80 



GENERAL METEOROLOGY AND FORECASTING 



data based on one-way communication confirmed the 

 radar investigations. 



Mediterranean Region. The campaign in this region 

 provided good opportunities for the study of local 

 propagation conditions. The seasonal variation is 

 very marked, with superrefraction more or less the 

 rule in summer, while conditions are approximately 

 standard in the winter. An illuminating example is 

 provided by observations from Malta, where the 

 island of Pantelleria was visible 90 per cent of the 

 time during the summer months, although it lies be- 

 yond the normal radar range. 



Superrefraction in the Central Mediterranean area 

 is caused by the flow of warm, dry air from the south 

 (sirocco) which moves across the ocean, thus pro- 

 viding an excellent opportunity for the formation of 

 ducts. In the winter, however, the climate in the 

 Central Mediterranean is more or less a reflection of 

 Atlantic conditions and hence is not favorable for 

 duct formation. 



The Arabian Sea. Observations covering a con- 

 siderable period are available from stations in India, 

 the inlet to the Persian Gulf, and the Gulf of Aden. 

 The dominating meteorological factor in this region 

 is the southwest monsoon which blows from early 

 June to mid-September and covers the whole Arabian 

 Sea with moist equatorial air up to considerable 

 heights. Where this meteorological situation is fully 

 developed, no occurrence of superrefraction is to be 

 expected. In accordance with this expectation, all the 

 stations along the west side of the Deccan report 

 normal conditions during the southwest monsoon 

 season. During the dry season, on the other hand, 

 conditions are very different. Superrefraction then is 

 the rule rather than the exception, and on some oc- 

 casions very long ranges, up to 1,500 miles (Oman, 

 Somaliland), have been observed with fixed echoes 

 on 200-mc radar, based near Bombay. 



When the southwest monsoon sets in early in 

 June, superrefraction disappears on the Indian side 

 of the Arabian Sea. However, along the western 

 coasts conditions favoring superrefraction may still 

 linger. This has been reported from the Gulf of 

 Aden and the Strait of Hormuz, both of which lie 

 on the outskirts of the main region dominated by 

 the monsoon. The Strait of Hormuz is particularly 

 interesting as the monsoon there has to contest 

 against the "shamal" from the north. The Strait 

 itself falls at the boundary between the two wind 

 systems, forming a front, with the dry and warm 

 shamal on top, and the colder, humid monsoon 



underneath. As a consequence, conditions are favor- 

 able for the formation of an extensive radio duct, 

 which is of great importance for radar operation in 

 the Strait. 



The Bay of Bengal. Such reports as are available 

 from this region indicate that the seasonal trend is 

 the same as in the Arabian Sea, with normal condi- 

 tions occurring during the season of the southwest 

 monsoon, while superrefraction is found during the 

 dry season. It appears, however, that superrefraction 

 is much less pronounced than on the northwest side 

 of the peninsula. 



The "Pacific Ocean. This region appears to be the 

 one where, up to the present, least precise knowledge 

 is available. There seems, however, to be definite 

 evidence for the frequent occurrence of superrefrac- 

 tion at some locations, e.g., Guadalcanal, the east 

 coast of Australia, around New Guinea, and on 

 Saipan. Along the Pacific coast of the United States, 

 observations indicate frequent occurrence of super- 

 refraction, but no statement as to its seasonal trend 

 seems to be available. The same holds good for the 

 region near Australia. 



In the tropics there is a very strong and persistent 

 seasonal temperature inversion, the so-called trade 

 wind inversion. It has no doubt a very profound 

 influence on the operation of radar and short wave 

 communication equipment in the Pacific theater. 



9.7 



RADAR FORECASTING 



The forecasting of propagation conditions for early 

 warning radars is of great operational significance be- 

 cause ranges for airplane as well as ship targets often 

 vary by as much as a factor of 2 or more depending 

 on the weather conditions. Forecasting is based on 

 the general meteorological principles presented above 

 which can be organized into a system of standard 

 procedures for the prediction of propagation in a 

 given area. 244,253,255 It is usually quite difficult to 

 make a quantitative forecast of such parameters as 

 duct height, but this has been tried with a fair 

 degree of success. 



A radio forecast is made by first taking the general 

 synoptic weather situation as presented on a weather 

 map and including such upper air data as may be 

 available. Usually one forecast cannot be applied to 

 more than a limited area of specific local conditions ; 

 fortunately such a forecast is in general adequate for 

 the area covered by one or a few radar sets. The 



