High Frequency Area Research Articles

A synoptic climatology of satellite observed cloud vortices over the Southern Hemisphere

AbstractA classification scheme for satellite observed cloud vortices is used to assess some general features of the behaviour of Southern Hemisphere depressions. From coincident conventional observations the mean variation of surface pressure and upper level geopotential anomaly near the centre of, and in west‐east cross‐section through an extratropical vortex is determined in relation to its age. Data are obtained on the geographical variation of occurrence of vortex type, duration, and frequency of change between development stages. The percentage of vortices developing without a pre‐existing cloud band is found to be greater at higher latitudes but, in general, over 50 per cent of developments occur in this way.Persistent maxima of early vortex development are found in the western South Atlantic and in the central South Pacific, both regions extending into lower latitudes than elsewhere in the hemisphere. Two less prominent maxima are located in the central Indian Ocean, and south of Australia. Generalized vortex track and speed data are obtained, and several areas of high frequency of termination of depression track are observed at high latitudes near the Antarctic coast.In total, the observations tend to point to a circulation pattern having a high frequency of major long wave troughs east of the Andes, and in the central Pacific, with a further frequent trough more variable in space and time being located between the central Indian Ocean and the longitude of the Great Australian Bight.

Annoyance reactions from aircraft noise exposure

The report presents an investigation on annoyance due to aircraft noise exposure. Social surveys were conducted in 24 areas with well-defined noise exposure characteristics around 8 airports in Scandinavia. About 2900 interviews were performed. The results demonstrate that the extent of annoyance reactions in an exposed population is closely correlated to the noise level of single overflights. For areas exposed to a low number of take-offs the extent of “very annoyed” in the population is below 5% provided the noise levels do not exceed 90 dB(A). For areas exposed to a high number of take-offs an increase in the extent of “very annoyed” is found already when the noise level increases from 70 to 75 dB(A). The increase with noise levels up to 95 dB(A) is linear (correlation coefficient 0·99). The take-off overflight frequency or any other measure of the number of aircraft movements is of importance only for the classification into high and low take-off frequency areas. The threshold value for this differentiation was found to be between 36 and 63 take-off exposures/24 hours. After the classification into high or low take-off exposure areas the noise contours for the noisiest type of aircraft which is common on the airfield will provide the adequate criteria for the hygienic noise limit in each area around an airport. No correction needs to be made for the distribution of take-offs per 24 hours if the traffic pattern is comparable to that valid for the areas investigated here.

Influence of the nose on the acoustic pattern of nasal sounds.

After changing the conditions in the nose on one or both sides, an attempt was made to ascertain the influence of these changes on the formation of the nasals m, n and ng, both by auditory perception and by spectrographic methods1). Complete closure of one side did not cause any change in the auditory perception of the nasals. However, the decrease in, or disappearance of, energy in the higher—frequency areas can be established in the sonagram. Complete closure on one side and partial closure on the opposite side cause changes as follows: As long as the lowest nasal cavity is free, the epipharyngealis—nasal cavity form—ant, which is apparently formed primarily in this area, remains unchanged, i. e. at 250 cps. This is the most important frequency area of the nasals. If the lowest—and only—nasal cavity is closed, the higher frequencies will be intensified, and auditory perception receives plosive characteristics; if complete closure is brought about, the nasals get a corresponding plosive structure. Indivi...

Determination of frequency characteristics of the pressure-detecting system

Evaluation of the pressure-detecting system should be given in terms of both static and dynamic accuracy. Stablility, lineality, sensitivity, and error of the system were discussed in relation to static accuracy. Frequency characteristics is most important in dynamic accuracy. Because of technical difficulty in determining frequency characteristics by steady-state movements in the high frequency area, a substitute method was developed theoretically. Modification of the method applied to the calculation of frequency response and phase lag of the system in damped oscillation was adequate to calculate frequency characteristics. The method applicable both in critically damped and slightly over-damped system was also mentioned.

Some Aspects of High Latitude Southern Hemisphere Summer Circulation as Viewed by ESSA 3

Abstract The computer-generated digital mosaics of daily cloud photographs obtained by the ESSA 3 satellite were studied for the Southern Hemisphere south of 40S for the period of the southern summer, December 1966 to February 1967. The distribution and movement of the large-scale vortex patterns enabled a number of regions of high frequency of cyclones, cyclogenesis and cyclolysis to be located over the ocean areas surrounding Antarctica and the principal trajectories of cyclones over the southern oceans to be examined. These results are in substantial agreement with earlier synoptic studies. Little evidence was found for frequent cyclogenesis at latitudes close to the Antarctic coast and mid-latitude cyclogenesis was frequently observed without classical frontal wave cloud sequences. The areas of high cyclonic frequency and of cycloysis close to the Antarctic coast for the period of the study are found to be consistent with some known features of mean annual precipitation over the continent. Particular ...

