Contains research objectives and reports on two research projects.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 36-039-AMC-03200(E)National Aeronautics and Space Administration (Grant NGR-22-009-131)National Aeronautics and Space Administration (Grant NGR-22-009-(114)

Bitter, F.

Fiocco, G.

Grams, G. W.

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X. GEOPHYSICAL RESEARCHA. High Magnetic FieldsAcademic and Research StaffProf. F. BitterProf. G. FioccoGraduate StudentsS. J. BlessRESEARCH OBJECTIVESThe approach to the problem of producing megagauss fields by capacitor dischargehas been changed from the conventional one of using a single-turn coil in which the mag-netic pressure is directed outward, to the use of a Z-pinch in which the magnetic fieldsurrounds a short straight conductor, and the magnetic pressure is directed inward. Thereasons for this change follow.1. The stored capacitor energy is first converted almost entirely into magneticenergy, and not simultaneously into kinetic energy, because of explosion. A very modestinstallation, 20 kJ, can produce fields of several megagauss.2. If the current carrying rod is sufficiently large (a few millimeters in our instal-lation), it is only partly evaporated by a discharge, and the factors influencing perform-ance can be quantitatively studied. In particular, the amount of material melted andevaporated, and the temperatures reached by the current-carrying sheath, called theM-M (metal-megagauss) interface, can be investigated.3. In certain ranges, the pressure produced by the Z-pinch may be useful for solid-state studies.The apparatus is to consist of eight 15-f capacitors operated at 20 kV, connectedthrough spark gaps to the periphery of 2 reinforced metal plates, 3 ft in diameter. Theyare shorted at the center by replaceable rods of variable length and diameter.Preliminary experiments with only 4 or 5 of the capacitors used have produced mod-erately damped discharges with 1/4 period of approximately 1 psec. A field of 1.5 Mgaussis estimated to have been produced around a Mo rod, 1 cm long and 0.4 cm in diameter.It is interesting to note that approximately 15 kJ/cc are required to evaporate copperor steel, whereas discharges of this magnitude have passed through rods having a totalvolume of ~0. 25 cc apparent melting and evaporating over only a thin surface layer,~0. 05 cm. Further study is needed to determine how the capacitor energy is dissipated.It is possible that it goes to heating the M-M interface. Further experiments along thisline are contemplated during the next few months with the completed apparatus.An interesting research program in which the methods described above for producingmegagauss fields could be used would be to test the theoretical predictions in the paper"High Energy Electromagnetic Conversion Processes in Intense Magnetic Fields" byThomas Erber, Rev. Mod. Phys. 38, 626 (1966).F. Bitter, G. FioccoThis work is supported in part by the Joint Services Electronics Programs(U. S. Army, U. S. Navy, and U. S. Air Force) under ContractDA 36-039-AMC-03200(E).QPR No. 84X. GEOPHYSICAL RESEARCHB. Upper Atmospheric PhysicsAcademic and Research StaffProf. G. FioccoDr. G. W. GramsDr. Sharda NandGraduate StudentsJ. B. DeWolfD. F. KitrosserH. C. KoonsRESEARCH OBJECTIVES AND SUMMARY OF RESEARCHMuch of the research in our group is concerned with the properties and use of coher-ent light in connection with problems of atmospheric physics. The NASA trailer hasbeen instrumented as a mobile laboratory for research in atmospheric optics and con-tains the optical radar, as well as other instrumentation.For about a year, we have been analyzing the results of measurements carried outwith the optical radar during 1964 and 1965. These measurements provide profiles ofthe optical backscattering cross section of the atmosphere as a function of altitude andare interpreted to supply information on the dust content of the atmosphere from 10 kmto 150 km. The analysis of a large sample of the stratospheric data has been completedand will be published soon. These observations of the stratospheric aerosols were madeat Lexington, Massachusetts, during the two-year study and also at College, Alaska, inthe summer of 1964.The data have been compared with various meteorological parameters associatedwith