- Email: [email protected]
COSPAR workshop on the IRI
Adv. Space Res.
Vol. 5, No. 10, pp. 3—7, 1985 Printed in Great Britain. All rights reserved.
0273—1177/85 $0.00 + .50 Copyright ~ COSPAR
HIGHLIGHTS OF THE 1985 URSI/ COSPAR WORKSHOP ON THE IRI Y. V. Ramanamurty* National Physical Laboratory, Hillside Road, New Delhi-110 012, India
ABSTRACT Some of the presentations made at the IRI Workshop held at Louvain in 1985 have not appeared in the Proceedings. Some discussions which took place during the workshop could be of interest in future work. This article tries to highlight the IRI modelling aspects in the four principal height regions of the ionosphere. INTRODUCTION The opening of the workshop began with a welcome address followed by felici— tations to Prof. 1. Bossy on the eve of his retirement and in honour of his getting Emeritus Professorship (the first of its kind at Universit~ Catho— lique, Louvain—La-Neuve, Belgium). The external inputs into the International Reference Ionosphere (IRI) were discussed /1/. The station—oriented Gallet— Jones approach of numerical mapping as accepted by OCIR is used in all prediction services. Since there are not enough stations in oceans and the global coverage other than in Europe and USA is inadequate, URSI created a panel on numerical mapping to look for a better system. The synthesis with data obtained from. space is quite difficult. With satellite data, it is difficult to reproduce the diurnal variation and a limited height range (2oo km)is accessible. Danilov has arranged several rocket campaigns for ion composition measurements below 2oo km, expecially for the IRI. Two AEROS satellites were launched largely for gathering data suitable for the IRI. The existing data collected at the northern mid—latitudes, has to be adopted to the southern hemisphere and the oceans. In the IRI description, the relative percentage of the different ion species is needed. Unfortunately, most satellite data give absolute ion densities only. The interest of information obtained by incoherent scatter techniques was stressed by Rawer /2/. There are quite a few problems when conventional iono— sonde measurements are used for modelling the electron density distribution Ne(h) in the ionosphere. Sometimes it is difficult to combine these data with the satellite data. The specific technique of incoherent scatter (ISC) might be used for checking. Unfortunately, the coverage of ISC data is poor in space and time. The longest time series of data available at Millstone Hill is statistically less significant than the monthly means from the ionosonde n~etwork.A few days data may not be representative to get a monthly mean. The lunar tides are not reflected in the ISO data. Previously, the E—region was not reproduced. But now, it is being probed and the E—F valley region too. With the ionosonde technique, the P2—peak is not really measured but extrapolated. The ISO technique depends on local density and, hence, is quite useful in this context. Regarding the topside data base, Bent’s ALOUETTE analysis based upon about lo.ooo ionograms applies a discontinuous scheme in latitude. This was made continuous by Ramakrishnan and was checked with ISO data. Recent studies in U.K. (which could be of interest to the IRI modelling effort), using various experimental facilities such as EISOAT and the coherent scatter method, probing the magnetosphere by electro-magnetic waves and the influence of the ionosphere on radio systems were reported by Bradley /3/. He pointed out that one might use ionospheric models (such as the IRI model) to calculate the bearing errors. Bibi /4/ noted the importance of taking into 3
4
Y. V. Ramanamurty
account the geographical/longitudinal variability of the P2—peak parameters. He also mentioned that lo and 9o% confidence limits to the peak parameters would greatly help the user community. Bilitza /5/ presented a theoretical approach and compared it with the data-based approach of IRI to model the plasma parameters Ne, T~. It was felt that semi-empirical approaches might be helpful in connection with IRI, but only in situations where the data base is not sound. LOWER IONOSPHERE The input from the station—oriented radio observations and its assimilation into the new formula for the International Reference Lower Ionosphere (IRLI) was discussed by Ramanarnurty /6/. Moraitis /7/ compared the partial reflection and cross modulation profiles of electron density with the IRI—79. The techniques are reported to be sensitive between 7o and 9o km~a region which is however better explored by rockets. Serafimov and Serafimova/8/ compared the Al and A3 absorption measurements with the IRI description using approximate formulae for calculating the absorption. A more sophisticated approach might be needed so as to provide an input to the IRI. Barbatsi /9/ described an observation of fine structure in the diurnal variation of foE during a magnetically disturbed period. Power spectral analysis of hmE also showed signigicant fine structure. The work of Velinov and Gerdjikova /lo/, dealing with the ion pair production rate due to high energy solar