Implementation of a new characteristic parameter into the IRI sub-peak electron density profile

.:~;P~ZC.? l‘i~it-it~ed in i?.3~. Grcjt

9l~l94, 1983 V()L2, Britain. No.10, All pp.l right s reserved.

O273_l177/S3/1O0l9I04$O3.OO/~ Copyright © COSPA1~

IMPLEMENTATION OF A NEW CHARACTERISTIC PARAMETER INTO THE IRI SUB-PEAK ELECTRON DENSITY PROFILE T. L. Gulyaeva Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, U.S. S. R. Academy of Sciences, 142092, Troitsk, Moscow Region, U.S.S.R.

ABSTRACT The shape of electron density profile in the International Reference Ionosphere could be improved significantly if the height h and electron density Ng of the P region sub—peak inflexion point were ~ in the set of the profile standard parameters. To study variations of these important parameters, the N(h) analysis of the statistically—summarized lonograms at the latitudes of 40_80011 of the Eastern hemisphere has been carried out for the two—hours intervals of local time, three seasons (winter, equinox and summer) and two levels of solar activities characterized by Covington indices P 10 .~ = 100 and 200. It is shown that the paraTMgmost 0.5cases NmP2 via the peak meters of the inflexion point ‘can be expressed in parameters of the P2 layer as lIg = 0.8 bmP2 and INTRODUCTION Por the updating of the International Reference Ionosphere by employing real—time observations it is necessary to adopt a compatible set of parameters representing either data. The IRI syatem [1‚2 J involves some auch standard parameters. We propose that this set should be complemented with the values of height, density and slope at the inflexion points of Eh). This would allow to describe the complete profile by a unique system of Epstein transition functions so that the full profile is described by an analytical and everywhere differentiable function [3,4,5]. The position of the inflexion point in the regular shape of the sub—peak ionosphere can be obtained along with some other potentially standard parameters of 11(h) profile by the analysis of the vertical—incidence ionograms [61. In order to apply to an ionospheric model, those parameters should be statistically ~nmm~ized as has been done in [7].

Considering, however, that many parameters of the Eh) profile are mutually interrelated, en attempt has been made in this paper to express the parameters of the inflexion point via the peak parameters of the P2 layer. To validate such en approach, the study bas been carried out with a sufficiently representative

statistically

s~nmiarizedset

of data.

COMPARISON OP IRI WITh RESULTS 0F ANAlYSIS OP IONOGRAMS There are two alternatives in using the data of vertical—incidence (VI) sounding for the ionospheric modelling: first, an extensive 11(h) analysis of ionograma to provide a data base for global models as, for example, in [8~1;second, the statistical s1~~m~ries of the primary data of VI followed by calculations of monthly composite 11(h) profiles [9]. The next, higher level of summ*~izingthe VI observations involving both temporal and spatial parametrization is represented by the method of constructing the typical ionograma by expansion of experimental data of the VI network of stations in a series of natural orthogonal functions [10,11]. Considered below are results of calculations of Eh) profiles from the synoptic ionograms [ii] constructed from the VI observations during the 5 quiet days of the months of March, June, September and December, years 1958 and 1964, using the data from the regional network of stations listed in[ioJ at latitudes 40 to 80°N of the Eastern hemisphere. The calculations of 191

.

192

T.L. Gulyaeva

11(h) profiles were carried out using the procedure given in [12] with allowance for the unseen ionization. We calculated 360 N(h) profiles of the two—hourly local time blocks making 30 sets of the daily variability of quiet ionosphere at the latitudes of 40, 50, 60, 70 and 80°N a regional standard ionosphere for the three seasons (winter, equinox, summer) and the two levels of solar activities (P 200). frequencies The 4 points of h‘f 7=of 100 h‘ and on equal steps in in E and (an Pl ordinary layers and 7 vai~!zg~ the both P2 layer component only) which had been tabulated in [iii were complemented with the Interpolated values of h‘f in the cases when the frequencies step was greater than 0.3 MHz. —

As a result of calculations, the three characteristic pointa were derived from an 11(h) profile for each ionospheric layer: the begin and the end of an observed part of layer and the inflexion point within it • These data were compared wi~hthe model 11(h) profiles of the International Reference Ionosphere, IRI 11,2], the latter being fitted to the P2 layer peak values as obtained from the ionograni analysis. Some examples of the comparison are presented In Pigure 1 where an appreciable difference between the model and experimental profiles can be seen in many cases.

80N

~ ~‚ ~

~ ‚ø‘

•‘Çr.J

~

~

•.~‘

~g~:

~‚

.ç.~,

p.

~

•~2‘

•~••->~ ~

~ K~ ~

~

‚~-„

02 4~O2 4602

..

.~‘:.•

~

30(

1 0(

.

~

• .

k-‘-“~

•.i~•

4681D12O24~ t 11,

00

06

12

18

(HZ LT

Pig.1 Comparison of IRI (circles) with plamma frequency real height profile fw(h) from ionograma (eolid curves) under the equinox condi‘Cions at P10 .~ — 100 (above) and 7the bottom. ThreeThecharacteristic pointa (the begin, ‘hours indicated inflexion the end) of local the E,tué‘ Pl and P2 are layers are i2~‘ — 200and(below). pointed out at the experimental curves. —

As implied by the comparison made, the shape of a model electron density profile could be improved significantly if the P2 layer sub-peak inflexion point was entered into the model. In the absence of an Pl layer, only one auch point can be determined Instead of the two or three levels REP, HST and HZ used in the present lEI [1‚2]. The only inflexion point defines the electron density distribution between the minimum of the E—P valley and the peak of the P region. If, however, the P1—P2 stratification is present, it is necessary to include also the Pl layer peak as well as the inflexion point below this peak.

