JOURNAL OF RESEARCH of the National Burea u of Sta ndards-D. Radio Propagation Vol. 67D, No.4, July- August 1963

Reply to 1. M. Bullen and G. A . M. King's JlComments on a Paper 'Auroral Sporadic-E Ionization' by Robert D. Hunsucker and Leif Owren"

Robert D. Hunsucker and Leif Owren

Contribution from Geophysical Institute, University of Alaska, College, Alaska

(Received J a nuary 28, 1963)

The comments of Bullen and King [1963] on the paper "Auroral Sporadic-E Ionization" by Hun­sucker and Owren [19 62] cover two main poin ts. The first point concerns questions of taxonomy in connection wi t h auroral-zone ionograms and the sec­ond, the rebtionship between zenithal auroral lumi­nosity and the thickness of the associated auroral E layer as indicated by ionosonde records.

With regard to the first point, our paper was COll­

cel·ned with the relationship of obser ved E top fre­q uencies to visual zenithal aurora, and defini tely not wi t h details of taxonomy. In fact, we st.ated tha t " The approach in t his paper is to study the radio refl ectin g properties of t he E layer , no tably as indicated by the value of fEs n,nd its variation , at times wh en the occurrence and degree of visual auror al activity is known from simultaneous observa­t ions withou t regard to classifi cation details. T lwre­fore we are co ncerned with the auroral sporadic E ionizat ion in the wider , physical sense rather than the restricted type designated by the too inclusive term Es-auroral. "

The term " :wroral sporadic E ionizaLion" was therefore used in a general way, including rather than excluding the "nigh t E" layer. The reason why the term "night E" does not appear anyvl here in the paper is simply that we have followed the

. practice of the National Bureau of Standards for r at least this auroral zone station in calling most

ni.ghttime E ionization seen on ionograms "sporadic E." The designations of the individual ionograms appearing in the figures 3 thro ugh 10 are those assigned by the local scaler according to the instruc­t ions received from the National Bureau of Standards.

Bullen and King are certainly justified in classify­ing most of these ionograms as "night E" if they so prefer , and want to use the term "sporad ic E" in a narrow sense. This part of their co mment is of value in demonstrating again the difficulties, includ­ing seman tic, involved in scaling and in terpreting auroral zo ne ionograms, as has been done before by many other investigators [see K. D avies, 1956]. But their taxonometric discu sion affects in no way our conclusion regardin g the relationship between observed E top frequency and zenithal aurora.

The second poin t raised by Bullen n,nd King co n­cerns the relation between the critical frequency of a "thick" ionospheric layer in the E region and the auroral luminosity. Their comment illustrates how easy i t is to overinterpret auro ral-zone soundin gs . On the basis of the ionogralll in figure 10 of our pn,per , they conclude that considerable a Uforallumi­nosity, in Lhe form of an overall glow, m.ust be pres­ent in t he sky, although we listed the all- ky camera record as showing " no auroral activity." Their con­clusio n is based on the work of Omholt [1955] and their own preliminary studies . Omholt found a cor­relatio n b etween pho ton emissio n wi thin the neo-a­t ive ni trogen band \4278 A) from 7.eni thnl aur~ra and the electron density of t he associated E layer. It should be noted that in an effort to deduce crit­ical frequencies at zeni th only , he sdected traces which showed mul tiple reflections from t he Ea layer or an F layer above the cri t ical frequency of th~ E a layer.

The history of auroral activiLy durin g the ni ght 0.£ 8- 9 D ecember 195 which we ded uced q ualita­tlvely from t he all-sky camera records, can be con­fll·m ed quantitatively from the simultaneous paLrol observations wi th the Huct spectrograph operated by Romick [1961] at College, Alaska, during IGY. 1~he .Huet spe.cLograph plate for Lhe night in ques­tlOn lS shown 10 figure 1, and Lhe spectrograph scale giving the time marks and wavelength calibration is shown in figure 2. It is apparen t that the nega­tive nitrogen line (4278 A) as well as the other lines in the auroral spectrum show maximum inten­sity between 2100 and 2200 1500 WMT corre pond­ing to the maximum. auroral activity indicated in the all-sky camer a pho tograph of flgure 9 in our paper . .At the time of the all-sky camera photo­graph in figure 10, Romick confirms from th e spectro­graphic record that Lhere was no visible auroral emission in the sky (private communication) . The change in the character of th e ionograms from fig­ure 9 to figure 10 should be noted and co mpared with Omholt's criteria.

Thus it appears that for the auroral display of - 9 D ecember 1958 the all-sky camera, spectro­

graphic and ionosonde data presented by the authors are in agreement with Omhol t's results but not with Bullen and King's interpretation of Omholt's results.

385

FIGUHE 1. I-Iuet spectJ'ograph plate fol' night of 8- 9 December 1958.

References

Bullcn, J. M ., and G. A. M. King [1963], Co mmcnts on a papcr 'Auroral sporadic-E ionization ' by Robcrt D. Hun­suckcr and Lcif OIl'1'en, J . R esearch N BS G7D (Radio Prop.), No.4. 383.

Davics, K. (1956), Solar eclipses in thc ionosp here, edited by Beynon and Brown , 45- 46 (Pcrgamon Prcss, London) .

Hunsucker, Robert D., and Lcif OWl'cn (1962), Au roral sporadic- E ionization, J . R esearch NBS GGD (Ra dio Prop.), No.5, 581- 592.

Omholt, A. (1955), The auroral E-Iayer ionization and the a uroral luminos ity, J . Atmospheric Ten·est. Ph ys. 7, 73- 79 .

Romi ck, G. J . (March, 1961), Catalogue of Huet auroral spectra 1957- 1958, Scicnt ific R cport No.1, Geophysical Institutc of the Uni ve rsity of Alaska.

386

NIl 01 5003 NI 5577 6300

3914 Hg1 IHg 4278 Hg Nz NEG 4709 H/l I 5200 Hg I HgNo II Ho N2 1ST POS. r--t+----"r-+I -=-------'-' ")) I I I I I km

4000 ! I ! I t I I I I I II IIIII!!!!!!!!

4500 5000 5500 6000 6500

FIGURE 2. Scale for l-I1Wt spectrograph plate.

0800

0600

0400

0200

,....: ::i

0000 ~ .,.,

2200

2000

1800

1600

(Paper 67D4- 273)