particles, was presented by Prof. Serafimov. Bain/ll/ presented electron density models consistent with the vif/if observations in U.K. He agreed that unique results cannot be obtained using the vlf/lf data alone. In order to reduce the variations in the ionosphere, he only used rather short distance data. Phase (relative to the ground wave) and amplitude measurements were carried out simultaneously. He mentioned of seasonal variation in the Ne(h) profile not related to the solar zenith angle alone. Considerable variability of the profile in winter is reported. A summary of the discussion on modelling the lower ionosphere for the IRI appears elsewhere in this issue /12/. The question of what to take as ‘noise’ for the purposes of the IRI, the accountability of the observation on Schumann resonances and the incorporation of latitudinal dependence (other than % ) were raised by Rycroft /13/. Taubenheim /14/ made a brief presentation on a possible deduction of the transition level (where the cluster ions begin to dominate) in the D—region based on semi—empirical considerations. The approach makes use of the CIRPi linked temperature and assumptions on the magnitude of the water vapor mixing ratio (where a large uncertainty factor exists in view of its strong dependence on temperature). The chemistry of the D-region is known to be very complex. Any attempt to simplify would result in significant departure from .the actual situation. It would, therefore, appear more reasonable to read the transition level directly from the available (although few in number) measurements on the positive ion composition in the D—region. TOPSIDE IONOSPHERE Bilitza /15/ reported on the construction of the IRI profile of electron density Ne(h) for the equatorial topside. Oalculation of total electron content (TEO) is needed for satellite tracking facilities, mostly close to the equator. McNamara compared the IRI N~ Model with the measurements and found good agreement at middle and high latitudes but severe underestimate at low latitudes. The topside data base due to Bent has been combined with the ISO and satellite (AEROS) data. Recently, the too flat descriptions of the topside at low latitudes was revised resulting in better agreement of IRI with the observations in the equatorial zone (32 ranges in latitude were considered). The question of modelling the plasmasphere on top of the IRI was proposed many years ago by Rycroft /13/. Although the IRI attempts to model the ionosphere in a vertical direction, it is certainly adequate to model the plasmasphere along the magnetic field lines. The question of matching adjacent IRI profiles at the two points of intersection (at heights between 3oo and 9oo km) comes up. An exponential distribution of Ne(h) together with an Epstein step function for matching the adjacent profile descriptions through the transition height were agreed upon. The compatibility of electron temperature and ion composition with a diffusive equilibrium model (Rycroft and Alexander model) and the IRI description of these quantities was also discussed. Bilitza /16/ made a comparison of measured and predicted P2—peak altitude hm
Highlights
5
with the various descriptions in the literature (model descriptions due to Becker, Nisbeth, Ohiu, Shimazaki, Bradley and Dudeney, Eyfrig , BilitzaEyfrig-Sheikh). Using a more extensive data base, the correction term proposed earlier by Bilitza, Eyfrig and Sheikh for the noon—time is applied to the whole day. In the discussion of Bycroft’s proposal/13/ it was agreed that when modelling the plasmasphere the trigonometric (cos) functionshould be replaced by E~— stein step, that the interpolation across the equator must be checked and that the TEC data gathered at several places should be used for verification. MIDDLE IONOSPHERE The determination of electron density profiles for the middle ionosphere was presented by Rawer /17/. Use of 3 or 4 LAY functions is envisaged depending on the complexity of the profile. As a measure of the matching criterion, the reduced mean square error (with low weight below a lower limit of -‘~1oo km) is used. Since heights and amplitudes are narrowly connected, repeated function evaluations rather than calculation of derivatives are u.ged in the fitting procedure to make the error sum minimum. An error diagram showing the contours of constant error is helpful to find out which parameters are not independent. The procedure is illustrated using ionosonde data and Becker’s rather sophisticated method of reduction. One (main) LAY function controls the main shape and the other (2 or 3) LAY functions are used to shape characteristic features of the profile. About 2o—3o profiles from Becker’s collection (which do not normally show a valley) are used to get median values of the non-linear parameters HX and SO (the ‘transition heights’ and ‘scales’). Anderson et al. /18/ described a Semi-empirical Low Latitude Ionospheric Model (SLIM). The method is based on obtaining time dependent solution of the continuity equation taking account of the E~Bdrift and assuming cfrto be the major ion. The final description can be summarized by a Chapman-like equation of the form Ne(h) = Nm exp(c(1 — z exp(—z))) z
