Research Articles

Validation of remote sensing and weather model forecasts in the Agulhas ocean area to 57°S by ship observations

Christophe Messager, Vincent Faure
South African Journal of Science | Vol 108, No 3/4 | a735 | DOI: https://doi.org/10.4102/sajs.v108i3/4.735 | © 2012 Christophe Messager, Vincent Faure | This work is licensed under CC Attribution 4.0
Submitted: 05 May 2011 | Published: 09 March 2012

About the author(s)

Christophe Messager, Laboratoire de Physique des Océans, France
Vincent Faure, Japan Agency for Marine-Earth Science and Technology, Japan


Share this article

Bookmark and Share

Abstract

The region south of South Africa, encompassing the Agulhas Current and Retroflection, and part of the Southern Ocean, is known for its severe meteorological conditions. Because of these conditions, in-situ observations are rare. Consequently, remote-sensing satellite observations and high-resolution regional weather forecasts at the ocean surface are difficult to assess. However, atmospheric data collected in the southern hemisphere summer of 2008 during the International Polar Year-BONUS-GoodHope campaign were used to validate two satellite data sets: the twice daily QuikSCAT winds and the daily OAflux data set of latent and sensible heat fluxes. The surface winds and heat fluxes forecasts produced by a regional atmospheric model were also assessed along the ship track. In this study, we have shown that the two data sets exhibited a very good accordance with daily in-situ observations. During the campaign, the correlation coefficients for wind speed and direction were 0.97 and 0.91, respectively, and those for latent and sensible heat fluxes were 0.92 and 0.90, respectively. The QuikSCAT wind speed was underestimated by 1.37 m/s relative to in-situ data, south of the Subtropical Front. Large differences in heat fluxes in both OAflux and the atmospheric model were observed when crossing the Subtropical Front and a warm eddy, as well as during a storm, when gale force winds reached more than 20 m/s. The two data sets were then used to assess the regional model forecasts over a larger area south of South Africa, not limited to the ship track. Most of the model errors were located in a region north of the Subtropical Front, where the sea surface temperature used by the model was not accurate enough to reproduce the relevant mesoscale oceanic features driving the spatial variability of the surface winds and heat fluxes. Finally, compared to in-situ and remote sensing observations, the numerical modelling weather forecast produced realistic atmospheric conditions over the sea south of the Subtropical Front.

Keywords

numerical weather forecast; Agulhas Retroflection; air–sea fluxes; ocean wind; remote sensing

Metrics

Total abstract views: 999
Total article views: 1695

References


Bryden HL, Beal LM, Duncan LM. Structure and transport of the Agulhas Current and its temporal variability.J Oceanogr. 2005;61:479–492. http://dx.doi.org/10.1007/s10872-005-0057-8

Lutjeharms JRE, Van Ballegooyen RC. The retroflexion of the Agulhas Current. J Phys Ocean. 1988;18:1570–1583.

Boebel O, Lutjeharms J, Schmid C, Zenke W, Rossby T, Barron C. The Cape Cauldron: A regime of turbulent inter-ocean exchange. Deep Sea Research II. 2003;50:57–86. http://dx.doi.org/10.1016/S0967-0645(02)00379-X

Lutjeharms JRE. The Agulhas Current. Heidelberg: Springer-Verlag; 2006.

Jury MR, Walker N. Marine boundary layer modification across the edge of the Agulhas Current. J Geophys. Res1988;93:647–654. http://dx.doi.org/10.1029/JC093iC01p00647

Lee-Thorp AM, Rouault M, Lutjeharms JRE. Moisture uptake in the boundary layer above the Agulhas Current: A case study. J Geophys Res. 1999;104:1423–1430. http://dx.doi.org/10.1029/98JC02375

Rouault M, Lutjeharms JRE. Air–sea exchanges over an Agulhas eddy at the subtropical convergence. Global Atmos–Ocean Syst. 2000;7:125–150.

