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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 COllcel·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 allky 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.£ 89 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 220

Comments on a paper "Auroral Sporadic-E Ionization" by Robert D. Hunsucker and Leif Owren.