The 4-second summertime micropulsation band at College

Abstract

A significant summertime micropulsation band at •4-sec period is revealed in the several years of continuous micropulsation recording at College. The band contains mainly Pc-type activity, but is also seen in certain weak Pi I bursts. The intensity of the band is greatest in afternoon at College and has a positive correlation with Kv in afternoon. A small diurnal variation in band midperiod was observed, with periods near 4 sec in day and near 3 sec at night. The 4-see events are usually less well structured than higher frequency pearl-type events, and the frequency-time elements are often irregularly spaced. The possibility exists that the 4-see band is due to the principal exospheric resonance. 2763 2764 R. R. HEACOCK rent pearl-type data have been compared to amplitude nighttime bands of micropulsation middle-and low-latitude induction loop data activity at low-latitude sites. The lowest of the by Tepley et al. [1965] with no evidence of bands was frequently in the neighborhood of spurious effects unique to the telluric current 0.25 cps in the evening and midnight hours, system. The telluric current instrumentation tending to rise in frequency in morning hours, has a sufficiently flat response at frequencies and dropping again just before sunrise. The over 0.02 cps for sonagram purposes. The re-bands were sometimes in evidence throughout sponse of the preamplifier, a Tektronix 156a, an entire night. falls off rapidly below 0.02 cps, but this has Benioff's [1960] type B, periods 3-8 sec, oblittle relevance in the present study and in-served in southern California at night during volyes only the lowest several per cent of the times of high K index, may be of the same gensonagram displays that are included in the eral type as the July 1963 examples of Tepley figures contained herein. e• al. [1964]. Since Bentoff recorded continuously for many years, the nighttime occur-I{EVIEW OF PUBLISHED REPORTS OF rence maximum for his type B is assumed to •4-SEC ACTIVITY be accurate for that location. A recent cornpart-The literature on the 4-sec band is rather son of College and Palo Alto sonagrams [Tepmeager. Indeed, it would not be clear, from ley et al., 1965] showed that daytime shortthe literature, that the band exists as a sig-period (T < $ sec) micropulsations are comnificant entity. As will be seen, however, cer-mon at College but are seldom observed at rain consistencies exist in the different reports, Palo Alto. Judging from those studies, together and, when taken together with the College data with the results reported in this paper, it seems reported here, a more unified picture of the 4-likely that Benioff observed only the nightsec band is possible. time portion of a type of activity that is ob-Yanagihara [1963] observed continuous (type served in both day and night at. a6roral-zone Pc) micropulsations in the period range 3-10 sites.

A Theory of Geomagnetic Micropulsations II

“…Heacock (1966) has found a band of micropulsations at T-4 seconds, which is in remarkable agreement with our estimate of exactly the same period in paper I and section 3 above. Lastly, Fernando and Kannanga a (1966) have found pulsations of time period 38+5 and 60*5 seconds which can be compared with our estimates of T-39 and 71 seconds, respectively, in paper I and section 3 above.…”

Propagation of Extra Low Frequency Waves in the Magnetosphere

“…One can compare our results with experimental observations in the following manner. Our estimate of resonances of low amplitude between 7 and 12 s and extremely small ones at 1-5 and 4 s are not probably inconsistent with the observation of Yanagihara (1963) and Heacock (1966): the small resonances between 15 and 36s moderate ones at 37, 39 and 77 and large ones at 30 and 70 s are consistent with the findings of Maple (1959). Our small resonances between 7 and 36, and those at 39,70, 77, 99 and 136s are in the range of observations of Benioff (1960).…”

Geomagnetic pulsations

“…11. night as shown in Figures 11 and 12. The CE amplitude at College shows a very broad maximum in the afternoon-evening period and a minimum in mid-morning (Heacock, 1966). Diurnal variation in the CE period is evident in the lower spectrum.…”

“…The 3.5-sec band of Pcl pulsation (Kato and Saito, 1964b) and the 300 mHz band continuous pulsations , both observed in Japan, and the 4-sec summertime micropulsation observed at College (Heacock, 1966) may belong to the same family because of a similarity in period band and a close resemblance of their characteristics. Although the nighttime bands of the continuous sub-ELF emission observed at middle and low latitudes (Tepley and Amundsen, 1965;Hira-sawa, 1969) have not, according to Heacock (1966), been detected at College, at least a part of these continuous sub-ELF emissions seems to belong to the abovestated family, Pulsations belonging to this family will be reviewed in this sub-section under a tentative name of continuous emission, or CE.…”