10 



heat transfer and evaporation. Input data included 1000 and 500 mb geo- 

 potential heights, integrated specific humidity (precipitable water), and 

 ocean surface temperatures (time invariant). Output consisted of 1000 and 

 500 mb geopotential, precipitable water, cumulative precipitation, and 

 vertically - averaged vertical motion. The forecasts shown are for 12 hours 

 (computed in one-hour time steps). 



The figures (Spar, et al., I96I) show the initial state, 12-hour 

 forecasts, and verification maps for a case of rapid Worth American east- 

 coastal cyclogenesis beginning at 0300 GMT 10 February 19^7? and permit us 

 to compare forecasts made with and without surface heat and vapor transfer. 



The initial conditions for the forecast experiment are displayed in 

 the three maps of Figure 1 which show the 5OO mb geopotential and temperature, 

 1000 mb geopotential and 1000- 500 mb geopotential thickness, and the 

 vertically-averaged specific humidity. 



Figure 2 illustrates the twelve-hour 500 mb forecasts computed (a) 

 with a barotropic model, (b) with a baroclinic model including heat of 

 condensation but no heat or vapor flux from the sea ("No Flux"), and (c) 

 with a baroclinic model including sea-air fluxes as well as latent heat 

 ("complete"). The verification contours* are shown as dashed curves in 

 Figure 2(A) . It is noteworthy that the baroclinic model predicted the marked 

 deepending that was missed by the barotropic forecast, but that the inclusion 

 of the sea-air fluxes had no significant influence on the twelve hour 

 forecasts . 



The forecast 1000 mb maps, together with the predicted 1000-500 mb 

 thickness patterns are shown in Figure 3 for the "No Flux" (A) and "complete" 

 (b) models. Also shown is the verification map (c) for the 1000 mb level 

 (solid curves) and the thickness (dashed curves). Again the forecasts made 

 with and without sea-air fluxes do not differ significantly in this short 

 time interval. 



The conclusions drawn from these cnide experiments were: 



1. During cyclogenesis the diabatic effects (and this includes also 

 the latent heat release) were second order effects compared with baroclinic 

 effects. This conclusion, i.e., that potential to kinetic energy conversion 

 is the dominant energy transformation in cyclogenesis, is in agreement with 

 the results of many other investigators . 



2. In 12 hours the dynamical effects of sea-air heat and vapor 

 transfer were of little significance . It might be expected that over a 

 longer period the air-sea effects might be more important. But it is 

 noteworthy that the 12-hour period selected \ra,s the one when the cold out- 

 break over the water was strongest, and the heat transfer at its peak. 



