Testing of the Zeng and Beljaars scheme in the TWP Michael Brunke and Xubin Zeng Department of Atmospheric Sciences The University of Arizona Tucson, Arizona USA

Motivation  The effect of the diurnal cycle on the calculation of surface fluxes.  Brunke et al. (2011) compared an example of flux diurnal cycles to those of ship obs. (Brunke et al. 2011)

Background Zeng et al. (1999) derived skin SST from TAO buoy data using empirical relationship derived from ship obs.:

Zeng and Beljaars (2005) scheme -10  m -1 mm -1 cm -1 m -10 m Depth (m) Nighttime Temperature Daytime Temperature cool skin warm layer TsTs TsTs T-T- T-T- T -d = 0.3 (not a straight line) (based on Donlon et al. 2002) Residual warm layer after sunset:

Zeng and Beljaars (2005) scheme Obs.ZB  ZB compared well to COARE ship observations.  ZB not only for models.

Implementation in CAM3.1  Three runs: CONTROL, TSKIN, RANDOM  TSKIN SST diurnal range > 2 K in TWP, because CAM3.1 produces low wind speeds. (Brunke et al. 2008) (Zeng et al. 1999)

Implementation in CAM3.1  Largest TSKIN – CONTROL over the NW Pacific and over the Bay of Bengal.  RANDOM - CONTROL spatially incoherent over all oceanic regions. (Brunke et al. 2008)

Implementation in CAM3.1  Tropical areas of too low precipitation in CONTROL get more precipitation in TSKIN.  Tropical areas of too much precipitation in CONTROL get less precipitation in TSKIN. (Brunke et al. 2008)

Use in the TWP  ZB mean skin SSTs compare well to MERRA and RAMSSA. MERRA RAMSSA_skin ZB Jan Feb Mar Apr

Use in the TWP  Monthly mean ZB diurnal range is higher than that of RAMSSA. RAMSSA_skin ZB Jan Feb Mar Apr

Use in the TWP  Shrinks the warm layer diurnal cycle temporally.  Worse in comparison to COARE ship observations. Obs.ZB ZB+T For stable conditions in the warm layer: ZB: ZB+T: (Takaya et al. 2010)

Use in the TWP  ZB generally produces higher diurnal cycle on low wind days.  ZB+T comparable to RAMSSA on those days.  Comparison to TMI inconclusive.

Use in the TWP  Diurnal cycle highest by ZB when wind speed low, lower in ZB+T at these times.  Both versions comparable at other times.  Comparison to TMI suggests that ZB, ZB+T, COARE, and RAMSSA diurnal cycle corrections may not be high enough.

Discussion and conclusions  While ZB was originally designed for implementation in models, it is also appropriate for dataset development of skin SST. If you want “sub-skin” temperature, can be easily adapted.  For non-low wind days, ZB skin SSTs agree fairly well with ZB+T.

Discussion and conclusions  Areas of possible improvement: ▫Change in stability function (e.g., ZB+T, Takaya et al. 2010) ▫Effect of waves (e.g., Takaya et al. 2010) ▫Adjustable warm layer depth ▫Interaction with a deeper layer  We don’t have enough observational data locally to test a change to the algorithm at this point.

Implementation in CAM3.1  Increased air temp. and LH flux diurnal cycle in TSKIN. (Brunke et al. 2008)

Implementation in CAM3.1  TSKIN’s cross-equatorial winds higher. More wind crossing subcontinent.  Improved LH fluxes ⇒ wind enhancement ⇒ improved precip. (Brunke et al. 2008)