O’Neill L, Chelton D, Esbensen S, Wentz F. High-resolution satellite measurements of the atmospheric boundary layer response to SST variations along the Agulhas Return Current. J Climate. 2005;18:2706–2723. http://dx.doi.org/10.1175/JCLI3415.1

Small RJ, DeSzoeke SP, Xie SP, et al. Air–sea interaction over ocean fronts and eddies. Dyn Atmos Oceans. 2008;45:274–319. http://dx.doi.org/10.1016/j.dynatmoce.2008.01.001

Faure V, Arhan M, Speich S, Gladyshev S. Heat budget of the surface mixed layer south of Africa. Ocean Dynamics. 2011;61(10):1441–1458. http://dx.doi.org/10.1007/s10236-011-0444-1

Orsi AH, Whitworth III T, Nowlin WD. On the meridional extent and fronts of the Antarctic Circumpolar Current. Deep Sea Research I. 1995;42:641–673. http://dx.doi.org/10.1016/0967-0637(95)00021-W

Belkin IM, Gordon AL. Southern Ocean fronts from the Greenwich meridian to Tasmania. J Geophys Res. 1996;101:3675–3696. http://dx.doi.org/10.1029/95JC02750

Dencausse G, Arhan M, Speich S. Spatio-temporal characteristics of the Agulhas Current Retroflection. Deep Sea Research I. 2010;57(11):1392–1405. http://dx.doi.org/10.1016/j.dsr.2010.07.004

Arhan M, Speich S, Messager C, Dencausse G, Fine R, Boyé M. Anticyclonic and cyclonic eddies of subtropical origin in the subantarctic zone south of Africa. J Geo Res. 2011;116:C11004. http://dx.doi.org/10.1029/2011JC007140

Ricciardulli L, Wentz F. Reprocessed QuikSCAT (V04) wind vectors with Ku-2011 geophysical model function. Remote Sensing Systems Technical Report 043011. Santa Rosa, CA: Remote Sensing Systems; 2011.

Remote Sensing Systems. Version-4 QuikSCAT Ocean Surface Wind Vectors [homepage on the Internet]. c2011 [updated 2011 June 29; cited 2011 Dec 12]. Available from: http://www.remss.com

Fairall CW, Bradley EF, Hare JE, Grachev AA, Edson JB. Bulk parameterization on air–sea fluxes: Updates and verification for the COARE algorithm. J Climate. 2003;16:571–591. http://dx.doi.org/10.1175/1520-0442(2003)016<0571:BPOASF>2.0.CO;2

Woods Hole Oceanographic Institution. Objectively Analyzed Air–sea Fluxes (OAflux) for the global oceans, a project funded by the NOAA Climate Observations and Monitoring (COM) program [homepage on the Internet]. c2008 [updated 2011 Nov 03; cited 2011 Dec 12]. Available from: http://oaflux.whoi.edu/

Skamarock WC, Klemp JB, Dudhia J, et al. A description of the Advanced Research WRF Version 3. NCAR Technical Note 2008 NCAR/TN–475+STR [document on the Internet]. c2008 [updated 2008 June 01; cited 2011 Dec 12]. Available from: http://www.mmm.ucar.edu/wrf/users/docs/arw_v3.pdf

Yueh SH, Wilson WJ, Dinardo SJ, Li FK. Polarimetric microwave brightness signatures of ocean wind directions. IEEE Trans Geosci Remote Sensing. 1999;37(2):949–959. http://dx.doi.org/10.1109/36.752213

LaCasse KM, Splitt ME, Lazarus SM, Lapenta WM. The impact of high resolution sea surface temperatures on short-term model simulations of the nocturnal Florida marine boundary layer. Mon Wea Rev. 2008;136(4):1349–1372. http://dx.doi.org/10.1175/2007MWR2167.1

Song Q, Chelton DB, Esbensen SK, Thum N, O’Neill LW. Coupling between sea surface temperature and low-level winds in mesoscale numerical models. J Climate. 2009;22:146–164. http://dx.doi.org/10.1175/2008JCLI2488.1

O’Neill L, Esbensen S, Thum N, Samelson R, Chelton D. Dynamical analysis of the boundary layer and surface wind responses to mesoscale SST perturbations. J Climate. 2010;23:559–581. http://dx.doi.org/10.1175/2009JCLI2662.1

Chelton DB, Schlax MG, Samelson RM. Summertime coupling between sea surface temperature and wind stress in the California Current System. J Phys Oceano. 2007;37(3):495–517. http://dx.doi.org/10.1175/JPO3025.1

Case JL, Crosson WL, Kumar SV, Lapenta WM, Peters-Lidard CD. Impacts of high-resolution land surface initialization on regional sensible weather forecasts from the WRF model. J Hydrometeor. 2008;9:1249–1266. http://dx.doi.org/10.1175/2008JHM990.1

Zeng X, Beljaars A. A prognostic scheme of sea surface skin temperature for modeling and data assimilation. Geophys Res Lett. 2005;32:L14605. http://dx.doi.org/10.1029/2005GL023030



Reader Comments

Before posting a comment, read our privacy policy.

Post a comment (login required)

Crossref Citations

No related citations found.