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Sensitivity of atmospheric near-land temperature in Europe to SST

Sensitivity of atmospheric near-land temperature in Europe to SST . Andrey Vlasenko , Armin Köhl, Detlef Stammer. Institut für Meerskunde Universität Hamburg Hamburg. TASK. Task 1.2.1 Identification of the atmospheric response to ocean surface state changes

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Sensitivity of atmospheric near-land temperature in Europe to SST

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  1. Sensitivity of atmospheric near-land temperature in Europe to SST Andrey Vlasenko, Armin Köhl, Detlef Stammer Institut für MeerskundeUniversität HamburgHamburg

  2. TASK Task 1.2.1 Identification of the atmospheric response to ocean surface state changes The EU FP7 THOR adjoint assimilation system will be used 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 SST, sea surface salinity or sea ice thickness and concentration. The sensitivity information will be used subsequently to unravel the processes affecting the important climate parameters over northern Europe and underlying time scales Task leading to deliverable D18.

  3. Plan of the Experiment • Spin up the climate model CESAM, until the proper climatology is established • Develop such cost functional that • measures the atmospheric near-land temperature in Europe • gives the gradient with minimum numerical noise during the adjoin computations • Using TAF AD tool, obtain the adjoint of CESAM • Develop a set of filters that remove numerical noise without spoiling the result

  4. The Model CESAM = PLASIM(atmosphere) + MITgcm(ocean) CESAM Initialize Atmosphere and Ocean The Driver Program The Main Loop Interpolator MITgcm ocean(1 step) PLASIM Atmosphere (10 steps) Interpolator Postprocessiong RESULT

  5. The Experiment • SETUP: • Grid resolution • In atmosphere is T21 with 10 vertical layers • in ocean is with 15 vertical layers. • Time step: in ocean is equal to 8 hours in atmosphere is equal to 48 minutes. • TASK: • Compute • 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 𝐽 (adjoint of CESAM) was generated by a special algorithmic differentiation tool TAF.

  6. Problem 1 The unstable mode.

  7. Problem 2 Distribution of the interpolation error, appearing during coupling

  8. Problem 3 Distribution of the values of adjoit of SST represented as histogram

  9. Solutions • Implementation of a cascade filtering: • Low-pass filter. An unstable mode, resulting in exponential increase of high frequency, appears during estimation of adjoints. This mode can be removed without affecting the data by applying low pass filter. • Grid noise removal filter. The noise appears due to truncation/approximation errors in the coupling routine. The pattern of these errors are almost constant in space and timeand therefore can be easily recognized and subtracted from the data. • Histogram filter. As above, due to errors on the coupling stage a couple of outliers appear near the sharp boundaries of the continents. The magnitude of outliers are several order bigger than the magnitude of the data. Therefore, they can be easily designated and removed by a histogram filter.

  10. Results Sensitivity of near surface atmospheric temperature on 15-th of February in Northern Europe to SST 16 hours before the end of the target period.

  11. Results Sensitivity of near surface atmospheric temperature on 15-th of February in Northern Europe to SST 48 hours before the end of the target period.

  12. 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.

  13. Results Sensitivity of near surface atmospheric temperature on 15-th of February in Northern Europe to SST 150 hours before the end of the target period.

  14. 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 on short time scales of about 1 day mainly kinematically via heating or cooling the air temperature above. 3. On longer time scales of about a few days, dynamic effects become more relevant. 4. Optimal patterns resemble the regression patterns SST/NAO, suggesting that SST most efficiently affects the atmospheric circulation by triggering an NAO type response.

  15. Further Development • To obtain the atmospheric response to SST in a framework of maximum configuration where all processes associated with moisture are included. • To estimate the atmospheric sensitivity to other oceanic and atmospheric state variables particularly geopotential height and surface pressure.

  16. Thank you

  17. 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

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