The Distribution of Heavy Rainfall Frequency in Western Half of Japan in Baiu Season

Fig. l and Fig. 2 show the distribution of heavy rainfall frequency in June and July respectively. In June (Fig. 1), high frequency areas are in the Pacific side of the district. In July (Fig. 2), the frequency decreases very much in the Pacific side, but it increases in the Japan Sea side. In this reprot, heavy rainfalls are defined as rainfalls that amounted over 50 mm per day.

Distribution of Heavy Rainfall Frequency and its Seasonal Patterns in Tohoku District

In Japan, frequent heavy rainfalls appear bringing floods somewhere every year. In this paper, the author considered the geographical distribution of the frequency of heavy rainfalls in Tohoku District. Drawing the distribution map of the frequency of precipitation above 40mm/day, 60mm/day, 80mm/day and 100mm/day in each month (1922-1941), the author obtained the following results.1) The distribution of high frequency areas of heavy rainfalls is fairly specified in each month, and the more the daily amount of precipitation, the clearer is that tendency. 2) High frequency areas do not always coincide with, the so called rainy areas, for exmaple, heavy snow falls appear often on the eastern slope of the Kitakami Mountains where there is little snow usually. 3) The distribution patterns of the frequency of heavy rainfalls change seasonally. Grouping the patterns, a year is divided into four periods: (a) Feb. -Jun., (b) Jul. -Aug., (c) Sept. - Nov. and (d) Dec. - Jan. 4) High frequency areas are on Pacific side at (a) period (eg., Fig. 1, 2), on the Japan Sea side at (b) period (eg., Fig. 3), on Pacific side at (c) period (eg., Fig. 4), on the backbone range at (d) period (eg., Fig. 5). 5) The four periods do not always correspond to the four seasons of the year, but the seasonal change of the patterns is to be understood in a sense of dynamic climatology. In other words, the pattern of the frequency distribution changes from (a) period to (b) period when the Baiu front passes over Tohoku District, the pattern of (c) period prevails in the season of Typhoon, the pattern of (d) period prevails at the northwestern monsoon time, and that pattern disappears when the monsoon becomes weak at the end of January.

Geographic Variation in the Prevalence of Histoplasmin Sensitivity

Since the demonstration in 1945 of an association between pulmonary calcification and histoplasmin sensitivity by Palmer1 and Christie and Peterson,2 numerous clinical, laboratory, and epidemiological investigations have increased the existing knowledge of histoplasmosis. It is now accepted that histoplasmosis, hitherto known only as a rare and fatal disease, also occurs in a benign and relatively common form; that the infective episode itself usually passes unrecognized; and that a positive skin reaction to histoplasmin, and, less frequently, pulmonary calcification are usually the only testimony of a previous infectious experience. While histoplasmin cross-reacts with coccidioidin and blastomycin, the relative rarity of coccidioidomycosis and blastomycosis leaves the bulk of the positive reactions to histoplasmin specific for infections with H. capsulatum. With these facts established the skin test has become an important epidemiological tool in the study of histoplasmosis. Geography has played a prominent role in epidemiological investigations of histoplasmosis since comparisons of different locations by Palmer3 first showed wide variations in the prevalence of positive reactors. That where one lives influences the probability of being infected with H. capsulatum more than how one lives or with whom is the logical conclusion stemming from statistical evidence based on skin-testing studies carried out in the years since 1945. The slightly higher rates among males,4 among siblings of a positive reactor,5 among rural populations,6 and among whites,4 are all relatively small compared with the variations among groups tested from different geographic areas. There are now available in the literature reports of a number of studies that illustrate the general characteristics of the geographic variation in histoplasmin sensitivity in the United States. It is generally known that people who have spent most of their lives in the mid-central States are much more frequently sensitive to histoplasmin than persons living in other parts of the country; that the highest frequency of reactors occurs in the central Mississippi River Valley; that prevalence tends to decrease with distance from the area of highest frequency; but that wide variations sometimes occur within relatively short distances. Wide differences in the prevalence of histoplasmin sensitivity within the state of Tennessee have been reported by Christie and Peterson.7 Furcolow and Sitterley8 showed that in Kansas prevalence drops sharply as one moves westward from the endemic area in the eastern part of the State. Prior and Allen6 showed similar variations in Ohio, with the highest prevalence in the southwestern

World Distribution of Leishmaniases

This map furnishes comprehensive information on a variety of subjects related to the geographical distribution of visceral, cutaneous and muco-cutaneous leishmaniasis. Centered above on its face is a Briesemeister elliptical projection of the world, showing (in red) different population densities, while the prevailing winds in areas of high frequency of these diseases are indicated by green arrows. Below there is an enlargement of the countries in which the infections are indigenous, with two degrees of density for each (in black for visceral, in red for cutaneous, and in green for muco-cutaneous leishmaniasis). Greater enlargements are found for the Middle and Near East, the countries bordering on the western Mediterranean, and Peru. Additional data include “spotting” with the letter “R” of regions where reservoir hosts have been reported, and names of the species of Phlebotomus proved or believed to be the vectors are recorded near the sites where they have been collected.