Solar particle events (SPEs) have been investigated since the late 1960's for possible effects on the middle atmosphere. Solar protons from SPEs produce ionizations, dissociations, dissociative ionizations, and excitations in the middle atmosphere. The production of HO(x) and NO(x) and their subsequent effects on ozone can also be computed using energy deposition and photochemical models. The effects of SPE-produced HO(x) species on the odd nitrogen abundance of the middle atmosphere as well as the SPE-produced long term effects on ozone. Model computations indicate fairly good agreement with ozone data for the SPE-induced ozone depletion caused by NO(y) species connected with the August 1972 SPE. The model computations indicate that NO(y) will not be substantially changed over a solar cycle by SPEs. The changes are mainly at high latitudes and are on time scales of several months, after which the NO(y) drifts back to its ambient levels

Douglass, Anne R.

Jackman, Charles H.

Meade, Paul E.

English

NASA Technical Reports Server

N90-28189
THE EFFECTS OF SOLAR PARTICLE EVENTS ON THE MIDDLE ATMOSPHERE
Charles H. Jackman and Anne R. Douglass I
Laboratory for Atmospheres
Code 616
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
U. S. A.
Paul E. Meade
Department of Astrophysical, Planetary, and Atmospheric Sciences
University of Colorado
Boulder, CO 80309
U. S. A.
INTRODUCTION
Solar particle events (SPEs) have been investigated since the late 1960's
for possible effects on the middle atmosphere. Solar protons from SPEs produce
ionizations, dissociations, dissociative ionizations, and excitations in the
middle atmosphere. Either directly or through a photochemical sequence both HO x
(H, OH, HO z) and NO x (N, NO, NO z) are produced as well. These HO x and NO x
constituents are important because they can lead to the destruction of ozone.
Most of these investigations have been primarily focused on the effects of SPEs
on ozone, however, a few have been related to the effects of SPEs on odd nitrogen
(N, NO, NO2, NO 3, N205, HNOz, HO2NO z, and CIONO 2) constituents.
The SPEs are good tests for model validation because the large
perturbations to the atmosphere associated with SPEs are confined to high
latitudes, last only for days to months, and are easily distinguished in
satellite data. This allows the comparison of measurements with a wide variety
of models, ranging from simple point models to two-dimensional models.
Ozone depletions have been observed during and after nine separate SPEs
over the past two solar cycles (HEATH et al. 1977; MCPETERS et al. 1981; THOMAS
et al. 1983; SOLOMON et al. 1983; MCPETERS and JACKMAN, 1985). SPEs have also
been observed to increase NO during one SPE (MCPETERS, 1986).
The production of HO x and NO x and their subsequent effects on ozone can
also be computed using energy deposition and photochemical models. We discuss
the effects of SPE-produced NO x species on the odd nitrogen (NOy) abundance of
the middle atmosphere as well as the SPE-produced long-term effects on ozone.
The influence of HO x species on ozone has been discussed in other papers (e.g.,
SOLOMON et al. 1981; JACKMAN and MCPETERS, 1985) and will not be repeated here.
ODD NITROGEN (NOy) VARIANCE DUE TO SPEs
The production of NOy species by SPEs has been predicted since the mid
1970's (CRUTZEN et al. 1975). Recently, a satellite measurement (MCPETERS,
1986) was made of the NO increase after a major SPE (July 1982). This measured
NO increase was in good agreement with our predicted NO increase, computed
tUnlverslties Space Research Association Resident Associate
https://ntrs.nasa.gov/search.jsp?R=19900018873 2020-03-19T21:13:27+00:00Z
130
assuming1.25nitrogen (N) atomsproducedper ion pair (PORTERet al. 1976).
The agreementbetweenthe predicted and measuredNOincrease has given us
confidencein the reliability of the computationsfor NOyspecies' increase
causedby SPEs.
A datasetof proton fluxes hasbecomeavailable fromThomasArmstrongand
colleagues(University of Kansas)whichallows for a daily computationof ion
pair productionand,subsequently,NOyproductiondueto SPEs.Theprotonfluxes
aregivenin integral formfor energiesgreater thanI0 MeV,30MeV,and60MeV.
Thedataare available for the timeperiod 1963through1985. Wehaveusedthose
data in a mannersimilar to that discussedin JACKMANand MEADE(1988) and
computea daily ion pair production over the 23 year time period in a form
suitable for inclusion in our model.
Theion pair productioncomputedwith the useof the daily averageproton
flux data of T. Armstrongcomparesfavorably with the ion pair production
computedusing thehourly averageprotonflux datafoundin the SolarGeophysical
Datapublication for mostSPEs.Howeverfor the August1972SPE,the ratio of
thehourly computedion pair productionto thedaily computedion pair production
rangesfromabout3.7 in the stratosphereto near1.0 in themesosphere.Wehave
normalizedthe daily to thehourly computedion pair productionfor this oneSPE
only for tworeasons:I) the hourly computedion pair productionis believed to
bemoreaccuratethan the daily computedion pair productionand2) the August
1972SPEis the mostimportantSPEin the last twosolar cycles for its effects
on the middleatmosphere.
Theion pair productionwasinput into our two-dlmenslonalphotochemical
model(DOUGLASSet al. 1989)whosevertical rangehasbeenextendedto be from
