PROCEEDINGS OF T'HE IRE

Problems of the Upper Atmosphere*TALBOT A. CHUBBt

Summary-The Upper Atmosphere' can be examined from manypoints of view. For example, it can be considered as an aerodynamic,chemical, or electrical medium. This paper tabulates key parametersused in describing various atmospheric models and gives a briefindication of the instrumentation used in their measurement.

THE BASIC PROBLEMS of a geophysical scienceare twofold. First is the problem of defining thecondition of the environment or object under

study. What parameters describe the object? What niu-merical values do these parameters assume? What enm-pirical laws relate these parameters? The second prob-lem is that of determining why particular parametershave the numerical values which are observed. In otherwords how does one explain the character of the objectin terms of physical, chemical, or geological principles?The upper atmosphere is one of those geophysical ob-jects which is sufficiently simple that it lends itself toquantitative study. It is also onie of those objects forwhich much basic experimental data is lacking. An ac-curate description of the upper atmosphere and onie'sunderstanding of its underlying processes must rest upoInsuch data. It is the purpose of this paper to list sonie ofthe basic parameters which describe the upper atnmos-phere and in turn to indicate types of instrumentationwhich have been used to study them.

In our consideration of the problems of the upperatmosphere it is helpful to keep in mind that the upperatmosphere has many aspects. In one approximation itcanl be coinsidered as simply a static medium whose keyparameters are the aerodynamic paramieters: denisity,temiiperature and pressure, as functions of altitude, geo-graphic coordinates, and time. In another degree of ap-proximation it is considered as a chemical fluid made upof individual chemical constituents. In this case one isconcerned with molecular partial pressures and relativechemical concentrations as well as the standard aero-dynamic parameters listed above. Another aspect of theupper atmosphere is its electrical aspect. When viewedin this aspect one is concerned with electron densities,ion composition, negative ion concentrations anid thelike. We will try to consider the atmosphere from anumber of these viewpoints and to give tables of some

* Received July 30, 1962.t U. S. Naval Research Laboratory, Washington, D. C.I There is no well established definition of the term "Upper

Atmosphere." For the purposes of this paper we consider as "UpperAtmosphere" that portion of the atmosphere which is studied prin-cipally by means of rocket or satellite borne instrumentation, i.e.the atmosphere above 40 km.

of the more useful parameters pertinent to these variousviews.

First let us consider the atmosphere as a simple staticfluid. In Table I we define a number of the paramletersused to describe our medium. As menitionied previously,each parameter is a function of altitude, geographic co-ordinates, and time. This functional depenidence oni timiieand position is implicit in all the tabulations which wewill present and should be kept in mliind by the readerthroughout the paper.To study the atmospheric fluid we mnake use of the

tools of the vacuumn engineer. We use the vast variety ofvacuum gauges which he has developed; such as theionizationi gauge, the Philips gauge and the Pirani gauge.However, we are forced to use these gauges in a movingrocket and hence we must be coontinually concernedwith problems of gas flow into and out of the m10ovin1ggauge openinig, with problemls of ramii and angle ofattack and eveii with probleiiis of clhaiigiing gauge sensi-tivity due to changes in gas composition as the atmos-phere is sampled at varyinig altitudes. We m11ust also beconcerned with vacuuIm1 leaks froml the iniside of therocket to the outside. In the upper atmlosphere pressturesare so low that even a smnall leak caii create a cloud ofrocket gas contamination around the imeasuring instru-menit anid invalidate results. However, offsettinig thesedifficulties is the possibility of uising other techniiqLuesnot readily useful in the smiall vacuumii tank, such as:microphonie density gauges, which make use of satellitevelocities for raiin; and suniset sodium releases fromn aprobing rocket, which permit direct mneasuremient ofhigh altitude temiiperatures fronm the grounid by lookinigat the Doppler profile of the resonantly scattered yellowsodium light. Another technique inot utilized oni theground is the X-ray absorptioni method where the depthto which X-rays fromn the suni penietrate the earth'satmosphere serves to imieasure the overhead air miass inthe 100-200 kmii regioni.The cheimiical fluid model of the atmnosphere has as its