=
(h
-
hm)/A
with Nm and hm, the physical~ak parameters, and c and A different above and below the peak, thus 6 coefficients in all. At the equator, a rather high value of 450 km for HmP2was reported. This value appears to be consistent with the M(3000) data. It was mentionned that introduction of longitudinal variation, zonal winds and higher latitude electric field might be needed. The model is expected to hold good within ±24°la— titude zone around the equator and up to a height of about 25oo km. Serafimov /19/ wondered about the applicability of a M(3ooo)/HmP relationship at low latitudes. It is suggested to make a check by computing the virtual height from the true height profile and then scaling the M(3ooo) factor. Paul /2o/ dealt with the variability of the peak parameters due to off—vertical sounding which occurs quite often. He mentionned that the short term variations observed in MTJP(3ooo) are real, but often not in agreement with those of foP2. He showed examples where within about 14 minutes, large changes in virtual height are observed. His conclusion is that rather large errors in determining hmP cannot be avoided in profile analysis from lonograme. He recommends the use of hp also in the statistical relationships relating the peak density and height parameters, to give less weight for data collected during disturbed periods. Rawer remarked that much of the variability reported by Paul is ‘noise’, so far as IRI is concerned and inquired about better(statistical) investigations to obtain hmF2 by different techniques without using M(3000). hp might help if it is scaled from the ionograms regularly and this could lead to a good alternative to the Shimazaki equation. Serafimov /21/ presented relatlons showing the longitudinal asymetry in the diurnal variation of electron and ion density distributions in terms of the magnetic dip coordinate. Rawer noted the necessity of accounting the differences with the OCIR description as well.and for improved relationships connecting M(3000) and hmP2. The use of the solar zenith angle or the ]ocal time for interpolation purposes (within the IFtI computer program) was briefly presented by Ramanamurty /22/. K. Bibi also mentionned the network of digisondes currently in operation co—
6
Y. V. Ramanamurty
vering half the longitude zone of the Earth. The data is being collected in a usable format and for true height analysis in real time. A microcomputer can handle the operation and data reduction. Both, the ordinary and extraordinary components, are needed for the analysis with an accuracy of lo km (separation) and the minimum virtual heights to 1 km accuracy. The data is expected to result in improvement of radio propagation studies and can form an input to the IRI. The data revealed that equatorial ionograms are basically different from the mid—latitude ones, shifted both in time and frequency. The valley depth up to 2o% is believed to be inferred and this shall be a good contribution from this technique. which can obtain both, the amplitude and phase ionogram, the frequency increment being 15 kHz/23/. Bilitza /24/ reported on the mission-oriented models of electron temperature Te (e.g. Spenner and Plugge, Brace and Theis) in the construction of the IRI model of Te between loo to boo km. Five Epstein transitions were used to model Te in this region. Koleva /25/ presented the Intercosmos—Bulgaria—l3oo satellite observations on the ion composition referring to the 450 to 88o km height region. The IRI—79 description on the ion composition in the equatorial region is reported to be opposite to the observed features. FINAL DISCUSSION AND FUTURE PLANS The new official version of the IRI description is yet to be accepted by URSI/OOSPAR. In the meantime, the interim computer program (with an improved temperature and topside description) shall be sent to each Member of the Task Group. The results of the low latitude mode].shall becomniunicated by Dr. Anderson and Dr. Bibi to Dr. Bilitza, who is now with the Ooddard Space Flight Center (U.S.A.). Dr. Rycroft shall be rearranging his proposal to model the plasmasphere along the guidelines agreed upon, i.e. use of hmF instead of 3oo km, Epstein function instead of cosine, the transition height involving the sliding fit (65o km) could be made variable. We then have four height ranges demarcated by hxnE, hmF and the 65o km level. Geophysically based relations would be established to determine the amplitudes of the LAY functions. The use of characteristic points, such as 0.8 hmP suggested by Gulyaeva in the P-region modelling work is recommended. An alternative could be the use of lip (at o.833foP2). The data base on Ne(h) profiles for the lower ionosphere till the end of 1977 was made computer accessible by McNamara /27/. Efforts are to be made to collect the subsequent measurements. The use of appropriate value (based on observational evidence) for hmF is recommended. A summary of the Louvain-LaNeuve—Workshop on IRI was circulated /26/ to the Members of the IRI Task Group. REFERENCES 1.
