The correlations between the solar sectors and large-scale atmospheric vorticity in the lower atmosphere reported earlier are of interest since the solar-sector data appear to be independent of any terrestrial influences. It is shown that even these solar data may be affected by geomagnetic properties; a method for removing such influences is suggested

Deland, R. J.

English

NASA Technical Reports Server

N76 14545
Apparent Relationship Between Solar Sector
Boundaries and 300-Millibar Vorticity: Possible
Explanation in Terms of Upward Propagation
of Planetary-Scale Waves
RAYMOND J. DELAND
Polytechnic Institute of New York
It appears to be well established that large-
scale variations of pressure fields in the tropo-
sphere are propagated up to ionospheric levels,
to at least the E-region (Brown and Williams,
1971; Deland and Cavalieri, 1973). Correlations
between large-scale stratospheric variations and
ionospheric parameters are illustrated in figure 1,
taken from Deland and Cavalieri (1973). It seems
possible that the resulting changes in the iono-
sphere could cause variations in the magnetosphere,
and thus cause variations in geomagnetic parame-
ters such as the geomagnetic activity index Ap.
It therefore appears likely that at least some of
the observed correlations between geomagnetic
variations and meteorological variations may be
due to meteorological effects on the geomagnetic
variables, rather than due to a common solar
origin for the variations in both geomagnetic and
meteorological variations, as is commonly pre-
sumed. Partly because of these considerations,
the correlations between the solar sectors and
large-scale atmospheric vorticity in the lower
atmosphere reported by Roberts and Olson
(1973) and Wilcox et al. (1973) are of great
interest since the solar-sector data appear to be
independent of any terrestrial influences. It is
shown in this paper that even these solar data, as
analyzed by Wilcox et al. (1973), may be affected
by geomagnetic properties; and a method for
removing such influences is suggested.
WELL-DEFINED BOUNDARIES AND
THE BOW SHOCK
In their comparison of solar sectors and 300-
millibar vorticity, Wilcox et al. used the times of
passage of well-defined boundaries as key days in
a superposed-epoch analysis. The well-defined
boundaries were specified by Wilcox and Colburn
(1969) as those for which the magnetic polarity
was the same for at least 4 days before the bound-
ary and of the opposite sign for at least 4 days
after. According to Ness and Wilcox (1967), the
gaps in the data corresponding to the satellite
crossing the magnetosheath and magnetosphere
were partly compensated for as follows:
Whenever such a perigee gap has a given field polarity
both before the satellite entered the magnetosphere and
after the satellite returned to the interplanetary medium,
the gaps have been filled with that polarity.
Autocorrelations for the magnetic field polarity
obesrved by the satellite along its trajectory have
been published by Ness and Wilcox (1967) and
Wilcox and Colburn (1969). The autocorrelation
function falls off quite rapidly for 2 or 4 days'
lag, as of course it must in view of the tendency
of the polarity to be repeated after 7 to 10 days,
according to the characteristic sector structure
described by Wilcox, Ness, and their coworkers.
The observed autocorrelation at a given lag can
be considered to be an estimate of the quantity
163
https://ntrs.nasa.gov/search.jsp?R=19760007457 2020-03-22T18:21:07+00:00Z
164- RELATIONSHIPS BETWEEN SOLAR ACTIVITY AND METEOROLOGICAL PHENOMENA
JANS 1965
FIGURE 1.—Simultaneous variations of ionospheric and
•stratospheric variables over Aberystwyth from Janu-
ary 9 to March 11, 1965, taken from Deland and
Cavalieri (1973): Z« is the height of a constant elec-
tron density surface in the E-region (Brown and
Williams, 1971); /t represents smoothed variations of
/-min; Z» is the height of the 10-millibar surface over
Aberystwyth (Brown and Williams, 1971); and 'Ztn is
the smoothed variation of 10-millibar height corre-
sponding to the first three zonal wave numbers.
(2P — 1), where P is the probability of observing
the same polarity at a given time and at a time T
later. It follows that the probability of observing
a given polarity, assuming that the same polarity
was observed a few days previously, varies with
the time delay.
In figure 2 a schematic diagram of Earth's bow
shock and a satellite orbit such as that of IMP 3 is
shown. Because the figure is schematic, it is not
meant to be realistic. In the .figure, 2 and 3 denote
points just outside the bow shock that fall within
4 days after passing X. Let us assume that there
SUN.
FIGURE 2:—Schematic diagram of a satellite orbit and
the bow shock, showing the possibly well-defined
boundary of a magnetic sector at X. Point / is just
after the sector boundary, and points 2 and 3 are just
before' and just after, respectively, the satellite en-
counters the bow shock.
is a ('—,'+)'crossing at X; therefore, there is posi-'
live polarity at "1 and the previous 4 days were all
negative. The probability that the boundary cross-
ing at X will be recorded as well defined is then
the probability that positive. polarity is recorded
for the following 4 days. This will depend on the
probability of recording positive polarities at
points 2 and 3, conditional on positive polarity at
7, because the polarity at both must be positive
for a well-defined boundary to be recorded. These
probabilities in turn will depend on the position
