Software was prepared for removal of the external field due to the ring current and the associated induced part. Fast Fourier transformation was used to analyse the field of lithosphere with and without external current (+ induced internal current) component. A vertical component in the equatorial electrojet current system was identified from MAGSAT records

Rastogi, R. G.

English

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https://ntrs.nasa.gov/search.jsp?R=19830005255 2020-03-21T05:23:52+00:00Z
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PROGRESS REPORT
	
MAGSAT FOR GEOMAGNETIC STUDIES OVER nmim REGI
	
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Investigation Number M-38-
fi Author ' s name
	 Prof R G Rast
¢fir 	 Organisation
	 `Indian Institute of Geomagnetism
R•	 Colaba, Bombay 400 005, India
Type of Report	 Third Progress Report
Reporting Date
	 August 1, 1982
Investigation Period
	 April 1, 1982 to July 31, 1982
The investigation team consists of the following members:
R G Rastogi, B P Singh, D R K Rao,
G K Rangarajan, R Rajaram, M Roy
and B R Arora
during the investigation period:
The following collaborators participated in data analysis
S Srinivasan and L Carlo
I. Summary
The major activities of the period were: (i) to
prepare software for removal of the external field due to the
ring current and the associated induced part; (ii) td Fourier
analyse the field of lithosphere with and without external
current (+ induced internal current) component and (iii) the
studies of features of equatorial electrojet from MAGSAT records.
II. Techniques
Since the MAGSAT data has significant contributions
from the external field due to the ring -current and other
magnetospheric currents and their associated induced field,.a
correction for these must be made to isolate components of
i:&.CEIVED
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lithological origin only. To suppress other magnetospberic
currents one selects passes with low Kp values. Still correction
for ring currents has to be made. Though these have been
estimated and provided for by NASA, the values of E & I
were estimated using the total field. Since MAGSAT data
provides vector components, E & I could be estimated using
X and Z separately. This has been done in the present investi-
gation. The potential function used for the ring current
effects is of the conventional foam:
U	 CL 1-la t- t C Y )2TJ CCS 8
where e = 90- A. A being the dip latitude. Y is radial
distance to the data point and a is radius of Earth taken as
6371.2 km. E & I represent external and internal parts
respectively of t2'tt potential function. By using X and Z
tv estimate'E & I, the least squares problem incidentally remains
as a linear one.
Over the Indian region whore declination is very small
1°), the above correction'does not give any contribution to
the Y-field. The corrected X- and Z-fields were then subjected
to a fast Fourier transformation (FFT) and tt.e spectrum was
compared with similar spectrum obtained for the same pass before
correcting for the ring current effect. This was done to see
how the ring current modifies the spectrum to get a feeling of
the wavelengths which are affected most by the ring current
r
correction.
The study for the features of the equatorial electrojet
used the data from CHRONFIN tapes. The core field was removed
using sub-routine FDG sent by NASA. In this work ring current
contributions were removed using the E & I supplied by NASA.
1
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Two sets of morping and evening passes were analysed. The
passes in each set are such that they cross each other in the
neighbourhood of geomagnetic equator. This was done so
as to minimise the effects of crustal anomaly. The contribution
of equatorial electro jet was then estimated in e&O of the three
component X, Y & Z. These were subsequently used to investigate
the ionospheric current distributions.
III.	 Accomplishments
1) A program to compute E & I using X- and Z-components
have been developed and made functional.
2) Records from pass No. 46 & 47 for Indian region
were selected. E & I • estimates were made using the X- and Z-
values in the latitude region 30 6S to 30 •N. Spectrum of both
passes for both X and Z components were computed using PET.
3) A vertical component in equatorial electrojat
current system has been identified. This result is described
in more detail in the following section.
IV.	 Significant results
1) For pass Nos. 46 & 47, the estimated values of
I/E are 0.18 and 0.08 respectively. The corresponding values
as supplied by NASA are 0.10 and 0.01. A plot of X and Z
(only crustal + external) obtained for INVESTIGATOR-B i:ape
(after correcting for core fields) are given in Fig. 1. The
estimates of ring current effects are also given in the figure.`
The area covered is 10°S to 38 °N. It is noted that in both
the passes fit to Z-data is rather poor. This is partly
because the fact that the functional form of ring current
^1
4contribution is such that 8 must be sera at the dip equator.
2) X & Z (crustal + external) and X & Z (crust only)
for pass Nos. " & 47 were analysed through PIT. Data for pass
No. 47 is given in Fig. 2. The Fourier spectrum for the two
sets are given in Fig. 3. The spectrum was taken after removing
a linear trend and introducing cosine tapering. The data set
was extended to IM pts. In spectrum one not" that the smaller
wavelength components in both the passes are very little affectod
by the external current system; whereas for wavelengths around
(=2000 km) the spectral estimates are significantly different.
The effect is seen in both X and Z and also in both the passes.
These indicate that over the Indian region the contributions of
lithological features and wing currents are of same spatial
scales. This also explains why often a base level correction
is needed in different passes over the same region. Being of
same scale, the two causes will interfere with each other and
their isolation is natural to be a problem.
A higher amplitude for X crust or Z crust against the
value for X (crustal + external) or Z (crustal + external)
suggests that the two components have a opposing tendency.
3) The contributions from equatorial electrojet are
given in Fig. 4 for X, Y & Z components. The trajectories of
the passes analysed is given in Fig. S. The effect is distinctly
seen in X and Y components. In Z-component too its contribution
could be isolated. The results could not be accounted throuyli
a horizontal current component only in the equatorial electrojet.
Indications are that the vertical component extends up to and
beyond the NAC.a.T heights.
5
V. Publications : Nil
VI. Prob ems
	 : Nothing significant
VII. Data quality and deliver,
The delivery has been extremely fast and our requests
have been promptly attended.
VIII. Recommendations = Nothing for the preswit
IX. conclusions
Now that the necessary software for reducing the data
and separating the three components have been prepared, the
various analysis could be completed expeditiously.
s
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FiguKA Caotf na
Fig.l	 Plots of X (crust •+ external), Z (crust + external)
and Y (crust + extic al) for pass Non. 46 & 47.
External current component for X and Z are shown
by dotted lines. In the model adopted for external
currents contribution to Y is zero. Fig l(a) is
for pass No. 46 and 1(b) for pass No. 47.
Fig.2	 X and Z (crust + external) and X and 2 crust only
are shown for pass No. 47.
Fig.3	 Fourier spectrum for X (-H) and Z for pass Nos. 46 & 47.
Fig. 3(a) is for pass No. 46 and 3(b) for pass No. 47.
Continuous lines are for crust + external components
and solid lines for crustal component only. f
Fig.4	 Contributions from equatorial electrojet in X,Y and Z
components. In the upper plot X (solid) and Y (dotted)
are shown and the lower curve is for Z variations.
Fig.5	 Trajectories of passes analysed.
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MAGSAT for geomagnetic studies over Indian region

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