TRI Sub—Peak Electron Density Profile

193

RELATION BETWEEN THE INFLEXION POINT PARAMETERS ARD THE P2 LAYER PEAK VALUES Discrepancies between the model and experimental profiles are evidenced In Figure 2. Here the daily variability of the P2 layer sub—peak inflexion point values normalized to the respective peak parameters the m~~ritnum electron density Nm and the corresponding peak height hrn of the P region is shown. The inflexion point in IRI either occur at the level of HZ (as given by open circles in Figure 2) when the Pl layer is absent or coincides with the‘peak‘of the Fi layer (closed circles). Though the height of these levels in lEI differs slightly in many cases from the inflexion point height as revealed by the ionograms analysis (Figure 2 in the bottom), electron denaïty at these levels in lEI are far less than the values of 11g at the inflexion point of the experimental profile. —

-

WINTER

EQUINOX

~

o

SUMNER

V~-~‘~\-

80°

~

•°°°°‚••°°°°~=~°°‚° ..—.—....—..—.‚.••

~ ./t~__.__/—_- ~ ~

~

~

d‘~‘~

Œ5 ~ C ~e Jia,~th,

~

..•—.‚

6

e

‚•.‘.

o

~

0

f2

0

60° 40°

~ ~o

‚...—..—o..

12

•‘f ~

~‚

•

12

•‚

~rr 0 I2LT

~

02

80°

04

~

0.4

.

•~

~

„..•‚

F~: 400

s

.•..

°h~k~a

~‘1a~‘~

~

200

100

200

100

40° 200

Pig.2 Variation of the sub-peak inflexion point parameters in the P2 layer relative to main peak values of 11m12 and hmP2. Solid dotted curves the ionograma results, circles lEI calculations. Diurnal change of Ng/Nm (the top pert) end of (hrn hg)/hin (the bottom part) is shown for the three seasons, two levels of solar activities and three latitudes (40, 60 and 80°N). —

-

-

As one can see from Figure 2, the location of the inflexion point relative to the P2 layer peak remains essentially unchanged under all of the ionospheric conditions considered.A relation of parameters of these two characteristic points can be expressed roughly as hg

=

0.8 hmP2

-

0.5 NmP2

These simple ratios can be used in the program of lEI. To describe the shape of profile by a single analytic function of height, one needs also knowing the value of the derivative, dN/dh, at the inflexion point (3,4,5]. The latter can be derived in a first approximation from continuity of the slope under assumption of a piecewice-parabolic fitting of the 11(h) profile [13]: (dN/d]1)g

= 2

(Nm

-

Ng)/(hm

-

hg)

194

T.L. Gulyaeva

CONCLUSION When comparing the model electron density profile of IRI with the N(h) profile from the VI ionograms, a correction of shape of the IRI profile has been proposed by using the inflexion point below the peak of the F2layer. These parameters are estimated by simple relations from the main peak parameters of the ionosphere which are in turn the controlling input parameters In the IRI system. It should be noted, however, that the daily variability of the ionosphere as compared with the monthly averaged conditions suggests the need of updating the above parameters to be set up using the real-time VI observations. Working out this task appears to be practicable by combining the system of lEI with a system for N(h) analysis of the vertical—incidence ionograms. REFERENCES 1. 2.

3. 4. 5. 6. 7. 8. 9. 10. 11

•

12. 13.

K. Rawer, S. Raznakrisbnan and D. Bilitza, International Reference Ionosphere, URSI—COSPAR, Brussels, 1978. International Reference Ionosphere lEI 7~, cd. by K. Rawer, J. W. Lincoln and R. 0. Con]a~ight, Report UAG-82, WDC-A for STP, Boulder, Colorado, USA, 1981, IL G. Booker, J. Atm. Terr. Thy-s. 619 (1977). K. Rawer, this volume. T. L. Gulyaeva, Geomagn. and Aeronomy 22, No.6, In press (1982). J. W. Wright and A. K. Paul, Toward Global Monitoring of the Iono-ET1 w288 453 m492 45 sphere in Real Time by a Modern lonosonde Network, ~0AA Special Report, Boulder, Colorado, USA, 1981. T. A. .Anufrieva, in: Solar—Terrestrial Predictions Proc. vol.4, Boulder, Colorado, USA, p. C—58, 1980. R. 0. Conkright, Catalog of Ionospheric Electron Density Profiles Characteristic of Sunspot Maximum and Min4mu~Conditions, NOA.A Technical Memorandum EDIS NGSDC—5, Boulder, Colorado, USA, 1980. A. R. Laird and. J. W. Wright, Radio Sei. 2, 1255 (1967). N. I. Dvinskikh, in: Research in Geomagn., Aeronomy and Solar Thy-s., No.33, Irkutsk, USSR, 1975, p.114. N. I. Dvinakikh, An Nmpirical Model of Height—Frequencies Characteris-ET1 w220 330 m513 tics of the quiet Ionosphere over USSR, Preprint No.10—81, SibIZMIR, Erkutek, USSR, 1981. T. L. Gulyaeva, Radio Soi. j~,135 (1981). T. L. Gulyaeva, Geomagn. and Aeronomy jj, 741 ‚(1974). —

~‚