conditions in the lower stratosphere. A significant negative correlation betweenfluctuations of dust and ozone has been found in the measurements.At present, we are concerned with the reduction of data in the 35-150 km range.Although difficulties in the reliable operation of a semiautomatic digitizer have sloweddown the data reduction, we hope to complete the reduction early in 1967.We expect to be able to study the mesospheric dust content, its possible relation tothe electron recombination in the D-region, as well as the possible influx of micromete-oric materials and its relation to E-region ionization.With regard to the first problem, we are interested in the possibility of simulta-neously performing dust density measurements by optical radar and electron densitymeasurements by rocket, and are considering collaborative efforts with other groups.The production of ionization by micrometeorites have been investigated for a simplemodel based on the acceleration of upper atmospheric molecules by incoming micromete-orites and the successive neutral-neutral ionizing collisions. It is found that a con-servative value of 4 X 103 tons/day for the influx rate of cosmic dust on Earth issufficient to produce ionization in amounts found in the E-region at night; since thereis still no satisfactory explanation for the formation of the E-region at night, this isprobably a significant result. The results of this will be submitted for publication.*This work is supported principally by the National Aeronautics and Space Adminis-tration (Grants NGR-22-009-131 and NGR-22-009-(114)), and in part by the Joint Ser-vices Electronics Programs (U.S. Army, U.S. Navy, and U. S. Air Force) underContract DA 36-039-AMC-03200(E).QPR No. 84(X. GEOPHYSICAL RESEARCH)Another aspect of the role of dust in the upper atmosphere with which we are con-cerned, at present, is its relation with rainfall; we have correlated fluctuations ofstratospheric dust amounts with the occurrence and amounts of precipitation, but, thusfar, we have been unable to find a relationship. We expect to extend the investigationto include mesospheric dust and thus check the validity of Bowen's hypothesis.Essential to the interpretation of the optical radar data is the availability of theoret-ical backscattering cross sections for spheres and ensembles of spheres with specifiedsize distributions. We have extended existing computations to cover a wide range ofcomplex values for the refractive index and have considered a variety of size distrib-utions. The computations are almost complete, although we are facing the task of ameaningful yet compact presentation of the data.We shall also extend the computations to cover scattering angles different from 1800;these tables will be of use in interpreting photometric and visual observations of scat-tering from the zodiacal light and from atmospheric stratifications, as well as an aidin estimating the feasibility of forward-scattering optical communication links.Some estimate will also be carried out of the effects of various aerosol distributionsover the response of the Dobson photometric technique for the measurement of atmos-pheric ozone.During the summer 1966, the optical radar was taken to Norway to continue the inves-tigation of noctilucent clouds which was initiated in 1964. Several noctilucent displayshave been observed and we have collected a very large amount of data that is now beinganalyzed.An important advantage of the optical radar technique when applied to noctilucentclouds is that, since our observations are performed at night as well as at twilight, weshould be able to describe the development of the cloud when no other techniques ofobservation are available. From the 1964 data we inferred the possibility of substantialvertical motion for the cloud, and hope with present data to be able to substantiate theearlier findings.The stratospheric aerosol layer was also observed continuously in Norway duringthe summer 1966; we intend to draw a comparison with activity in the previous yearsand establish the presence of a latitudinal gradient in the concentration which was sug-gested in the earlier work.An OH airglow meter that utilizes photon counting techniques is being developed andwas also operated in Norway during observation of noctilucent clouds. The