K. Rawer, About the International Reference Ionosphere, Inauguration speech to the Workshop
2.
K. Rawer and D. Bilitza, The interest of information obtained by incoherent scatter technique, this issue
3.
P. Bradley, Recent studies of interest to IRI in UK, oral presentation
4.
K. Bibl, oral presentation
5.
D. Bilitza, Heat balance of the ionosphere: implications for the
6.
International Reference Ionosphere, this issue Y.V. Ramanamurty, Input from station—oriented radio observations and its assimilation into the new formula for the International Reference Lower Ionosphere (IBM) model, this issue
7.
G. ?4oraitis, Comparison between. D— and lower E-region electron density profiles and IRI, this issue
8.
K.B. Serafimov, M.K. Serafimova, Y.V.”Ra.manaxnurty and K. Rawer, A note on the use of absorption measurements for improving the IRI electron density distribution in the lower ionosphere, this issue
Highlights
7
9.
O.K. Barbatsi, A study of the short—term variation of foE during a sudden magnetically disturbed period, this issue
lo.
P. Velinov and M. Gerdjikova, Normalized electron production rate profiles as a result of penetration of high energy solar particles into the lower ionosphere, this issue
11.
W.C. Bain, Electron density models for the lower ionosphere, this issue
12.
Y.V. Ramanamurty, Report on the discussion on modelling the lower ionosphere, this issue
13.
M.J.Rycroft and I.R. Jones, Modelling the plasmasphere for the Inter-
14.
national Reference Ionosphere, this issue J. Taubenheim, On the incorporation of the cluster ion transition level in the D—region, oral presentation
15.
D. Bilitza, Electron density in the equatorial topside, this issue
16.
D. Bilitza, Comparison of measured and predicted P2—peak altitude, this issue
17.
K. Rawer, Determining electron density profiles for the middle ionosphere, this issue
18.
D.N. Anderson, N. Mendillo and B. Herniter, A semi—empirical, latitude ionospheric model, to be published elsewhere
19.
K.B. S~rafimov, Proposal for the improvement of the electron density profile in the F—region, this issue
2o.
A.K. Paul, Reliability of electron density profiles, this issue
21.
K.B. Serafimov, I.S. Kutiev and Ts.P. Dachev, Latitudinal asymmetry in electron and ion density distribution in southern and northern hemispheres, this issue
22.
Y.V. Ramanamurty, Refinement in the diurnal variation of IRI—79 electron density distribution, this issue
23.
K. Bibl and N. Calandrella, Practical method for routine analysis of the valley parameters between E- and F-region of the ionosphere, this issue
24.
D. Bilitza, Implementaion of the new electron temperature model in IRI, this issue
25.
Ft. Koleva and I.S. Kutiev, On the relative abundance of Helium ions in the topside ionosphere, this issue
26.
L. Bossy (chairman, IRI), Identification of problems and decisions, (Summary of the Louvain-La-Neuve-Workshop on IRI), Circular letter, December 1985
27.
L.F. McNamara, Ionospheric D—region data base, a collection of computer accessible experimental profiles of the D— and lower E—region, Report UAG-67, WDC-A, NOAA, Boulder,Co., U.S.A. (1978)
low
Vol. 5, No. 10, pp. 3—7, 1985 Printed in Great Britain. All rights reserved.
