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By H. G. BOOKER Ever, Has a Fairly Technical Significance. a Magnetic VOL. 40, 1954 GEOPHYSICS: H. G. BOOKER 931 difficult, provide intensive sets of "direct" data for a short period of time, and this information can be used to "calibrate" indirect data. This, in effect, permits the conversion of large bodies of indirect data into direct data. At the same time, new discoveries are possible by rocket techniques. Some of the types of result attained by rocket explorations are the following: (1) Solar radiation of the shorter wave-lengths, which are absorbed in the upper atmos- phere and hence never reach the earth, has been successfully studied-for example, a rocket measurement led to the discovery of X-rays in one of the ionospheric layers. (2) Solar ultraviolet light measurements from rockets have established the variation of the ozone with height up to an altitude of 42 miles. (3) Electric charge densities in the ionosphere and collision frequencies of the air particles have been measured directly. (4) What are believed to be auroral particles have been detected in rocket- borne Geiger counters. The program calls for the launching of 37 rockoons and 36 Aerobees from sites in New Mexico, Greenland, Canada, and Alaska. (United States firings will be co- ordinated with those of other nations, particularly at those crucial times of unusual solar activity.) Each rocket will carry instrumentation, within the very severe weight limitations, to measure several quantities: atmospheric pressure, tempera- ture, and density; the earth's magnetic field, especially during auroral displays; night and day airglow; solar and ultraviolet light and X-rays; auroral particles; ozone distribution; ionospheric charge densities; and cosmic radiation. The re- sults of these investigations will be integrated with the results of simultaneous measurements made in each of the major fields of geophysics that represent aspects of, or directly involve, the atmosphere. Acknowledgment.-Acknowledgments and thanks are due all the members of the Program Coordination Group of the United States National Committee for the International Geophysical Year and to the many scientists who have given so generously of their time during the difficult period of program preparation. * Chairman, United States National Committee for the International Geophysical Year. MORPHOLOGY OF IONOSPHERIC STORMS By H. G. BOOKER CORNELL UNIVERSITY, ITHACA, NEW YORK An ionospheric storm is a disturbance of the ionosphere that can be easily ob- served by means of an ordinary ionospheric radio recorder, that is to say, radar- type equipment by means of which pulses of radio energy are reflected from the ionosphere at roughly vertical incidence over a frequency range from, say, one to twenty megacycles per second. In thinking of an ionospheric storm, one's mind naturally turns also to a mag- netic storm, there being a close connection between the two. A magnetic storm is a disturbance of the earth's magnetic field, lasting some days and observed by conventional equipment for measuring magnetic fields. A magnetic storm, how- ever, has a fairly technical significance. A magnetic storm is a phenomenon which Downloaded by guest on September 30, 2021 932 GEOPHYSICS: H. G. BOOKER PROC. N. A. S. can be observed all over the world at;the same time and has a sudden commence- ment, the same at all stations within- a few minutes. There are other magnetic disturbances, particularly in the auroral zone, which do not fit into this picture. The term "magnetic storm" is restricted in this paper to the world-wide, sudden- commencement phenomenon. With the ionospheric storm there is some confusion in terminology. There is a phenomenon which occurs at the same time as a magnetic storm, is world-wide in character, and becomes observable at each ionospheric station within an hour or two after the sudden commence- ment of the magnetic storm. Y7 . , . There are, however, other dis- turbances somewhat similar in character, especially near the 10 0 auroral zone. This paper deals 0o with the world-wide features of -Iv 1 -0 an ionospheric storm, which, al- - 0 though not having a sudden commencement, nevertheless seem to start shortly after the lo.. X tO sudden commencement of the O- 0 magnetic storm. The more -lo x0to \ 8 h . complicated phenomena that occur in the auroral zone will 10. V 2 t not be discussed. ID 3> 10 0 There is a further confusion 0 0 _to in terminology to which refer- 10t10 V . ence should be made. An im- to 3Li 10- portant part of the disturbance lo,to 46b floX0 V 0 of the earth's magnetic field 0 .0 during a magnetic storm is iono- . to .o-10 spheric in origin; it arises from I 0 5 0 currents in the ionosphere. 