"I — I — I — I — I — I — r 



n — I — I — I — I — I — I — I — I — I — r 



1050 

 1025 

 lOOO 

 975 



10 11 12 13 14 15 



JULY 1961 

 FIGURE 13 Surface weather conditions, ARLIS II, 1 — 15 Jul/ 1961 



ice "by atmospheric pressure, is veil adapted for this study. Power spectra 

 for each of the five 90-minute intervals vere computed, corrected for instru- 

 ment response, and plotted in figure l6. A low lag number (20) was used to 

 increase the accuracy of spectral estimates. The most noticeable character- 

 istics of spectra plotted on the same set of coordinates are close dependence 

 of power density on local windspeed at all periods and increase of power 

 density with period. Even with the low resolution used in this example, dis- 

 tinct peaks appear and are probably real; instead of appearing to follow a 

 set pattern, they shift slowly with time as mentioned in section 3(<3-)» 



Very little is known about the properties of these short-period pressxire 

 waves — whether they are in fact progressive waves and, if so, how fast they 

 propagate. Waves similar to these have been observed on land by Flauraud et 

 al. (195^) while studying micropressure waves with periods of 5 to 100 minutes 

 with a tripartite array in the Boston area. Waves of 5- "to 100-minute periods 

 propagated with velocities of 20 to 175 knots and were correlated with winds 

 at the 200-mb level. Wave periods less than 10 minutes were not conservative 

 over the length of the array (6 to 9 miles), thus little was learned about 

 their propagation characteristics. Martyn (1950) showed that micropressure 



27 



