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Marine Stratus and Its Relationship to Regional and Large-Scale Circulations: An Examination with the NCEP CFS Simulations P. Xie 1) , W. Wang 1) , W. Higgins 1) , and P.A. Arkin 2) 1) NOAA Climate Prediction Center 2) ESSIC, Univ. of Maryland. Objectives:.

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Marine Stratus and Its Relationship to Regional and Large-Scale Circulations:An Examination with the NCEP CFS SimulationsP. Xie1), W. Wang1), W. Higgins1), and P.A. Arkin2)1) NOAA Climate Prediction Center2) ESSIC, Univ. of Maryland

  • To examine the CFS model bias associated with the insufficiently simulated marine stratus clouds over SE Pacific and SE Atlantic;
  • To investigate the atmospheric circulation involving the formation and variations of the marine stratus clouds;
two sets of cfs simulations examined
Two Sets of CFS Simulations Examined
  • CFS AMIP Simulations [GFS]
    • The atmospheric component of the CFS model (GFS03) is forced by observed oceanic condition;
    • 1979 – 2003;
  • CFS CMIP Simulations [CFS]
    • The GFS03 atmospheric model is fully coupled with an OGCM (MOM3) ;
    • 4 sets of CMIP simulations for a 32-year period each
annual mean precipitation
Annual Mean Precipitation
  • Large-scale precipitation patterns reproduced reasonably well;
  • Differences exist in the magnitude of precipitation and in the latitudinal position of the ITCZ;
annual cycle of the atlantic itcz
Annual Cycle of the Atlantic ITCZ
  • GFS simulates annual cycle pretty well, with excessive precipitation;
  • The Atlantic ITCZ located too south during DJF and MAM in the CFS simulation;
annual cycle of e pacific itcz
Annual Cycle of E. Pacific ITCZ
  • Relatively good reproduction of precipitation fields by GFS;
  • ITCZ too strong and located a little bit too south during DJF and MAM in the CFS;
annual mean sst surf wind
Annual MeanSST / Surf. Wind
  • Warm SST bias in the CFS over the southeast Atlantic and southeast Pacific;
  • Surface wind bias over the regions of warm SST bias.
possible causes for the warm sst bias over the regions
Possible Causes for the Warm SST Bias over the Regions

1. Insufficient vertical transportation

 oceanic observations

(will not check this time)

2. Enhanced heat transport through advection

 surface wind speed

3. Reduced evaporation

 Surface wind speed

4. Excessive incoming solar radiation

 cloudiness

annual mean total cloud
Annual MeanTotal Cloud (%)
  • In general, CFS cloud amount is smaller than that of observations almost everywhere;
  • Insufficient amount of clouds simulated by the CFS over the regions with warm SST bias;
cloudiness in other ncep products
Cloudiness in other NCEP Products
  • Only CDAS1 reproduced the cloudiness (mostly low clouds) reasonably well;
  • CDAS2, GFS and CFS failed to generate cloud amounts over the regions;
annual mean sw radiation
Annual MeanSW Radiation
  • Excessive incoming solar radiation over both the SE Atlantic and SE Pacific;
  • Differences of over 50W/m2 over SE Pacific;
comparison with epic buoy data at 20 o s 85 o w
Comparison with EPIC Buoy Data at [20oS,85oW]
  • Close agreements between buoy and satellite observations;
  • Warm SST bias of ~2oC and positive SW radiation of ~50W/m2 in CFS compared to the EPIC buoy observations;
cloud picture over se pacific from fig 3 of bretherton et al 2004
Cloud Picture over SE Pacific [from fig.3 of Bretherton et al. (2004)]
  • Scattered stratus clouds over the regions;
vertical profiles of boundary layer from fig 10 of bretherton et al 2004
Vertical Profiles of Boundary Layer [from fig.10 of Bretherton et al. (2004)]
  • Well mixed boundary layer of 1-1.5 km capped by inversion;
  • Stratus cloud layer of ~500m atop the boundary layer;

Liquid Water

Water Vapor


diurnal cycle in isccp cloudiness
Diurnal Cycle in ISCCP cloudiness
  • 24-hour mean cloudiness (top) shows a bi-polar structure over the dry zone and nearby continent, suggesting a diurnal cycle cell caused by sea breeze;
  • 3-hourly ISCCP cloud data (bottom) presents distinct diurnal cycles of different phases over the dry zone and the land area;
diurnal cycle in circulation from cdas1
Diurnal Cycle in circulation from CDAS1


  • 24-hourly mean removed to examine the diurnal cycle;
  • Cells of regional circulations involving land-sea contrasts;
  • Overall good performance of CFS model in reproducing large-scale precipitation patterns;
  • Merdional shifts of ITCZ over Eastern Pacific and Atlantic sectors;
  • The displacements of the ITCZ closely related to the warm SST bias in the SE Atlantic and SE Pacific stratus deck regions;
  • The warm SST bias caused largely by insufficiently simulated stratus clouds; and
  • Strong diurnal cycle in the stratus clouds generated by regional circulation caused by land-sea contrasts between the oceanic regions and their adjacent continents.
annual mean surface wind
Annual MeanSurface Wind
  • Small differences in surface wind speed between the CFS model and observations (QuikScatter) Over the SE Atlantic and SE Pacific;