4~_O 0 it is a little odd to 0 Therefore, 0-00 VF:~lo-V:405 to - speak of an "ionospheric storm" -IC* H.F 0 ., 0 on the one hand and a"magneticis kh h K.2 _40oi Lh i. k, D qh !ma 2 4F q oip a4 storm" on the other. It is very FIG. 1.-Daily variations in horizontal field (HF) likely that they are simply and vertical fields (VF) on the' first day of a magnetic different manifestations of the 1ostorm (Chapman). same basic phenomeuoio. Never- theless, there. is a fairly clear- cut distinction between the two. In so far as a magnetic storm arises from currents in the ionosphere, these currents almost certainly flow in the lowei regions of the- ionosphere, whereas the phenomena observed with ionospheric radio recorders and generally referred to as an "ionospheric storm" are primarily phenomena con- nected with the highest layer in the atmosphere, the F-2 region. As observed by an ionospheric 'radio recorder, an ionospheric storm shows very marked effect in the F-2 'region but comparatively small effects in the lower regions of the iono- sphere. Downloaded by guest on September 30, 2021 VOL. 40, 1954 GEOPHYSICS: H. G. BOOKER 933 Let us now turn to some observational data. Figures 1 and 2 show a couple of well-known diagrams from Dr. Chapman's book to illustrate a magnetic storm. Of course the earth's magnetic field shows significant variation even on a quiet day. On a day of magnetic storm it shows an additional diurnal variation, illus- trated by Figure 1. There are statistical methods for separating out (a) the quiet- day variations, (b) additional diurnal variation that occurs during a magnetic storm as shown in Figure 1, and (c) what is called the "storm-time variation," shown in Figure 2. Even after statistical methods have been used to eliminate the quiet-day variation and the diurnal variation shown in Figure 1, there is still a marked variation, particularly in the horizontal component of the earth's magnetic field, extending over several days. This is the storm-time variation illustrated in Figure 2. Batavia.Porto Rico.Honolulu Zikawe, San Fernando. PolaGreenvkhPotdam Cheltenham. Baldwin Pavlovsk. H.F .F .F -'0 -I V.F V.F v.F. 5 5 m % 0 0 Ne, ZZ:7 ~ ~ ~ ~ ~ ~ -5-5 Mee. W.Dec WDec. 5 5 _~~~~~~~~~~~~~~~~~~~~~~~~fe'VP-_s9 -NO 1 Storm time Storm time Stormtme e =tI6v 24' 32" 4 4?, h 6h .h 32P4d h 2hI FIG. 2.-Average storm-time magnetic-disturbance changes in different latitudes (Chapman). Now let us turn to some observations made some years ago by Berknerl and his associates at the Carnegie Institution of Washington, showing what is meant by an ionospheric storm. Figure 3 shows records made by an ionospheric recorder at Watheroo, Western Australia; each little diagram shows virtual height of reflection, plotted vertically, against frequency, plotted horizontally. The maximum fre- quency at which reflection can be obtained from the ionosphere is a measure of the maximum electron density in the ionosphere. The duplication that is seen Yer- tically in the records is due to multiple reflections; that which is seen horizontally is due to the earth's magnetic field. The maximum frequency at which echoes are obtained is proportional to the square root of the maximum electron density in the F-2 region of the ionosphere. The records along the odd rows were taken at hourly intervals and were made two days before a big magnetic storm in March, 1940. These records describe what was happening on a more or less quiet day. Records in the even rows show what was happening after the commencement of the magnetic storm. The records Downloaded by guest on September 30, 2021 934 GEOPHYSICS: H. G. BOOKER PiRoc. N. A. S. are aligned in such a way that, by comparing odd and even rows, one sees the effect of the ionospheric storm. The most obvious feature of the storm is that the maximum electron density in the F-2 region of the ionosphere is substantially reduced, as compared with what it would be on a relatively quiet day. It will also be noticed that the height of re- flection from the F-2 region is substantially increased. It is possible that there is no marked change in the total electron content of the region; if the region were merely expanded during a storm so that it extended over a greater interval of height and had a smaller maximum electron density, effects substantially like those illus- trated in Figure 3 would ensue. * -AfRCW fO ., .1 OA-elssMy a A s .......... FIG. 3A.-Records comparing-ionospheric disturbances at Watheroo Magnetic Observatory during' magnetic storm of March 24-25, 1940, with quiet day conditions of March 22-23, 1940 (Berkner and. Seaton).' .It will also be noticed that records are much more scattered, or spread, during the storm than they are during a quiet period. This is an effect which primarily happens at night.
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