0273—1177/85 $0.00 + .50 Copyright ~ COSPAR
HIGHLIGHTS OF THE 1985 URSI/ COSPAR WORKSHOP ON THE IRI Y. V. Ramanamurty* National Physical Laboratory, Hillside Road, New Delhi-110 012, India
ABSTRACT Some of the presentations made at the IRI Workshop held at Louvain in 1985 have not appeared in the Proceedings. Some discussions which took place during the workshop could be of interest in future work. This article tries to highlight the IRI modelling aspects in the four principal height regions of the ionosphere. INTRODUCTION The opening of the workshop began with a welcome address followed by felici— tations to Prof. 1. Bossy on the eve of his retirement and in honour of his getting Emeritus Professorship (the first of its kind at Universit~ Catho— lique, Louvain—La-Neuve, Belgium). The external inputs into the International Reference Ionosphere (IRI) were discussed /1/. The station—oriented Gallet— Jones approach of numerical mapping as accepted by OCIR is used in all prediction services. Since there are not enough stations in oceans and the global coverage other than in Europe and USA is inadequate, URSI created a panel on numerical mapping to look for a better system. The synthesis with data obtained from. space is quite difficult. With satellite data, it is difficult to reproduce the diurnal variation and a limited height range (2oo km)is accessible. Danilov has arranged several rocket campaigns for ion composition measurements below 2oo km, expecially for the IRI. Two AEROS satellites were launched largely for gathering data suitable for the IRI. The existing data collected at the northern mid—latitudes, has to be adopted to the southern hemisphere and the oceans. In the IRI description, the relative percentage of the different ion species is needed. Unfortunately, most satellite data give absolute ion densities only. The interest of information obtained by incoherent scatter techniques was stressed by Rawer /2/. There are quite a few problems when conventional iono— sonde measurements are used for modelling the electron density distribution Ne(h) in the ionosphere. Sometimes it is difficult to combine these data with the satellite data. The specific technique of incoherent scatter (ISC) might be used for checking. Unfortunately, the coverage of ISC data is poor in space and time. The longest time series of data available at Millstone Hill is statistically less significant than the monthly means from the ionosonde n~etwork.A few days data may not be representative to get a monthly mean. The lunar tides are not reflected in the ISO data. Previously, the E—region was not reproduced. But now, it is being probed and the E—F valley region too. With the ionosonde technique, the P2—peak is not really measured but extrapolated. The ISO technique depends on local density and, hence, is quite useful in this context. Regarding the topside data base, Bent’s ALOUETTE analysis based upon about lo.ooo ionograms applies a discontinuous scheme in latitude. This was made continuous by Ramakrishnan and was checked with ISO data. Recent studies in U.K. (which could be of interest to the IRI modelling effort), using various experimental facilities such as EISOAT and the coherent scatter method, probing the magnetosphere by electro-magnetic waves and the influence of the ionosphere on radio systems were reported by Bradley /3/. He pointed out that one might use ionospheric models (such as the IRI model) to calculate the bearing errors. Bibi /4/ noted the importance of taking into 3
4
Y. V. Ramanamurty
account the geographical/longitudinal variability of the P2—peak parameters. He also mentioned that lo and 9o% confidence limits to the peak parameters would greatly help the user community. Bilitza /5/ presented a theoretical approach and compared it with the data-based approach of IRI to model the plasma parameters Ne, T~. It was felt that semi-empirical approaches might be helpful in connection with IRI, but only in situations where the data base is not sound. LOWER IONOSPHERE The input from the station—oriented radio observations and its assimilation into the new formula for the International Reference Lower Ionosphere (IRLI) was discussed by Ramanarnurty /6/. Moraitis /7/ compared the partial reflection and cross modulation profiles of electron density with the IRI—79. The techniques are reported to be sensitive between 7o and 9o km~a region which is however better explored by rockets. Serafimov and Serafimova/8/ compared the Al and A3 absorption measurements with the IRI description using approximate formulae for calculating the absorption. A more sophisticated approach might be needed so as to provide an input to the IRI. Barbatsi /9/ described an observation of fine structure in the diurnal variation of foE during a magnetically disturbed period. Power spectral analysis of hmE also showed signigicant fine structure. The work of Velinov and Gerdjikova /lo/, dealing with the ion pair production rate due to high energy solar particles, was presented by Prof. Serafimov. Bain/ll/ presented electron density models consistent