the hadley centre
DESCRIPTION
The Hadley Centre. The forcing of sea ice characteristics by the NAO in HadGEM1 UK Sea Ice Workshop, 9 September 2005 Chris Durman 1,2 and Jonathan Bamber 2 1. Hadley Centre for Climate Prediction and Research, Met Office 2. Bristol Glaciology Centre, School of Geographical Sciences, - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/1.jpg)
© Crown copyright 2004 Page 1
The Hadley Centre
The forcing of sea ice characteristics by the NAO in HadGEM1
UK Sea Ice Workshop, 9 September 2005
Chris Durman1,2 and Jonathan Bamber2
1. Hadley Centre for Climate Prediction and Research, Met Office
2. Bristol Glaciology Centre, School of Geographical Sciences,University of Bristol
With thanks to: Tim Johns, Ann Keen, Alison McLaren and Jeff Ridley.
![Page 2: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/2.jpg)
© Crown copyright 2004 Page 2
The Hadley Centre
Talk Outline
1. Introduction
2. Simulated NAO and climate response in comparison with observations
3. Mechanisms of ice response:• Beaufort Sea / East Arctic Basin• Labrador Sea
4. Conclusions
![Page 3: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/3.jpg)
© Crown copyright 2004 Page 3
The Hadley Centre
The NAO and Arctic Sea Ice
• NAO dominant mode of atmospheric variability in the North Atlantic region (Hurrell, 1995).
• “See-saw” of intensification and weakening in PMSL between Azores High and Icelandic Low centres of action.
• NAO “high +ve state” when pressure gradient is at a maximum.
• Over the Arctic, modified circulation patterns result in perturbed geostrophic wind forcing → drives surface temperature changes.
• Correlation between geostrophic winds and ice motion can be as high as 0.8 in the central Arctic (e.g. Thomas, 1999).
• Perturbed surface temperatures influence the rate at which ice grows / melts thermodynamically.
![Page 4: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/4.jpg)
© Crown copyright 2004 Page 4
The Hadley Centre
Experimental setup and data
HadGEM1 IPCC AR4 Control run:
• Fixed 1860 forcing levels for greenhouse gases, ozone, sulphur, other precursor emissions and land surface conditions.
• Spinup integration of 85 years in length was carried out from which the controlrun was initialised.
• Spinup ocean state initialised from September climatology of Levitus.
• Spinup Northern Hemisphere sea ice volume initialised from HadISST.
Data:
• First 300 years of control run analysed here.
![Page 5: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/5.jpg)
© Crown copyright 2004 Page 5
The Hadley Centre
DJF PMSL
![Page 6: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/6.jpg)
© Crown copyright 2004 Page 6
The Hadley Centre
DJF PMSL
![Page 7: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/7.jpg)
© Crown copyright 2004 Page 7
The Hadley Centre
Leading order EOFs of DJF PMSL
Variance: 44.8% Variance: 41.1%
![Page 8: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/8.jpg)
© Crown copyright 2004 Page 8
The Hadley Centre
HadGEM1 NAO Index
Index: Difference in PMSLbetween Azores and Iceland.
Normalisation: subtract meanand divide by standard deviation.
Define “High NAO Years” asthose where normalisedIndex exceeds unity.
300 year control run yields48 High NAO Years.
![Page 9: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/9.jpg)
© Crown copyright 2004 Page 9
The Hadley Centre
HadGEM1 DJF PMSL
![Page 10: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/10.jpg)
© Crown copyright 2004 Page 10
The Hadley Centre
DJF Surface Temperature Anomaly
DJF Ice Concentration Anomaly
![Page 11: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/11.jpg)
© Crown copyright 2004 Page 11
The Hadley Centre
HadGEM1 DJF Ice Property Anomalies
![Page 12: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/12.jpg)
© Crown copyright 2004 Page 12
The Hadley Centre
HadGEM1 DJF ice velocity
![Page 13: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/13.jpg)
© Crown copyright 2004 Page 13
The Hadley Centre
HadGEM1 DJF Wind Velocity
![Page 14: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/14.jpg)
© Crown copyright 2004 Page 14
The Hadley Centre
JJA Ice Response
Concentration Thickness
![Page 15: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/15.jpg)
© Crown copyright 2004 Page 15
The Hadley Centre
Ice volume flux (m3 per season) through longitude180oW averaged between 70oN and 80oN
0
1E+11
2E+11
3E+11
4E+11
5E+11
6E+11
7E+11
8E+11
9E+11
DJF* MAM JJA SON
Climatology
NAO+
![Page 16: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/16.jpg)
© Crown copyright 2004 Page 16
The Hadley Centre
DJF Labrador Sea Ice Anomalies
![Page 17: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/17.jpg)
© Crown copyright 2004 Page 17
The Hadley Centre
DJF Labrador Sea Anomalies
![Page 18: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/18.jpg)
© Crown copyright 2004 Page 18
The Hadley Centre
Implied DJF ice thickness response in the Labrador Sea
Average increase in rate of change of ice thickness due to thermodynamic processes = +2.07x10-8 ms-1.
=> anomalous thickness of 0.16m compared with model climatology.
But average thickness anomaly = 0.086m.
Thermodynamics not the whole story?
![Page 19: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/19.jpg)
© Crown copyright 2004 Page 19
The Hadley Centre
DJF ice thermodynamics and velocity
![Page 20: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/20.jpg)
© Crown copyright 2004 Page 20
The Hadley Centre
HadGEM1 DJF PMSL
![Page 21: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/21.jpg)
© Crown copyright 2004 Page 21
The Hadley Centre
Conclusions
• HadGEM1 realistically simulates the NAO dipole pressure pattern.
• Simulated HadGEM1 surface temperature and Arctic sea ice concentrationanomaly patterns associated with the NAO are consistent with observations.
• The response of Arctic basin sea ice to high NAO events is a dipole with increased ice in the western Arctic and reduced ice in the east. This pattern is formed as a result of reduced ice transport due to perturbed wind forcing.
• Ice thickness anomalies in the Labrador Sea are largely initiated by thermodynamic processes but dynamic processes act to limit the anomalies.
![Page 22: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/22.jpg)
© Crown copyright 2004 Page 22
The Hadley Centre
Extra slides
![Page 23: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/23.jpg)
© Crown copyright 2004 Page 23
The Hadley Centre
Fram Strait ice export response
![Page 24: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/24.jpg)
© Crown copyright 2004 Page 24
The Hadley Centre
Fram Strait export response?
(Zhang et al., 2000, J. Climate)
![Page 25: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/25.jpg)
© Crown copyright 2004 Page 25
The Hadley Centre
HadGEM1 normalised NAO index vs average Fram Strait ice export
Corr = 0.03
![Page 26: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/26.jpg)
© Crown copyright 2004 Page 26
The Hadley Centre
HadGEM1 DJF Wind Velocity
![Page 27: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/27.jpg)
© Crown copyright 2004 Page 27
The Hadley Centre
Running 7-year means of simulated normalised NAO index
![Page 28: The Hadley Centre](https://reader035.vdocuments.us/reader035/viewer/2022062309/568159e9550346895dc7371a/html5/thumbnails/28.jpg)
© Crown copyright 2004 Page 28
The Hadley Centre
(Ringer et al., 2005, J. Climate)