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Page 135
8—
Recommendations
Scientific Rationale For Assigning
Priorities
A program of investigation of solar energy inputs into all parts
of the Earth system is very much in concert with the goal and
objectives of the U.S. Global Change Program. The USGCRP is
motivated by the realization that global change can have tremendous
impact on conditions essential to life on earth. This realization
provides the basis for prioritization among the various components
that can be expected to comprise a USGCRP scientific element on
Solar Influences on Global Change. Of highest priority are those
activities that will be most important for national and
international policymaking.
Recommendations
Primary Recommendation
One activity ranks above all others for determining solar
influences on global change:
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OCR for page 135
Page 135
8—
Recommendations
Scientific Rationale For Assigning
Priorities
A program of investigation of solar energy inputs into all parts
of the Earth system is very much in concert with the goal and
objectives of the U.S. Global Change Program. The USGCRP is
motivated by the realization that global change can have tremendous
impact on conditions essential to life on earth. This realization
provides the basis for prioritization among the various components
that can be expected to comprise a USGCRP scientific element on
Solar Influences on Global Change. Of highest priority are those
activities that will be most important for national and
international policymaking.
Recommendations
Primary Recommendation
One activity ranks above all others for determining solar
influences on global change:
OCR for page 136
Page 136
1. Monitor the total and spectral solar irradiance from
an uninterrupted,overlapping series of spacecraft radiometers
employing in-flightsensitivity tracking.
There is an urgent need to rapidly implement the necessary long
term commitment for this monitoring because of the danger that the
present monitoring sequence will be interrupted and the long term
record invalidated as a result of lack of instrumental
cross-calibration. This primary recommendation is particularly
challenging and probably will not be achieved because of the dearth
of ready access to space.
A series of small spacecraft dedicated to solar monitoring could
provide the necessary data. Overlapping observations are required
to cross-calibrate measurements by different instruments whose
inaccuracies typically exceed the true solar variability.
Simultaneous observations from different instruments provide
important validation that real variability, rather than
instrumental degradation, is being measured and provide the
redundancy needed to preserve the long term data base in the case
of instrument failure. Improved radiometric long term precision and
calibration accuracies would contribute to a more reliable solar
forcing record.
In lieu of a spacecraft series dedicated to solar monitoring, it
may be possible to use the NOAA or DMSP operational satellites, for
which overlapping is a feature of their design.
Additional Recommendations
To augment the prime monitoring task, a suite of efforts from
diverse geophysical research fields is needed to achieve the USGCRP
objectives of monitoring, understanding, and predicting solar
influences on global change. Pursuit of recommendations 2 to 6 is
essential to the crossdisciplinary effort needed to reduce
uncertainties in knowledge of solar forcing of global change in
order to provide a sound scientific basis for policy-making on
global change issues. The actions of recommendations 7 to 12 are
essential to ensure that complete understanding is achieved of all
potential coupling mechanisms.
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2. Conduct exploratory modeling and observational studies to
understand climate sensitivity to solar forcing.
Implied connections between the Sun and the paleoclimate record
(Milankovitch orbital-induced variations and the Little Ice Age)
should be fully investigated for the insights they might provide
about the sensitivity of the climate system to solar forcing
compared with increased greenhouse gases. New knowledge should be
incorporated into existing GCMs utilized for climate
prediction.
3. Understand and characterize, through analysis of solar
images andsurrogates, the sources of solar spectral (and hence
total) irradiancevariability.
The overall goal of this activity is to improve the ability of
solar variability models to calculate solar radiative output
variations and to provide reliable proxies to bolster the
spaceborne monitoring effort. Toward this end, continue, without
interruption, to monitor from ground based observatories the
relevant proxy data, in particular certain relative spectral
irradiances (such as the He I and Ca II indices, and the 10.7 cm
flux) and solar images that display magnetic active regions (using,
for example, full disk magnetograms, and He I, Ca II, and white
light spectroheliograms). Use the improved solar variability models
to extend the variability record into the past and to predict
limits on future variability. Also important in this regard is
connecting the variability sources to the physical solar processes
that modulate the 14C and 10Be records.
4. Monitor, without interruption, the cycles exhibited by
Sun-likestars, and understand the implications of these
observations for long termsolar variability.
Tying the calculations of solar radiative output variations
derived from solar observations (Recommendation 3) to the broader
stellar context will help in this regard.
5. Monitor globally, over many solar cycles the middle
atmosphere'sstructure, dynamics, and composition, especially ozone
and temperature.
Long term records of ozone, temperature, and nitrogen oxides are
especially important as they may allow the separation of solar
from
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anthropogenic forcing in the troposphere. Solar effects on this
region will only be determined from the results of such
monitoring.
6. Understand the radiative, chemical, and dynamical
pathways thatcouple the middle atmosphere to the biosphere, as well
as the middleatmosphere processes that affect these pathways.
Both modeling and observational studies are needed.
7. Monitor continuously, with improved accuracy and long
termprecision, the ultraviolet radiation reaching the Earth's
surface.
This effort is critical, not only for determining the dosage of
UV radiation at Earth, but also because of the dependence of the UV
dosage on ozone concentrations, which are affected by both
anthropogenic and solar forcings.
8. Understand convection, turbulence, oscillations, and
magneticfield evolution in the solar atmosphere so as to develop
techniques forassessing solar activity levels in the past and
to predict them in thefuture.
A reliable theory of the solar activity cycle, of longer term
variability, and of stellar dynamos in general will require
physical descriptions of the processes that successfully reproduce
solar phenomena observed over a number of solar cycles. Reliable
monitoring of solar diameter could help to understand solar
variability processes. The goal is to understand why the Sun varies
at all.
9. Monitor continuously the energetic particle inputs to
theEarth's atmosphere.
Space based measurements should emphasize the higher
energies(> 100 MeV) and relativistic electrons.
Understand, through in situ measurements, the relationship of
space based measurements to the energy spectrum and fluxes of both
solar and galactic energetic particles reaching different altitudes
in the Earth's atmosphere.
10. Monitor the solar extreme ultraviolet spectral
irradiance (atwavelengths less than 120 nm) for sufficiently long
periods to fully assessthe long term variations.
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These measurements could be accommodated on the dedicated solar
monitoring spacecraft identified in Recommendation 1.
11. Monitor globally over long periods the basic
structure of thelower thermosphere and upper mesosphere so as to
properly define the presentstructure and its response to solar
forcing.
12. Conduct observational and modeling studies to
understand thechemical, dynamical, radiative and electrical
coupling of the upperatmosphere to the middle and lower
atmospheres.
Analysis of solar soft X-ray forcing of nitric oxide levels,
with possible inferences for nitrate deposits in ice cores, is an
example of such a study. Ultimately, a global model of the Earth
system is needed.
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Representative terms from entire chapter:
solar variability
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