R. A. Brown 2003 U. Concepci Ó n

Nov 9 ‘96 18Z Gulf of Alaska rab

Towards a Surface Pressure Model Function A Scatterometer doesn’t measure Winds. It measures Capillaries & Short Gravity waves, related to roughness parameter z o, or u*. This is Easily Extrapolated to: * Fortunately, there exists a relation  P( z o,.…) for the PBL. - Established in UW PBL Models - Verified in 10 years of scatterometer & SAR data/GCM comparisons Fortunately, there exists a relation U(z o,…) for the surface layer. Established over Land, Assumed over ocean. Verified in 23 years since Seasat. R. A. Brown 2003 U. Concepci Ó n

Toward a Surface Pressure Model Function A Scatterometer doesn’t measure Winds. It measures Capillaries & Short Gravity waves, related to z o., u* Fortunately, there exists a relation U 10 /u* = F (z, z o, stratification…). –Established over Land, Assumed over Ocean. –Verified in 19 years since Seasat. There’s an Easy Extrapolation to: Fortunately, there exists a relation U G /u* = F (z, z o, stratification,, ……). –Established in UW PBL_LIB –Verified in 20 years scatterometer data R. A. Brown 2003 U. Concepci Ó n

Evolution of a Pressure Model Function Observation: Surface stress related to surface wind Surface roughness correlates to Surface (Log-layer) wind Surface wind correlates to Gradient Wind &  P Observations: PBL Model = Surface+Ekman Layer with OLE Works well Observation: Satellite  P correlate with NWP Pressures Backscatter correlates with  P RAB 2/97, 11/99 R. A. Brown 2003 U. Concepci Ó n

Why must we consider a PBL (planetary boundary layer) model? The satellite measures the mean density of the capillaries and short gravity waves on the ocean surface. There is no good theory relating this to anything geophysically worthwhile. There exists a raw empirical parameterization between surface roughness and near surface winds (for over flat, smooth land surface). There is a nonlinear analytic solution of the PBL in a rotating frame of reference (but it contains OLE). R.A. Brown PORSEC 2000 R. A. Brown 2003 U. Concepci Ó n

Ocean surface Surface Layer Surface Stress, u* Geostrophic Flow U 10 Ekman Layer with OLE Thermal Wind Nonlinear OLE Non steady-state Advection,centrifugal terms U 10 (u*) effects Stratification Variable Surface Roughness V G (u*) effects  R. A. Brown 2003 U. Concepci Ó n

Let’s try a direct correlation with pressure Since V G =  P / (  f ) Calculate from ECMWF surface pressures; get  P and V G ; substitute V G for U 10 in the Model Function V G correlates with  o as well as U 10 * Better alias selection * High winds appear * Low winds, directions appear * Stratification, Thermal Wind Effects Results: Prospects: R. A. Brown 2003 U. Concepci Ó n

Example of  o vs look angle for U 10 = 20m/s; Incidence = 45  Example of  o vs look angle for V G = 27m/s; Incidence = 45  R. A. Brown 2003 U. Concepci Ó n

Results from Satellite Scatterometer surface pressure analyses :  Agreement with ECMWF pressure fields indicate that both Scat winds and the PBL model are accurate within  2 m/s.  3-month, zonally averaged offset angle (V G, U 10 ) of 19° suggests the mean PBL state is near neutral.  Swath deviation angles show thermal wind, stratification effects.  Higher winds (than GCM or buoys) from pressure gradients agree with OLE effect predictions.  V G rather than U 10 could be used to initialize GCMs R. A. Brown 2003 U. Concepci Ó n

 oV vs look angle, 0 < V G < 50m/s; Incidence angle = 45  R.A. Brown PORSEC 2000 R. A. Brown 2003 U. Concepci Ó n

QuikSCAT plus UW PBL model R. A. Brown 2003 U. Concepci Ó n

ECMWF R. A. Brown 2003 U. Concepci Ó n

Ecmwf analysis QuikScat analysis J. Patoux 2002 Surface Pressures R. A. Brown 2003 U. Concepci Ó n

JPL project winds UW project winds R. A. Brown 2003 U. Concepci Ó n

Southern Hemisphere Pressures ECMWF & NSCAT Comparison Surface Pressure Fields of 102 Storms surveyed for 1996: 25% good matches (-3 mb ave. diff.) 70% misplaced average 280 km 5% missed entirely R. A. Brown 2000 R. A. Brown 2003 U. Concepci Ó n

Early Results from Satellite Scatterometer surface pressure analyses:  Agreement with ‘Surface Truth’ pressure fields indicate that both Scat winds and the PBL model are accurate within  2 m/s.  3-month, zonally averaged offset angle (V G, U 10 ) of 19° suggests mean PBL state is near neutral (1996)  Swath deviation angles show thermal wind, stratification effects.  Higher winds (than GCM or buoys) from pressure gradients agree with nonlinear equilibrium with OLE model predictions.  V G rather than U 10 should be used to initialize GCMs R. A. Brown 2003 U. Concepci Ó n

Buoy winds are not good surface truth GCM PBL models still have wrong physics, too-low winds The  oV saturates (due to white U 10 ~ 35 m/s, but the  oH does not saturate at U 10 ~ 65 m/s The winds are higher, the lows lower & more frequent, heat fluxes greater and stress greater than climatology states. Scatterometer derived pressure fields can be used to de- alias winds, and correct (smooth)  o single or small area anomalies (rain or nadir/edge ambiguities). CONCLUSIONS R. A. Brown 2003 U. Concepci Ó n

Results from Satellite Scatterometer surface pressure analyses :  Agreement with ECMWF pressure fields indicate that both Scat winds and the PBL model are accurate within  2 m/s.  3-month, zonally averaged offset angle (V G, U 10 ) of 19° suggests the mean PBL state is near neutral.  Swath deviation angles show thermal wind, stratification effects.  Higher winds (than GCM or buoys) from pressure gradients agree with OLE effect predictions.  V G rather than U 10 could be used to initialize GCMs R. A. Brown 2003 U. Concepci Ó n

Producing smooth wind fields R. A. Brown 2003 U. Concepci Ó n

Raw scatterometer winds Pressure field smoothed Local GCM smoothed - Dirth