of the bow shock because this will determine the
time lags between point / and points 2 and 3. For
instance, the wider the bow shock, the less likely
it is that the polarity at both points 2 and 3 will
be positive and thus enable continuity of polarity
across the gap to be recorded as specified by Ness
and Wilcox (1967). It follows that the probability
of a well-defined boundary being recorded will
depend to some extent on the width of the perigee
gap. This will be so for all the boundaries
recorded by the satellites with periods of 8 days
or less, and for a varying fraction of the bound-
aries for all other satellites. As a consequence,
the well-defined boundaries may include a higher
proportion of cases for which the bow shock and
magnetopause were relatively close to Earth, and
fewer' for a 'relatively disturbed "pushed out"
magnetosphere. If the latter occurs in part
SOLAR SECTOR BOUNDARIES AND 300-MILLIBAR VORTICITY 165
because of atmospheric influences, the possibility
of bias due to a positive correlation arising from
accidental selection of the data is apparent.
CONCLUSION AND RECOMMENDATIONS
The possibility that the correlations reported
by Roberts and Olson (1973) may be due to
accidental selection of the solar sector data is
sufficiently serious that further analysis should be
undertaken with special care to avoid the prob-
lems discussed in this paper. One method would
be to avoid all selection; that is, include all bound-
ary crossings in the analysis. This is difficult to
do because of the perigee gap: this approach
might easily lead to more boundary crossings with
a smaller gap than with a larger one. The only
way to be certain appears to be to use only those
boundary crossings for which the satellite was
some fixed distance, such as 20 Earth radii, ahead
of the Earth for 4 days before and 4 days after,
which would in§ure that the selection is not
affected by the bow shock or magnetosphere.
REFERENCES
Brown, G. M., and D. C. Williams, 1971, "Pressure
Variations in the Stratosphere and Ionosphere," /.
Atmos. Terr. Phys., 33, pp. 1321-1328.
Deland, R. J., and D. J. Cavalieri, 1973, "Planetary-
Scale Fluctuation of Pressure in the E-Layer, F-Min,
and Pressure in the Stratosphere," /. Atmos. Terr.
Phys., 35, pp. 125-132.
Ness, N. F., and J. M. Wilcox, 1967, "Interplanetary
Sector Structure, 1962-1966," Solar Phys., 2, pp. 351-
359.
Roberts, W. O., and R. H. Olson, 1973, "New Evidence
for Effects of Variable Solar Corpuscular Emission of
the Weather," Rev. Geophys. Space Phys., 11, pp.
731-740.
Wilcox, J. M., and D. S. Colburn, 1969, "Interplanetary
Sector Structure in the Rising Portion of the Sunspot
Cycle," J. Geophys. Res., 84, pp. 2388-2392.
Wilcox, J. M., P. H. Scherrer, L. Svalgaard, W. O. Rob-
erts, and R. H. Olson, 1973, "Solar Magnetic Struc-
ture; Influence of Stratospheric Circulation," Science,
180, pp. 185-186.
DISCUSSION
WILCOX: We thank Dr. Deland for his interest in
our work, but I do not believe that the remarks are
relevant to it. The sector pattern is well defined almost
all the time, being either two or four sectors per solar
rotation as seen on spacecraft going out to Venus, for
example, where one will have continuous observations
for several months. You simply see that within a given
sector you have the field completely in one direction,
except for filaments of a few hours' width, and then you
have a boundary, and then you have the next sector.
I just do not see the relevance of all this. I could
comment that the particular autocorrelation that you
chose for 1965 was the one interval of a few months
out of the 10 yr now observed in which the sector pat-
tern was less well defined than the others. There are a
number of other published autocorrelations, for example,
any of which you could have chosen that would have
had a considerably longer time to go down to zero. It
seems to me, however, that the basic point is just that
spacecraft observations away from Earth establish very
clearly that one has either a two- or a four-sector pat-
tern with a very sharp boundary.
If there is a suggestion of a selection effect, it would
seem that the clearest way to remove that possibility is
to have no selection at all. We worked with 54 bound-
aries that were well observed by spacecraft. The inter-
planetary field for 4 days on each side of the boundary
was unidirectional. For this particular interval, I sat
down and used the sector charts and counted the total
possible number of boundaries during this interval,
which came out to be 74. We, therefore', repeated the
analysis, using all 74 boundaries, in which case I do not
think there could be any selection effect. It seems to me
that if you have 54 out of 74 you are not dealing with
a problem of selection.
DELAND: Dr. Wilcox's point is well taken; however,
I am still concerned that, even with the 74 boundaries,
there is still some problem with the interpolation across
the perigee gap, but I have not had time yet to look into
this procedure. I still stick to my point, that if you really
want to be sure of having no problem, you should essen-
tially stay clear of Earth and any possible statistical
contamination.


Apparent relationship between solar sector boundaries and 300-millibar vorticity:  Possible explanation in terms of upward propagation of planetary-scale waves

Apparent relationship between solar sector boundaries and 300-millibar vorticity: Possible explanation in terms of upward propagation of planetary-scale waves

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server