the groundto about90kmwith abouta 2 kmgrid spacingandfrom -85°Sto 85°N
with a i0 ° grid spacing. It was assumed that 1.25 N atoms are produced per ion
pair in this model computation. The SPE production of N atoms was only input
at geomagnetic latitudes above 60 ° (see JACKMAN and MEADE, 1988, for an
explanation).
The two-dimensional model was run to an annual equilibrium condition in
which the seasonal values of constituents repeat yearly. The model was then run
for 23 years from 1963 through 1985 and investigated for changes. For all model
runs in this investigation the ultraviolet flux was not allowed to vary with the
solar cycle.
Figure la illustrates the variability of NOy at 1.7 mb (44 km) and 75°N
over the 23 year period. Note that NOy can vary dramatically after an SPE,
especially after the August 1972 SPE, but the NOy values generally return to
their ambient levels 2 to 6 months after the event. The NOy seems to be affected
only by those SPEs which have an ion pair production over about i00 ion pairs
(cm -3 sec-1). This is not a strict rule as the time of year and, therefore, the
ambient NOy amount help determine the magnitude of the NOy change at a certain
level (see JACKMAN and MEADE 1988 for further discussion). Some downflux of NOy
from the SPE's mesospherlc production of NOy is also associated with the SPEs and
is important during certain seasons (late fall, winter, and early spring). This
downflux can also influence the amount of NOy in the upper stratosphere.
Figure la, as well as our analysis of NOy at other altitudes and latitudes,
indicate that the NOy produced by SPEs over solar cycle time periods does not
build up, but can be important at high latitudes on seasonal time-scales. This
result is not surprlzlng given the small fraction of the annual odd nitrogen
budget that was computed by JACKMAN et al. (1980) to result from SPEs. The
majority of the annual production of odd nitrogen is a result of nitrous oxide
oxidation and was recently computed (JACKMAN et al. 1987) to be 2.7 X 1034 NO
molecules per year. The largest production of NO molecules from SPEs was in the
131
year 1972 at the level of 6.4 X 1033 NO molecules per year, only 24_ of the
nitrous oxide source. The production of NO molecules from SPEs in other major
SPE-active years is typically half or less than that computed for 1972.
LONG-TERM OZONE VARIANCE DUE TO SPEs
Figure Ib illustrates the variability of ozone at 1.7 mb (44 km) and 75°N
over the 23 year period. The ozone decreases are directly correlated with the
NOy increases presented in Figure la.
The percentage change in modeled ozone as a result of the August 1972 SPE
is given in Figure 2 at two latitudes. The latitudes in the Northern Hemisphere
(N.H) at 75°N (Figure 2a) and 55°N (Figure 2b) indicate a larger ozone depletion
at 75°N than at 55°N. Other latitudes investigated from our model results show
a similar behavior with the larger ozone depletions being associated with the
higher latitudes. This behavior was also observed in the BUV ozone data (JACKMAN
and MCPETERS, 1987). The magnitude of the depletion observed in the BUV dataset
was similar to that predicted by the model computation. For example, about a
15-25_ maximum ozone depletion was observed between 70 ° and 80°N and about a 5-
15_ maximum ozone depletion was observed between 50 ° and 60°N.
Our model results at 55°S (not shown) indicates over a 20_ ozone depletion,
but the model at 55°N indicates a 5-i0_ depletion in the time period 20 to 60
days after the SPE, implying a large hemispheric difference in the level of ozone
depletion. MAEDA and HEATH (1980/81) showed that the S.H. did experience a
larger ozone loss than did the N.H. SPE-produced NOy in winter has a far greater
effect on ambient NOy amounts and, therefore, on ozone levels than does SPE-
produced NOy in summer (see JACKMAN and MEADE, 1988, for more discussion on SPE
effects on NOy amounts).
DISCUSSION AND CONCLUSIONS
Model computations indicate fairly good agreement with ozone data for the
SPE-induced ozone depletion caused by NOy species connected with the August 1972
SPE. Future studies should include a more detailed intercomparison of the ozone
behavior with altitude, latitude, and time. It would also be useful to compare
these detailed studies with another large SPE, perhaps one that occurs during
the current solar active period. Since NOy constituents are responsible for over
70_ of the ozone loss in the stratosphere (JACKMAN et al. 1986), it is useful
to validate the NOy photochemistry which is used in atmospheric models to predict
ozone amounts.
Our model computations indicate that NOywill not be substantially changed
over a solar cycle by SPEs. The changes are mainly at high latitudes and are
on time scales of several months, after which the NOy drifts back to its ambient
levels.
ACKNOWLEDGEMENTS
The authors would llke to thank Thomas R. Armstrong (University of Kansas)
for sending solar proton data that was used in the ion pair production
computations for this paper. We would also like to acknowledge Sushil Chandra
of NASA Coddard Space Flight Center for useful comments on an earlier version
of this manuscript.
132
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133
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The effects of solar particle events on the middle atmosphere

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