chief anialytic tool the imiass spectromleter. The massspectrometer acts as a set of density gauges, onie for eachof the constituents of the atmiiosphere. Hence, it suffersfromii some of the problems inherent in the use of vacuumgauges. Onie of the m11ost serious of these probleimis is theproblemn of recombiniation of chemically reactive speciesin the entranice port of the device. Somiietimies such re-actionis cani in principle be miade use of; e.g., it has beenisuggested that the reaction 0+ C13--CO29 might be usedfor studyinig the partial denisity of atomnic oxygenL by

2198 'Vovember

Chubb: Problems of the Upper Atmosphere

TABLE IPARAMETERS FOR STATIC FLUID MODEL OF ATMOSPHERE

General Neutral Atmospheric DescriptionParameters

1) Density Mass of air per unit volume. gm cm-3

2) Pressure Force per uinit area exerted by gas on surface boundaries. dyne cm-2

3) Temperature Measure of average kinetic energy of molecules. degrees Kelvin

4) Density scale height Change in vertical distance required to change density by factor I/e. cm

5) Pressure scale height Change in vertical distance required to change pressure by factor Ile. cm

6) Overhead air mass Integrated mass of air above given altitude. gm cm-2

7) MolecuLlar number density Total number of molecules per unit volume. cm'3

8) Mean molecular mass Average molecular weight of constituent molecules. pure number

TABLE IIPARAMETERS FOR CHEMICAI FLUID ATMOSPHERE-MOLECULAR OXYGEN

Composition Parameters (02) Description Units

IA) Partial density of 02 That part of density contributed by 02. gm cm-3

2A) 02 partial pressure That part of pressure contributed by 02. dyne cm-2

4A) 02 density scale height Change in vertical distance required to change partial density of 02 by factor Ile. cm

5A) 02 partial pressure scale height Change in vertical distance required to change 02 partial pressure by Ile. cm

6A) Overhead 02 air mass Integrated air mass of 02 above given altitude. gm cm-2

7A) 02 number density Number of 02 molecules per unit volume. cm-3

9A) Relative 02 number concentration 02 number density divided by molecular number density. pure number

10A) Relative 02 mass concentration 02 mass density divided by total density. pure number

employing a mass spectrometer and studying the mass29 peak. The C13 used to tag the atomic oxygen wouldconsist of a coating on the entrance port. Table II listsparameters used to describe the molecular oxygen upperatmosphere. A more complete description of the chemi-cal fluid atmosphere would include sets of such tablesfor 0, N, N2, A, NO, OH, CO, H, He, dust grains ofvarious sizes, Na, metallic meteoric ions, and atoms andmolecules in various excited states. Ion densities couldalso be included here; we are saving them, however, forthe "electrical fluid" model described below. Anotherchemical or thermodynamic parameter which might alsobe included in Table II is the chemical energy per unitvolume contained in the various atoms, free radicals,and metastable molecules making up the fluid.

For the radio engineer and ionospheric physicist, themost interesting model of the atmosphere is the "elec-trical fluid" model. Here one is concerned with electrondensity and electron collision frequency, parameterswhich determine the reflection, refraction and absorptionproperties of the ionosphere for radio waves. One isinterested also in positive and negative ion concentra-

tions and in production and recombination rates in-volving the various species present. Thus once again weare concerned with sets of parameters equivalent tothose tabulated for molecular oxygen in Table II. Forthe "electrical fluid" atmosphere we are concernedmainly with the electron, 0+, NO+, 02+, N2+, N+, metallicions, 02- and NO2-. We are concerned too with the addi-tional set of parameters listed in Table III. Our tools forstudy include electron density gauges, methods involvingmeasurement of radio wave index of refraction as afunction of frequency, powerful ground based radartransmitters combined with sensitive receivers designedto look for incoherent scatter, ionospheric sweep-frequency sounders, ionospheric cosmic noise signalstrength meters (riometers) and ion mass spectrometers.