with the vif/if observations in U.K. He agreed that unique results cannot be obtained using the vlf/lf data alone. In order to reduce the variations in the ionosphere, he only used rather short distance data. Phase (relative to the ground wave) and amplitude measurements were carried out simultaneously. He mentioned of seasonal variation in the Ne(h) profile not related to the solar zenith angle alone. Considerable variability of the profile in winter is reported. A summary of the discussion on modelling the lower ionosphere for the IRI appears elsewhere in this issue /12/. The question of what to take as ‘noise’ for the purposes of the IRI, the accountability of the observation on Schumann resonances and the incorporation of latitudinal dependence (other than % ) were raised by Rycroft /13/. Taubenheim /14/ made a brief presentation on a possible deduction of the transition level (where the cluster ions begin to dominate) in the D—region based on semi—empirical considerations. The approach makes use of the CIRPi linked temperature and assumptions on the magnitude of the water vapor mixing ratio (where a large uncertainty factor exists in view of its strong dependence on temperature). The chemistry of the D-region is known to be very complex. Any attempt to simplify would result in significant departure from .the actual situation. It would, therefore, appear more reasonable to read the transition level directly from the available (although few in number) measurements on the positive ion composition in the D—region. TOPSIDE IONOSPHERE Bilitza /15/ reported on the construction of the IRI profile of electron density Ne(h) for the equatorial topside. Oalculation of total electron content (TEO) is needed for satellite tracking facilities, mostly close to the equator. McNamara compared the IRI N~ Model with the measurements and found good agreement at middle and high latitudes but severe underestimate at low latitudes. The topside data base due to Bent has been combined with the ISO and satellite (AEROS) data. Recently, the too flat descriptions of the topside at low latitudes was revised resulting in better agreement of IRI with the observations in the equatorial zone (32 ranges in latitude were considered). The question of modelling the plasmasphere on top of the IRI was proposed many years ago by Rycroft /13/. Although the IRI attempts to model the ionosphere in a vertical direction, it is certainly adequate to model the plasmasphere along the magnetic field lines. The question of matching adjacent IRI profiles at the two points of intersection (at heights between 3oo and 9oo km) comes up. An exponential distribution of Ne(h) together with an Epstein step function for matching the adjacent profile descriptions through the transition height were agreed upon. The compatibility of electron temperature and ion composition with a diffusive equilibrium model (Rycroft and Alexander model) and the IRI description of these quantities was also discussed. Bilitza /16/ made a comparison of measured and predicted P2—peak altitude hm
Highlights
5
with the various descriptions in the literature (model descriptions due to Becker, Nisbeth, Ohiu, Shimazaki, Bradley and Dudeney, Eyfrig , BilitzaEyfrig-Sheikh). Using a more extensive data base, the correction term proposed earlier by Bilitza, Eyfrig and Sheikh for the noon—time is applied to the whole day. In the discussion of Bycroft’s proposal/13/ it was agreed that when modelling the plasmasphere the trigonometric (cos) functionshould be replaced by E~— stein step, that the interpolation across the equator must be checked and that the TEC data gathered at several places should be used for verification. MIDDLE IONOSPHERE The determination of electron density profiles for the middle ionosphere was presented by Rawer /17/. Use of 3 or 4 LAY functions is envisaged depending on the complexity of the profile. As a measure of the matching criterion, the reduced mean square error (with low weight below a lower limit of -‘~1oo km) is used. Since heights and amplitudes are narrowly connected, repeated function evaluations rather than calculation of derivatives are u.ged in the fitting procedure to make the error sum minimum. An error diagram showing the contours of constant error is helpful to find out which parameters are not independent. The procedure is illustrated using ionosonde data and Becker’s rather sophisticated method of reduction. One (main) LAY function controls the main shape and the other (2 or 3) LAY functions are used to shape characteristic features of the profile. About 2o—3o profiles from Becker’s collection (which do not normally show a valley) are used to get median values of the non-linear parameters HX and SO (the ‘transition heights’ and ‘scales’). Anderson et al. /18/ described a Semi-empirical Low Latitude Ionospheric Model (SLIM). The method is based on obtaining time dependent solution of the continuity equation taking account of the E~Bdrift and assuming cfrto be the major ion. The final description can be summarized by a Chapman-like equation of the form Ne(h) = Nm exp(c(1 — z exp(—z))) z
