148 MALKUS [chap. 4 



are beyond the provisions of the routine weather services. To date, the two 

 opportunities for such studies in the trades were fortuitous by-products of 

 catastrophe. Tlie first was due to World War II, which required weather ships 

 along the aircrcaft route of the Pacific war theater, and the second resulted from 

 the 1954-55 hurricane invasion of the United States' eastern seaboard, which 

 caused the establishment of an observational network ringing the Caribbean Sea. 



By fortunate coincidence, the Pacific weather stations (Hawaii and three up- 

 wind ships) provided a full season's data along 2400 km of an air trajectory in 

 a region where the trade is steady and two-dimensional. Taking advantage of 

 this opportunity, Riehl and his collaborators (Riehl et al., 1951 ; Riehl and 

 Malkus, 1957) were able to examine the energy transactions in a 3-km deep slice 

 of air following the fiow along this portion of the trade current. By working out 

 mass, water-vapor, heat and momentum budgets for each vertical sub-layer 

 (mixed layer, cloud layer, inversion layer) separately, the mechanisms of 

 energy exchange and transfer were identified. The trade-wind cumulus clouds 

 were shown to be the agency building up and deepening the moist layer down- 

 stream by their myriads of cut-off towers (see Fig. 24). Furthermore the basis 

 for later dynamic treatment (Malkus, 1956) was laid when it was shown that 

 the sensible heat accumulation in the moist layer was responsible for the 

 downstream "pressure head" driving the easterly current against friction. 



To obtain Qs and Qe, necessary ingredients in the energetics and pressure 

 gradient, the authors used the transfer formulas (20) and (21). Lack of oceano- 

 graphic data prevented a separate test of these by the energy-budget method, 

 although comparisons between joint atmospheric heat and water requirements 

 were highly satisfactory. Their wind (pilot balloon) data gave out at about 3 km 

 elevation, so that little could be said about the upper layers, except that local 

 precipitation heating was inadequate to balance radiation loss. About 53-63% 

 of the accumulated moisture was laterally exported equatorward, while most 

 of the remainder (27% of that accumulated) was precipitated in the local 

 cloud layer below 3 km. 



a. Joint air-sea energy budget study of the Caribbean region 



The hurricane-inspired ring of fourteen radiosonde-radiowind stations en- 

 circling the Caribbean Sea (Fig. 25) permitted an upward extension and 

 reapplication of the approach of Riehl and collaborators to an important 

 portion of the trades; this opportunity was seized by Colon (1960). Here, 

 fortunately, there were also enough oceanographic data to undertake a joint 

 air-ocean budget. To our knowledge, this is the first time that such a joint 

 study has been carried through to and checked by its mechanistic and dynamic 

 implications. It will be of considerable value to all marine scientists to under- 

 stand the approaches, difficulties and questions raised by such an inquiry, as 

 well as to learn of its physical results in a region which mothers both the Gulf 

 Stream and much of North American (and probably hemispheric) weather 

 patterns. 



