# Presentation: 199046

## Marine Stratus and Its Relationship to Regional and Large-Scale Circulations:An Examination with the NCEP CFS SimulationsP. Xie1), W. Wang1), W. Higgins1), and P.A. Arkin2)1)  NOAA Climate Prediction Center2)  ESSIC, Univ. of Maryland

## Objectives:

- 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;

**Notes:**
CDAS = NCEP/NCAR reanalysis

## 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 

- 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 

- 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 

- 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

- 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

- 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 (%)

- 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

- 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

- 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 [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)] 

- Scattered stratus clouds over the regions;

## 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**

**Temperature**

## 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 CDAS1 Cloudiness 

## Diurnal Cycle in circulation from CDAS1

- 24-hourly mean removed to examine the diurnal cycle;
- Cells of regional circulations involving land-sea contrasts;

**06Z**

## Summary 

- 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

- Small differences in surface wind speed between the CFS model and observations (QuikScatter) Over the SE Atlantic and SE Pacific;