All the atmospheric model types discussed thus farare what might be called quasi-static models; i.e., al-though they involve parameter changes with time andposition, they do not include the dynamic effects of fluidmotion or of charge transport. The upper atmosphere asit actually exists is a region of strong winds and windshears and a region of current sheets. There are also

1962 2199

PROCEEDINGS OF THE IRE

TABLE IIIPARAMETERS FOR ELECTRICAL FLUID ATMOSPHERE OF TYPE NOT SHOWN IN TABLE II

Electrical Fluid Parameters

3B) Electron temperature

3B1) Ion temperature

11B) Electron mean free path

12B) Electron collision frequency

13B) Total electron recombination co-efficienit a

14B) Electron production rate

151B) Magnetic field vector

166B) Critical frequency

Description

Measure of average electron kinetic eniergy.

Measure of average ion kinetic energy.

Average distance electron travels between collisions.

Average nuLmber of electron collisions per second.

If R=number electronis recom1bininig each second in 1 cc then a defined by R=an,2.

Number of electrons produced in a Utit voltumiie of gas each second.

Intensity and directioni cosines of earth's nlagnietic fiel(l.

Highest frequency reflected by ionospheric region at vertical iincidence.

TABLE IVADDITIONAL PARAMETERS FOR THE MEVITEOROLOGICAL ATMOSPHERE

Meteorological Parameter

17C) Vector wind

18C) Vector current

19C) Energy spectrum of turbulent cellEd Ad

20C) Horizontal pressure gradient

21C) Onset-of-diffusion altitude

Description

Speed and direction of mass ImlotioIl of air.

Direction and currenit (leilsity of ionospheric electric current.

Energy content per uLit volume associated with cells of diamiieter betweeni d andd+Ad.

Rate at which pressure at fixed altitude varies with changes in latittude and lonlgi-tude.

Altitude at which diffuision rather thani mzixing begins to determinie atmosphericcomposition.

TABLE VPARAMETERS FOR "ENEFRGY BALANCE" ATMOSPHERE

"Energy Balance" Parameters

22D) Solar energy spectrum E(X) -AX

23D) Electron energy flux J(E) -AE

24D) Proton energy flux I(E) -AE

25D) Volume radiant energy input(X) * AX

26D) Volume electron flux energy inputj(E) *AE

27D) Volume proton flux energy inputi(E) *AE

28D) Volume energy input due to heatconduction

29D) Volume energy input due to chem-ical reaction

30D) Volume energy input due to elec-tric currents and hydromagneticwaves

31 D) Optical depth

Description

Energy flow from sUnI per unit area in wavelength band between X and X+AX.

Energy flux per unit area conitainied in electronis of energy between E and E+AE.

Energy flux per unit area conitained iln protons of energy between E and E+AE.

Net increase in energy per unit volume due to excess of radiation absorption overemission for radiation between X and X+AX. E(X) is negative in thermal region ofinfrared.

Energy input per UInit volume due to passage through volume of electrons of en-ergy between E and E+AE.

Same as 26D), but for protons.

Net increase in energy per unit volume due to excess rate of heat coInduction1 inltovolume over rate of heat conduction out of volume.

Net increase in energy per unit volume due to excess rate of production of heat bychemical reaction over rate of heat loss by chemical reaction.

Energy per unit volume dissipated by ohmic current loss.

Natural logarithm of ratio of flux incident at top of atmosphere to flux incident ataltitude h. Optical depth is a function of wavelength.

