We use the surface energy budget for South Pole, Antarctica derived from routine radiation and meteorological observations for the time period 1994-2000 to evaluate the Modele Atmospherique Regional (MAR) and ERA-40 over the Antarctic plateau. We find biases in individual components of the energy budgets of both models that often compensate for each other. The biases are primarily due to parameterizations of surface albedo, cloud cover, and boundary layer parameterizations. The timing of synoptic events is generally found to be in error in both models. However, MAR has greater skill than ERA-40 in simulating the frequency and magnitude of mesoscale weather over the South Pole. The influence of different source regions on accumulation in MAR is assessed through objective cluster analysis for the seven-year period. An intercomparison of the surface energy budget over the South Pole between observations, ERA-40, and the Modèle Atmosphérique Régional M. Town 1 , I. Gorodetskaya 2 , H. Gallée 3 , V. P. Walden 4 , C. Genthon 3 Time series Conclusions Altitude = 2835 m; Accumulation rate = 8 cm/yr; Mean temperature = -50 o C Seasonal cycle = -58 o C to -28 o C Winter T range = -80 o C to -40 o C Figure 1. There are two surface weather regimes at the South Pole (warm/windy and cold/calm). Abstract South Pole MAR is able to simulate synoptic variance better than ERA-40, but neither product can simulate synoptic timing. MAR is missing cloud cover during summer, causing low bias in LWD annual cycle. T is simulated well, but possibly due to tuning of LWD to other observations in the Antarctic interior. 1 Seattle University, Seattle WA USA ([email protected]) 2 Department of Earth and Env Sciences, Katholieke Universiteit Leuven, Belgium 3 LGGE/CNRS, Grenoble, France 4 Department of Geography, University of Idaho, Moscow, ID USA Acknowledgements: D. Winebrenner provided the wavelet software and advice on wavelets. S. Warren and V. P. Walden provided invaluable advice. T. Mefford and E. Dutton of NOAA GMD supplied the South Pole data set. This work was funded in part by the U.S. National Science Foundation OPP-0540090, and by Agence Nationale de la Recherche (France) grant OTP 232333. Figure 2. Case-study of 2-m T for early 1995. Figure 3. Scatter plot of 2-m T for 1994-2000. Spectral Analysis Figure 4. Wavelet power spectra of (a) 2-m T and (b) wind speed for 1994-2000. Figure 5. Wavelet power spectra of (a) longwave downwelling fluxes and (b) shortwave downwelling fluxes for 1994-2000. Cloud cover d. cloud fraction Figure 6. Time series (a)-(c) show monthly means of 2-m T of all-sky, clear-sky, and all-sky minus clear- sky for 1994-2000. Time series (d) shows monthly means of cloud fraction for 1994-2000. Table 1. Compensating biases in seasonal components of the surface energy budget over the South Pole NW warm adv 30% accum SW warm adv 33% accum cold/calm 5% accum Why is it important? Synoptic events determine most of accumulation at the South Pole...! Accumulation percentage as simulated by MAR (1994-2000, excluding summer Jan-Feb, regimes determined by cluster analysis based on 12 variables): warm NW advection: 30% warm SW advection: 33% high stratospheric clouds: 19% cold: 5% transitional: 8%

M. Town 1 , I. Gorodetskaya 2 , H. Gall ée 3 , V. P. Walden 4 , C. Genthon 3

Download PPT Report

Upload
barrett-edwards
View
20
Download
0

Tags:

Embed Size (px)

DESCRIPTION

South Pole. Spectral Analysis. Why is it important?. Abstract. Cloud cover. Time series. Conclusions. Table 1. Compensating biases in seasonal components of the surface energy budget over the South Pole. - PowerPoint PPT Presentation

Citation preview

An intercomparison of the surface energy budget over the South Pole between observations, ERA-40, and the Modèle Atmosphérique Régional

M. Town1, I. Gorodetskaya2, H. Gallée3, V. P. Walden4, C. Genthon3

Time series

Conclusions

Altitude = 2835 m; Accumulation rate = 8 cm/yr; Mean temperature = -50oCSeasonal cycle = -58oC to -28oCWinter T range = -80oC to -40oC

Figure 1. There are two surface weather regimes at the South Pole (warm/windy and cold/calm).

Abstract

South Pole

MAR is able to simulate synoptic variance better than ERA-40, but neither product can simulate synoptic timing.

MAR is missing cloud cover during summer, causing low bias in LWD annual cycle.

T is simulated well, but possibly due to tuning of LWD to other observations in the Antarctic interior.

1Seattle University, Seattle WA USA ([email protected])2Department of Earth and Env Sciences, Katholieke Universiteit Leuven, Belgium3LGGE/CNRS, Grenoble, France4Department of Geography, University of Idaho, Moscow, ID USA

Acknowledgements: D. Winebrenner provided the wavelet software and advice on wavelets. S. Warren and V. P. Walden provided invaluable advice. T. Mefford and E. Dutton of NOAA GMD supplied the South Pole data set. This work was funded in part by the U.S. National Science Foundation OPP-0540090, and by Agence Nationale de la Recherche (France) grant OTP 232333.

Figure 2. Case-study of 2-m T for early 1995. Figure 3. Scatter plot of 2-m T for 1994-2000.

Spectral Analysis

Figure 4. Wavelet power spectra of (a) 2-m T and (b) wind speed for 1994-2000.

Figure 5. Wavelet power spectra of (a) longwave downwelling fluxes and (b) shortwave downwelling fluxes for 1994-2000.

Cloud cover

d. cloud fraction

Figure 6. Time series (a)-(c) show monthly means of 2-m T of all-sky, clear-sky, and all-sky minus clear-sky for 1994-2000. Time series (d) shows monthly means of cloud fraction for 1994-2000.

Table 1. Compensating biases in seasonal components of the surface energy budget over the South Pole

NW warm adv30% accum

SW warm adv33% accum

cold/calm5% accum

Why is it important?

Synoptic events determine most of accumulation at the South Pole...!

Accumulation percentage as simulated by MAR (1994-2000, excluding summer Jan-Feb, regimes determined by cluster analysis based on 12 variables):

warm NW advection: 30% warm SW advection: 33% high stratospheric clouds: 19% cold: 5% transitional: 8%