We have observed that a large part of polar lows develop along relatively warm oceanic currents. Nevertheless 25% of them develop at the edge of sea ice where SST gradient is high.

• Polar Lows develop over open water areas. The retreat of sea ice the last years opens new areas of polar low formation.

• Reduced sea ice over the Barents Sea in mid-winter creates more favorable conditions for PL development at the end of the season.

• Arctic sea ice decline at the end of summer may have impact on the lower activity observed in early/mid winter during the last years.

CONCLUSIONS

• The associations are investigated in climate simulations :o ECHAM5/MPI-OM (1.875°-1.5° resolution)

WORK IN PROGRESS

SIC A1B-20C

SST-T500 A1B-20C

Similar features, more or less marked, for the 3 scenarios (B1, A1B, A2) : • Large retreat of SIC to the north • Increased stability over the north Atlantic Ocean

Northward shift of favorable regions for polar low formation

Comparison of SIC and SST-T500 in NDJFM between 2 scenarios of ECHAM5/MPI-OM:

• A1B (2070-2099)• and 20C (1970-

1999)

Thanks for your attention

SST

SIC

INFLUENCE OF WINTER SIC/SST ON POLAR LOWS

Standardized anomalies of SST/SIC using ERAIERAI database, resolution 0.75°x0.75°Anomaly = (SST (/SIC) March 2007(/2013) - mean SST (/SIC) March 79-13)/ standard deviation

February 2007 February 2013

Observations :• 0 PL in March

2007• 13 PL in March

2013

Why this difference?

Analysis of SST/SIC in February

Strong negative anomaly of SIC in February 2013Positive SST anomalies predominant

INFLUENCE OF WINTER SEA ICE ON POLAR LOWS

March 2007 March 2013

SST :•Strong positive anomalies in March 2007 •Colder SST in March 2013 than in February due to several cold air outbreaks

SIC :•Negative SIC anomaly stronger in March 2007 than in February•Formation of sea ice between February and March 2013 over the Barents Sea likely due to several cold air outbreaks

Standard anomalies of SST/SIC using ERAIERAI database, resolution 0.75°x0.75°Anomaly = (SST (/SIC) March 2007(/2013) - mean SST (/SIC) March 79-13)/ standard deviation

SST

SIC

MSLP 12-17 JANUARY 2009

ATMOSPHERIC SITUATION IN 16 JANUARY 2009

PV 300 ERAI FROM 9 TO 19 JANUARY 2009

MONTHLY ANOMALIES OF SST BETWEEN 2013 & 2007 USING OISST

SST Jan 2013 - SST Jan 2007

SST Feb 2013- SST Feb 2007

SST Mar 2013- SST Mar 2007

SST Apr 2013 - SST Apr 2007

Use of OISST database, monthly data, resolution 1°x1°, since 1982

January and February 2013 : SST warmer

March and April 2013 : SST colder

MONTHLY ANOMALIES OF SIC BETWEEN 2013 & 2007 USING OISST

SIC Jan 2013 - SIC Jan 2007

SIC Feb 2013 - SIC Feb 2007

SIC Mar 2013 - SIC Mar 2007

SIC Apr 2013 - SIC Apr 2007

January and February 2013 : less SIC around Svalbard and at West of Novaya Zemlya

March and April 2013 : more SIC at North and East of Barents Sea

ATMOSPHERIC SITUATION IN MARCH 2007

PV 300hPaERAI

SST-T500ERAI

LHF NCEP SHF NCEP

Wind 925 hPa ERAI

Warm winds ~ 270 K from SW prevent the development of PLNo stratospheric intrusion that could trigger PL developmentLow SST-T500 < 37 K (indicator of convective tropospheric heating driven by surface fluxes/static stability)Weak turbulent flux : LHF < 90 W.m-2, SHF ~ 50 W.m-2

T (K)

ATMOSPHERIC SITUATION IN MARCH 2013

PV 300hPaERAI

SST-T500ERAI

LHF NCEP

SHF NCEP

Cold winds ~ 255 K from NE allow formation of sea ice at North and East of BarentsStrong signature of PV anomaly > 50 pvu at SE of BarentsStrong SST-T500 > 47 K at North of Norway, where PL formWeak turbulent flux : LHF > 115 W.m-2, SHF ~ 250 W.m-2

Wind 925 hPa ERAI

T (K)

• Analysis of several cases of long duration Polar Lows : 2008-04-04, 2012-04-04, 2012-02-21

• Study of SST, SIC and atmospheric parameters• Exceptional case in Kara Sea in 2009-01-16

CASE STUDY OF SEVERAL POLAR LOWS

DECEMBER SEA ICE EXTENT OVER THE BARENTS SEA

Large Interannual variability

INFLUENCE OF SUMMER SEA ICE EXTENT DETREND

In December

SST-T 500 hPa

Z 500 hPa

PV 300 hPa

Winds 925 hPa

INFLUENCE OF SUMMER SEA ICE EXTENT DETREND

In January

SST-T 500 hPa

Z 500 hPa

PV 300 hPa

Winds 925 hPa

•The research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013), under grant agreement n.308299•NACLIM www.naclim.eu