importanceof studying OH is based on (a) its role in the dissociation of H 2 0 (H 2 0 is possibly a majorconstituent of noctilucent clouds), (b) the fact that the excitation of the rotational-vibrational bands of OH probably reflects the ambient temperature of the mesophere, and(c) the relation between OH and Na airglow activity. We are designing a multichannelphotometer to scan simultaneously several airglow lines.Another area of interest in our group is the measurement of atmospheric tempera-tures by the broadening of laser radiation backscattered by air molecules. We havetheoretically analyzed and partially implemented schemes for heterodyne and homodynedetection, as well as more conventional schemes utilizing optical filtering, and weare now assembling a system consisting of a high-power Ar+ laser of high spectralpurity, and a pressure-scanned Fabry-Perot interferometer.We are now becoming interested in the generation of high power at the wavelengthof optical transitions of atmospheric gases; the possibility exists that, because ofresonant scattering, cross sections would be greatly enhanced, thereby enablingobservation of the presence of even minor constituents in the upper atmosphere andin the laboratory. We are carrying out experiments to explore the practicalityof carrying out observations at the following wavelengths: 6560. 1 A (He+), 3582 A (N2),QPR No. 84(X. GEOPHYSICAL RESEARCH)6707. 9 (Li), 5973 (O 2), 5889 (Na), 7698. 9 and 7665. 9 (K), as well as other transitions.It would appear that it is possible to generate high outputs at these wavelengths bythe combination of Raman effects, second-harmonic effects, and thermal tuning of laserlight. The possibility of measuring the linewidth of resonant transitions in laboratoryplasmas, by tuning the laser to a specific transition, suggests a method for the measure-ment of the concentration, as well as the temperature, of ionic species.Further work on the laser scattering-diagnostic technique for plasmas, firstdeveloped in this laboratory, is now being carried out. We are making observations ofincoherent scattering of pulsed ruby laser light in a reflex discharge and modifying thesystem to study the possibility of observing scattering from a CW Ar+ laser light; theuse of a relatively low-power, continuous source would be a great advance in the prac-ticality of this diagnostic tool.G. Fiocco1. POSSIBLE RELATION BETWEEN DUST AND RAINFALLSince the nucleating properties of dust provide a mechanism for starting the conden-sation of water vapor, the vagaries of weather might be somewhat related to fluctuationsof the dust content of the atmosphere. Bowen1 , 2 has furnished evidence that peaks inaverage amounts of daily rainfall followed, with approximately one month time lag, thedates of known meteor showers; this suggests that meteor showers influence worldrainfall.These results have been the object of controversy (see, among others, Martyn, 3Kleine and Brier,4 and Rosinski and Pierrard5). One criticism is that, because of thelarge variety of sizes expected in the dust influx and of the resultant difference insettling velocities, it would appear difficult to preserve the necessary coherence in thevertical transport process to determine detectable effects.We have made observations of the dust content of the atmosphere at Lexington,Massachusetts, for almost 2 years, in 1964 and 1965, and data related to the strato-spheric dust content are now available. The data were obtained by observing with anoptical radar the echoes backscattered by atmospheric constituents and comparing theirintensities with the returns that one would obtain from a dust-free atmosphere (seeFiocco and Grams, 6 and Grams and Fiocco7).The optical radar technique is particularly sensitive to particles in the size range~0. 1-1 11 radius, since a transmitted wavelength, X = 0. 