=
(h
-
hm)/A
with Nm and hm, the physical~ak parameters, and c and A different above and below the peak, thus 6 coefficients in all. At the equator, a rather high value of 450 km for HmP2was reported. This value appears to be consistent with the M(3000) data. It was mentionned that introduction of longitudinal variation, zonal winds and higher latitude electric field might be needed. The model is expected to hold good within ±24°la— titude zone around the equator and up to a height of about 25oo km. Serafimov /19/ wondered about the applicability of a M(3ooo)/HmP relationship at low latitudes. It is suggested to make a check by computing the virtual height from the true height profile and then scaling the M(3ooo) factor. Paul /2o/ dealt with the variability of the peak parameters due to off—vertical sounding which occurs quite often. He mentionned that the short term variations observed in MTJP(3ooo) are real, but often not in agreement with those of foP2. He showed examples where within about 14 minutes, large changes in virtual height are observed. His conclusion is that rather large errors in determining hmP cannot be avoided in profile analysis from lonograme. He recommends the use of hp also in the statistical relationships relating the peak density and height parameters, to give less weight for data collected during disturbed periods. Rawer remarked that much of the variability reported by Paul is ‘noise’, so far as IRI is concerned and inquired about better(statistical) investigations to obtain hmF2 by different techniques without using M(3000). hp might help if it is scaled from the ionograms regularly and this could lead to a good alternative to the Shimazaki equation. Serafimov /21/ presented relatlons showing the longitudinal asymetry in the diurnal variation of electron and ion density distributions in terms of the magnetic dip coordinate. Rawer noted the necessity of accounting the differences with the OCIR description as well.and for improved relationships connecting M(3000) and hmP2. The use of the solar zenith angle or the ]ocal time for interpolation purposes (within the IFtI computer program) was briefly presented by Ramanamurty /22/. K. Bibi also mentionned the network of digisondes currently in operation co—
6
Y. V. Ramanamurty
vering half the longitude zone of the Earth. The data is being collected in a usable format and for true height analysis in real time. A microcomputer can handle the operation and data reduction. Both, the ordinary and extraordinary components, are needed for the analysis with an accuracy of lo km (separation) and the minimum virtual heights to 1 km accuracy. The data is expected to result in improvement of radio propagation studies and can form an input to the IRI. The data revealed that equatorial ionograms are basically different from the mid—latitude ones, shifted both in time and frequency. The valley depth up to 2o% is believed to be inferred and this shall be a good contribution from this technique. which can obtain both, the amplitude and phase ionogram, the frequency increment being 15 kHz/23/. Bilitza /24/ reported on the mission-oriented models of electron temperature Te (e.g. Spenner and Plugge, Brace and Theis) in the construction of the IRI model of Te between loo to boo km. Five Epstein transitions were used to model Te in this region. Koleva /25/ presented the Intercosmos—Bulgaria—l3oo satellite observations on the ion composition referring to the 450 to 88o km height region. The IRI—79 description on the ion composition in the equatorial region is reported to be opposite to the observed features. FINAL DISCUSSION AND FUTURE PLANS The new official version of the IRI description is yet to be accepted by URSI/OOSPAR. In the meantime, the interim computer program (with an improved temperature and topside description) shall be sent to each Member of the Task Group. The results of the low latitude mode].shall becomniunicated by Dr. Anderson and Dr. Bibi to Dr. Bilitza, who is now with the Ooddard Space Flight Center (U.S.A.). Dr. Rycroft shall be rearranging his proposal to model the plasmasphere along the guidelines agreed upon, i.e. use of hmF instead of 3oo km, Epstein function instead of cosine, the transition height involving the sliding fit (65o km) could be made variable. We then have four height ranges demarcated by hxnE, hmF and the 65o km level. Geophysically based relations would be established to determine the amplitudes of the LAY functions. The use of characteristic points, such as 0.8 hmP suggested by Gulyaeva in the P-region modelling work is recommended. An alternative could be the use of lip (at o.833foP2). The data base on Ne(h) profiles for the lower ionosphere till the end of 1977 was made computer accessible by McNamara /27/. Efforts are to be made to collect the subsequent measurements. The use of appropriate value (based on observational evidence) for hmF is recommended. A summary of the Louvain-LaNeuve—Workshop on IRI was circulated /26/ to the Members of the IRI Task Group. REFERENCES 1.