Units

degree

degree

1seC -- '

(1113 SeC-1

('111-3 se(' I

Gauss

sec---

I

li

('111 seC

ampere (-1II 2

erg cm --3

dvIe ( -1

c(

ItTllIt

erg cnm-2 sec I

erg C m-2 sec

erg (c-I2 seC

erg cmil-3 sec- I

erg c(-13 sec --I

erg cm-3 sec-'

erg ('1-3 se-'

erg c(mn3 sec~-

erg cm- sec

pure number

2200 No7vcmber

Bates: Detection and Identification of Nuclear Explosions Underground

levels at which strong atmospheric turbulence takesplace providing good atmospheric mixing. This dynamicatmosphere might be called the "meteorological" at-mosphere, and some of the parameters which might beused to define it are listed in Table IV. The measurementof wind profiles is vital to a description of the meteoro-logical atmosphere. Here the main tool has been the useof triangulation on sodium or other artificial vapor trails,illuminated generally by sunlight. Triangulation of per-sistent luminous meteor trails or tracking of meteor ionclouds and ionospheric irregularities by radar and radioreflection techniques are other means by which the upperair wind system is studied. Current sheets are studiedby use of magnetometers. Ground magnetic measure-ments are used to plot the current systems on a globalscale. Rocket-borne magnetometers locate the height,direction and strength. of individual current sheets.

There is one additional model of the atmospherewhich will be described. This model we will call the"energy balance" atmosphere. The properties of theupper atmosphere are, to a considerable extent, deter-mined by the rate and mechanisms by which energy ispoured into the atmosphere by means of incident sun-light and particles, and by the rate and mechanisms bywhich this energy is eventually radiated away into spaceor conducted to cooler atmospheric layers. The rate atwhich energy is contributed to the atmospheric fluid isdetermined both by the radiation and particle field in-cident on the fluid and also by the opacity of the gas

under irradiation; in other words, if the gas does notabsorb or alter any of the incident radiation, it is un-affected by it. Some of the instrumentations used instudying the "energy balance" atmosphere include farultraviolet optical spectrographs and photometers forstudy of the incident solar radiation flux; particlecounters and ion chambers for study of incident particleradiation; photomultiplier photometers and air glowcameras and spectrographs for study of visible air glowand auroral emissions; and balloon and rocket-borne in-frared spectrometers for study of thermal and photo-chemical emissions from the air. Hydromagnetic waveanalyzers may also be of use to determine whether suchwaves cause any noticeable heat input to the upper air.Table V includes a tabulation of some of the key addi-tional parameters needed in defining the "energy bal-ance" atmosphere.As the reader can see, the various methods of de-

scribing the upper atmosphere are interrelated. No oneview completely defines all aspects of the geophysicalmedium under study. The viewpoints listed certainly donot include all the properties which one would like toknow, but they provide an adequate set to give a goodgeneral description of the upper air. The particular setsof parameters listed are not necessarily those whichothers would choose, but they do constitute a sufficientlycomplete list that a good proportion of the other parame-ters of interest can be calculated from them and fromconstants measurable on the ground.

Detection and Identification of Nuclear ExplosionsUnderground (Project VELA UNIFORM)*

CHARLES C. BATESt

Summary-Project VELA UNIFORM is part of a broad researchprogram designed as the first full-fledged national effort for develop-ing a specific type of arms control technology. Based on earth scienceresearch, the VELA UNIFORM effort is directed towards obtaininga suitable system for the detection, identification and location ofnuclear explosions underground in support of a possible nuclear testban. The principal work areas are classical and explosion seismology,the development of suitable field equipment and prototype observa-tories and data centers, and the conduct of an extensive monitoringprogram of seismic and other unique signatures from the presentU. S. series of subsurface nuclear detonations.

* Received September 17, 1962.t Nuclear Test Detection Office, Advanced Research Projects

Agency, Department of Defense, Washington, D.C.

INTRODUCTION

O OON AFTER the beginning of nuclear test ban3 negotiations in 1958, it became apparent that a

better technical basis for the detection and identifi-cation of nuclear explosions underground and in spaceby use of remote sensors must be developed. Within theDepartment of Defense, the Advanced Research Proj-ects Agency was assigned the responsibility for theproject now known by the code name VELA. Thisproject was further divided into three parts: VELAUNIFORM, which deals with underground detonationsand ground-based detectors, VELA SIERRA, which is

1962 2201