094 i, is utilized. This is thetypical spectrum of particle sizes obtained in the stratosphere by balloon and aircraftcollections.The dust content of the stratosphere during the period of study was an order of mag-nitude larger than usual, because of the injection of volcanic material following theeruption of Mt. Agung, in 1963. It is therefore doubtful whether any of the features ofthe stratospheric aerosol layer at the time of observation could be attributed to theQPR No. 84(X. GEOPHYSICAL RESEARCH)influx of extraterrestrial dust.Since our study has provided us with a record of the stratospheric dust content andits fluctuations, we have correlated the relative dust amounts at heights of 12 kmand 16 km with the daily amount of precipitation averaged among 103 stations inNew England,8 in order to establish whether some relationship with rainfall might exist.Although the stratospheric dust smounts are probably not related to meteoric activity,one might expect the incursion of stratospheric dust into the upper troposphere to affectthe amount of rainfall, regardless of the source. The time scale for stratospheric-tropospheric exchange is difficult to specify, however, since such processes are, atbest, only poorly understood. The times involved in the vertical diffusion from the lowerstratosphere to the upper tropopause may be several weeks (Junge et al. 9 ). The lengthof time necessary to introduce stratospheric dust into the troposphere makes it almostnaive to assume that a correlation between the two local parameters might be found. Ourstudy of the stratospheric dust layer (Grams and Fiocco, 7 ) indicated a degree of persist-ence of stratospheric dust amounts involving time periods of almost a week. Assuminga wind velocity of 20 m/sec, one may estimate the length scale of a stratospheric dust"cloud" to be of continental dimensions. This lends considerably more justification forcomparing the rainfall figure for the New England states with the stratospheric dust-1.01.0-1.0-1 .0Z iI~iii 11 -tlttTTT i rrm r 1l: T ; i I II T, I;I ! i'I  ltctf-r-ttt ti......... = # l !-tt LL; t tffLT-i I[ I ]~tt *t? t+ :~~t w tt- I I I : 1i :[, i i[1 il][[ili tt f i~f 1~fiet~t- c~~tt mt I : I1 niIr 1 Ii~ l ~ :l~.- LfLt , -:1Ctt:! ~tKK~'~~ err : 1 i L[ i I Inr I I 1l '[[:l ! I 1 il ! lIl Ilfrtt~trrrr~mLi I I I 1 I-60 -40 -20 0 20 40 6(DAYS AFTER RAINFALL MEASUREMENTFig. X-1. Correlation coefficient for rainfall and stratospheric dustmeasurements as a function of time lag.QPR No. 84 67Jt-i 1I1 Iii iiii lll 1iII -1 'T _7 7 7 F-7 7 iT i*:I: tt--t -i~trrtt(X. GEOPHYSICAL RESEARCH)measurements carried out at Lexington, Massachusetts.The curves in Fig. X-1 show the correlation coefficient as a function of the time lagbetween the measurements of the dust content at different heights and the averagedmeasurements of rainfall. The correlation coefficients have been computed by usingapproximately 60 pairs of data. Although small positive peaks are apparent for timelags of 15-25 days, these might be ascribed to the limited size of our statistical sample.No evident trend exists to indicate a correlation between the two physical quantities.Such correlations are only indirectly a test of Bowen's hypothesis. In order toestablish a meteoric effect on rainfall, we should perhaps try to correlate mesosphericamounts of dust with rainfall. In fact, the mesospheric amounts of dust should be relatedto meteoric influx, and a local measurement of it should exhibit more global featuresthan a local measurement of stratospheric dust. Data related to the mesosphere havealso been collected and will be available for such analyses at a future data.G. Fiocco, G. W. GramsReferences1. E. G. Bowen, "The Influence of Meteoric Dust on Rainfall," Australian J. Phys. 6,490-497 (1953).2. E. G. Bowen, "The Relation between Rainfall and Meteor Showers," J. Meteorol. 13,142-151 (1956).3. D. F. Martyn, "Comments on a paper by E. G. Bowen entitled 'The Influence ofMeteoric Dust on Rainfall'," Australian J. Phys. 7, 358-364 (1954).4. D. B. Kleine and G. W. Brier, "A Note of Freezing Nuclei Anomalies," Mon. Wea.Rev. 86, 329-333 (1958).5. J. Rosinski and J. M. Pierrard, "On Bowen's Hypothesis," J. Atmos. Terrestr.Phys. 24, 1017-1030 (1962).6. G. Fiocco and G. Grams, "Observation of the Aerosol Layer at 20 km by OpticalRadar," J. Atmos. Sci. 21, 323-324 (1964).7. G. Grams and G. Fiocco, "The Stratospheric Aerosol Layer during 1964 and 1965"(submitted to the Journal of Geophysical Research).8. Hourly Precipitation Data, New England, U. S. Department of Commerce, WeatherBureau, Vols. 14 and 15, 1964 and 1965.9. C. E. Junge, C. W. Chagnon, and J. E. Manson, "Stratospheric Aerosols,"J. Meteorol. 18, 81-108 (1961).QPR No. 84

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