Upon reaching the centre or the " eye " the weather observer makes a 

 complete observation. Particular care is taken in computing the height 

 of the 700 millibar level. An effort will be made to determine the slope 

 of the centre if a slope exists. From radar scope readings the weakest 

 quadrant is determined, and the aircraft then departs the centre through 

 that weakest quadrant to the radius of 50 or 60 knot winds, where a 

 spiral descent and sounding is made. The typhoon will then be circum- 

 navigated, using the same procedure as in the case of a storm. To better 

 evaluate the equation evolved by Bjerknes and Holmboe the typhoon 

 should be circumnavigated in the area of typhoon force winds. This 

 will vary, of course, but in all events circumnavigation is made as nearly 

 symmetrical as possible. The best radius to utilize is the one which 

 places the track of circumnavigation between the inner ring of cumulo- 

 nimbus and the outer ring of towering cumulus. The relative intensities 

 of the quadrants is obtained by radar or actual flight and reported to 

 the typhoon centre. 



As in fixed track reconnaissance, coded reports are relayed at all 

 times plus such plain language messages as are required to present the 

 proper weather picture. Data transmitted includes temperature, surface 

 winds, maximum surface winds, cloud types and amounts, relative 

 humidity, present weather, past weather, turbulence and any special 

 phenomena observed, such as icing or lightning. 



A cross-section is made showing cloud type and amount of weather, 

 turbulence, icing level, wind direction, and force with the observation 

 positions labelled giving position in degrees and tenths. 



After return to operating base the observer immediately makes a 

 post-flight summary from information obtained while in flight. Post- 

 flight summaries give a narrative of the weather encountered and a 

 description of the tropical storm or typhoon. Post-flight summaries 

 are given the same dissemination as in-flight typhoon reconnaissance 

 reports, and are extremely valuable to the forecasters who are responsible 

 for typhoon warnings. 



It is a common belief that aerial weather reports are of less value than 

 surface reports. This belief not only exists among laymen but also 

 among large groups of trained meteorologists, and it is frequently difficult 

 to dispel their ideas concerning the value of such reports. However, 

 after a season's work in areas where reconnaissance reports are frequently 

 the only ones available, they become adamant about the need for more and 

 more weather reconnaissance reports. 



Regardless of this, the fact remains that reconnaissance reports are 

 extremely valuable not only for their timeliness, mobility, and frequency, 

 but because such observations are what may be called three dimensional. 

 To the observer on the surface observations above the lower stratus deck 

 are impossible to take. The surface observer cannot observe the various 

 clouds above such a level, and therefore has little conception of the many 

 cloud decks, their configuration, and their direction of movement. The 

 only method of upper air observations during poor weather are rawin or 

 radiosonde, and these are frequently not usable or incomplete due to 

 high winds limiting the time of observation and other atmospheric 

 phenomena, such as static interference hindering the run. 



15 



