Sensitivity of atmospheric near-land temperature in Northern Europe to SST

Andrey Vlasenko, Armin Köhl, Detlef Stammer

University Hamburg

Goals

To identify sensitivities of predictable elements over northern Europe, such as air temperature or precipitation, on parameters in the North Atlantic and the Arctic, such as

1. ) SST done 2. ) sea surface salinity to be done 3. ) sea ice thickness and concentration to be done

The Model

CESAM = PLASIM(atmosphere) + MITgcm(ocean).

The Driver Program

CESAM

Initialize Atmosphere and Ocean

The Main Loop

Postprocessiong

Interpolator

RESULT

MITgcm ocean(1 step)

PLASIM Atmosphere (10 steps)Interpolator

The Adjoint Model

TAF AD(CESAM) = CESAM AD*

* S. Blessing, T. Kaminski, F. Lunkeit, I. Matei, R. Giering, A. Köhl, M. Scholze, K. Fraedrich, and D. Stammer. Testing variational estimation of process parameters and initial conditions of an Earth System Model. TellusA, 2014

The adjoint model was obtained as a result of collaboration of Fastopt and University of Hamburg.

Plan of the Experiment 1. Spin up the climate model CESAM, until the proper climatology is established

2. Develop such cost functional that

a) measures the atmospheric near-land temperature in Europe

b) gives the gradient with minimum numerical noise during the adjoin computations

3. Using TAF AD tool, obtain the adjoint of CESAM

4. Investigate the dependence of the sensitivity with respect to NAO phase

The ExperimentSETUP: 1. Grid resolution

a) In atmosphere is T21 with 10 vertical layersb) in ocean is with 15 vertical layers.

2. Time step: in ocean is equal to 8 hours in atmosphere is equal to 48 minutes.

TASK: Compute , where is the near land temperature in northern Europe

Cost Functional:

Where , is temperature, is spatial coordinate, time steps, is a point in the middle of Europe, has a value that temperature values outside Europe have negligible impact in .

Adjoint:The gradient of (adjoint of CESAM) was generated by a special algorithmic differentiation tool TAF. 𝐽

Results 1. Near land temperature sensitivity to SST, negative NAO 2. Near land temperature sensitivity to SST, positive NAO

1

2

Results1. Near land temperature (NLT) sensitivity to SST, negative NAO

.

Sensitivity of NLT to SST after 24 h, NAO-

Sensitivity of NLT to SST after 48 h, NAO-

Sensitivity of NLT to SST after 62 h, NAO-

Sensitivity of NLT to SST after 100 h, NAO-

Results2. NLT sensitivity to SST, NAO+

Sensitivity of NLT to SST after 24 h, NAO+

Sensitivity of NLT to SST after 48 h, NAO+

Sensitivity of NLT to SST after 62 h, NAO+

Sensitivity of NLT to SST after 100 h, NAO+

Results Contribution of sensible heat fraction in sensitivity of NLT to SST

Sensible heat fraction after 24 h, NAO+

Sensible heat fraction after 48 h, NAO+

Sensible heat fraction after 62 h, NAO+

Sensible heat fraction after 100 h, NAO+

Comparison with the results of A. Czasa and C Frankignoul*

SST regression maps showing the tripole (in K, gray shading, dashed contours for negative) and the North Atlantic horseshoe patterns (thick contours, every 0.1 K, dashed for negative).

* A. Czasa and C Frankignoul: Observed Impact of Atlantic SST Anomalies on the North Atlantic Oscillation . J. Cli. (15) 2002.

Conclusions

1. The sensitivity of atmosphere to SST in a framework of Coupled model can be estimated.

2. It was shown that SST affects the atmosphere in Europe mainly via changes in flux of

latent heat.

3. Correlation between

a. complete sensitivity patterns, obtained for negative and positive NAO equals 0.63

b. Sensitive heat fraction, obtained for negative and positive NAO equals 0.74

4. It was shown that sensitivity pattern is dependent on pressure fluctuations.

5. Optimal patterns resemble the regression patterns SST/NAO, suggesting that SST most

efficiently affects the atmospheric circulation by triggering an NAO type response.

Thank you

•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