K. Rawer, About the International Reference Ionosphere, Inauguration speech to the Workshop
2.
K. Rawer and D. Bilitza, The interest of information obtained by incoherent scatter technique, this issue
3.
P. Bradley, Recent studies of interest to IRI in UK, oral presentation
4.
K. Bibl, oral presentation
5.
D. Bilitza, Heat balance of the ionosphere: implications for the
6.
International Reference Ionosphere, this issue Y.V. Ramanamurty, Input from station—oriented radio observations and its assimilation into the new formula for the International Reference Lower Ionosphere (IBM) model, this issue
7.
G. ?4oraitis, Comparison between. D— and lower E-region electron density profiles and IRI, this issue
8.
K.B. Serafimov, M.K. Serafimova, Y.V.”Ra.manaxnurty and K. Rawer, A note on the use of absorption measurements for improving the IRI electron density distribution in the lower ionosphere, this issue
Highlights
7
9.
O.K. Barbatsi, A study of the short—term variation of foE during a sudden magnetically disturbed period, this issue
lo.
P. Velinov and M. Gerdjikova, Normalized electron production rate profiles as a result of penetration of high energy solar particles into the lower ionosphere, this issue
11.
W.C. Bain, Electron density models for the lower ionosphere, this issue
12.
Y.V. Ramanamurty, Report on the discussion on modelling the lower ionosphere, this issue
13.
M.J.Rycroft and I.R. Jones, Modelling the plasmasphere for the Inter-
14.
national Reference Ionosphere, this issue J. Taubenheim, On the incorporation of the cluster ion transition level in the D—region, oral presentation
15.
D. Bilitza, Electron density in the equatorial topside, this issue
16.
D. Bilitza, Comparison of measured and predicted P2—peak altitude, this issue
17.
K. Rawer, Determining electron density profiles for the middle ionosphere, this issue
18.
D.N. Anderson, N. Mendillo and B. Herniter, A semi—empirical, latitude ionospheric model, to be published elsewhere
19.
K.B. S~rafimov, Proposal for the improvement of the electron density profile in the F—region, this issue
2o.
A.K. Paul, Reliability of electron density profiles, this issue
21.
K.B. Serafimov, I.S. Kutiev and Ts.P. Dachev, Latitudinal asymmetry in electron and ion density distribution in southern and northern hemispheres, this issue
22.
Y.V. Ramanamurty, Refinement in the diurnal variation of IRI—79 electron density distribution, this issue
23.
K. Bibl and N. Calandrella, Practical method for routine analysis of the valley parameters between E- and F-region of the ionosphere, this issue
24.
D. Bilitza, Implementaion of the new electron temperature model in IRI, this issue
25.
Ft. Koleva and I.S. Kutiev, On the relative abundance of Helium ions in the topside ionosphere, this issue
26.
L. Bossy (chairman, IRI), Identification of problems and decisions, (Summary of the Louvain-La-Neuve-Workshop on IRI), Circular letter, December 1985
27.
L.F. McNamara, Ionospheric D—region data base, a collection of computer accessible experimental profiles of the D— and lower E—region, Report UAG-67, WDC-A, NOAA, Boulder,Co., U.S.A. (1978)
low