SH21C-01 INVITED
The Whole Heliosphere Interval: Campaign Summaries and Early Results
The Whole Heliosphere Interval (WHI) is an internationally coordinated observing and modeling effort to
characterize the 3-dimensional interconnected solar-heliospheric-planetary system - a.k.a. the "heliophysical"
system. The heart of the WHI campaign is the study of the interconnected 3-D heliophysical domain, from
the interior of the Sun, to the Earth, outer planets, and into interstellar space. WHI observing campaigns
began with the 3-D solar structure from solar Carrington Rotation 2068, which ran from March 20 - April 16,
2008. Observations and models of the outer heliosphere and planetary impacts extend beyond those dates
as necessary; for example, the solar wind transit time to outer planets can take months.
WHI occurred during solar minimum, which optimizes our ability to characterize the 3-D heliosphere and trace
the structure to the outer limits of the heliosphere. Highlights include the 3-D reconstruction of the solar wind
and complex geospace response during this solar minimum, contrasts with the past solar minimum, and the
effect of transient activity on the "quiet" heliosphere.
Nearly 200 scientists are participated in WHI data and modeling efforts, ensuring that the WHI integrated
observations and models will give us a "new view" of the heliophysical system. A summary of some of the key
results from the WHI first workshop in August 2008 will be given.
http://ihy2007.org/WHI/
SH21C-02
Global MHD Modeling of the Solar Corona and Inner Heliosphere for the Whole Heliosphere Interval
Whole Heliosphere Interval (WHI), which runs from March 20 through April 16, 2008, and coincides with Carrington Rotation (CR) 2068 is providing a unique opportunity for both observers and modelers to collaborate in an effort to understand the three-dimensional structure and evolution of the solar corona and inner heliosphere. It builds on several previous "Whole Sun Month" intervals, which proved to be exceptionally successful. In support of WHI, we have developed a global MHD model solution for CR 2068. Our model, which includes energy transport processes, such as coronal heating, conduction of heat parallel to the magnetic field, radiative losses, and the effects of Alfven waves, is capable of producing significantly better estimates of the plasma temperature and density in the corona than have been possible in the past. With such a model, we can compute emission in extreme ultraviolet (EUV) and X-ray wavelengths, as well as scattering in polarized white light. Additionally, from our heliospheric solutions, we can deduce magnetic field and plasma parameters along specific spacecraft trajectories. In this presentation, we make detailed comparisons of both remote solar and in situ observations with the model results. Such comparisons allow us to: (1) Connect these disparate sets of observations; (2) Infer the global structure of the inner heliosphere; and (3) Provide support for (or against) assumptions in the MHD model, such as which physical processes are (or are not) important. The results of these simulations (including post-processing analysis and visualization tools) will be made available to the scientific community at http://predsci.com/WHI.
SH21C-03
First Results of 3D, Global EUV Tomography from the STEREO Mission: Solar Minimum Results
We present the first results of EUV tomography based on a month-long time series of 171, 195 and 284 Å images from the EUVI instrument on both STEREO A and B. The data were taken in April 2008 and correspond to CR2069. We show global, 3D maps of the emissivities in each band as well as the global, 3D differential emission measure. We show differences between active regions, cavity plasma (above chromospheric filaments), and "quiet Sun" plasma, and discuss implications for coronal heating. We use a statistically based data rejection procedure to remove the data corresponding to optically thick lines of sight before the tomographic algorithm is run.
SH21C-04 INVITED
The Extreme Ultraviolet Contributions to the Solar Irradiance Reference Spectrum (SIRS)
The Whole Heliosphere Interval (WHI) was a coordinated effort with inputs from over 50 models and
observatories, both satellite and ground based, to characterize the Sun and heliosphere during solar
minimum conditions. The time period selected for this quiet Sun WHI campaign was April 10-16, 2008. One
of the goals of the solar minimum WHI was to produce a definitive Solar Irradiance Reference Spectrum
(SIRS) for quiet Sun conditions ranging in wavelength from 0.1 nm up to 2400 nm. During this WHI campaign
on April 14, 2008, a sounding rocket was launched from White Sands Missile Range that observed the solar
spectral irradiance in these solar minimum conditions in the extreme ultraviolet (EUV) wavelength range from
0.1-106 nm as well as the bright hydrogen Lyman alpha emission at 121.6 nm. The rocket observations from
6.0-106.0 nm and at 0.1 nm spectral resolution are the EUV input for the SIRS. These rocket EUV
measurements are discussed following a brief introduction to the entire SIRS spectrum developed for the WHI
campaign.
http://ihy2007.org/WHI/DATA/Woods_Rocket/
SH21C-05 INVITED
Total solar irradiance during the last three cycles: What does the low present solar minimum tell us about long-term trends?
Since November 1978 a set of total solar irradiance (TSI) measurements from space is available, yielding a time series of 30 years. Presently, there are three TSI composites available, called PMOD, ACRIM and IRMB, which are all constructed from the same original data, but use different procedures to correct for long-term sensitivity changes. The PMOD composite is the only one which also corrects the early HF data for degradation. The results are not only important for solar radiometry from space, but they also provide a more reliable TSI during cycle 21. The comparison with a 3-component proxy model during this cycle allows also to expand it back to the minimum around 1975. Moreover, the PMOD composite uses VIRGO TSI data which cover the full cycle 23 with the same radiometers. This allows a direct comparison of the present minimum with the one in 1996 which can then be used to determine trends over a solar cycle. Comparison with the minima of the other two cycles allows some conclusions about the origin of long-term trends in TSI. The long- term variation of TSI must be due to another mechanism than the well established cycle variation, which is very similar to the variation of the spectral irradiance. This mechanism is most probably a global temperature change which is somewhat related to the amplitude of the cycle, that is to the total magnetic field.
SH21C-06
The Unusual Time History of Galactic and Anomalous Cosmic Rays at 1 AU over the Solar Minimum of Cycle 23
Studies of the galactic cosmic rays temporal variations (GCRs) over the "Modern Era" (from 1950s) establish the existence of a 22-year cosmic ray modulation cycle that is dominated by the 11-year solar activity cycle but is significantly influenced by gradient and curvature drifts in the interplanetary magnetic field (IPB) in association with changes in the tilt of the heliospheric neutral current sheet over the heliomagnetic cycle. In qA<0 epochs (when positive ions flow in along the neutral sheet and out over the solar poles), the solar minimum cosmic rays intensity is peaked over a period of several months (1965, 1987) in contrast to the 3 - 4 year plateau periods for qA>0 minima when the flow pattern is reversed. However, for 200 MeV/n GCR HE at 1 AU there is a quasi-plateau region for the cycle 23 solar minimum that now extends over some 12 months. The intensity level of this component is essentially the same as that of 1965 and 1987, as is the large depression of anomalous cosmic ray ACR He (10 - 40 MeV/n) relative to the qA>0 minima. There appears to be two different solar effects, the current sheet tilt in 2007 is less than in 1987 while the magnitude of the 1P B field is at its lowest value since essentially continuous measurements began in 1963. These will have off-setting effects on the GCR intensity. 10 Be and 14 C studies have shown that previous epochs of low solar activity [Oort (1050 AD); Spoerer (1420-1540); and Maunder (1615-1715)] have been marked by high cosmic ray intensity. There were other periods of reduced solar activity [Wolf (1320) and Dalton (1810)] which were associated with more moderate enhancements of the GCR intensity. Studies using data from the Cosmic Ray Network [IMP, ACE, neutron monitors at 1 AU, and Pioneer, Voyager, and Ulysses at greater heliocentric distances] are providing a better understanding of the solar phenomena that produce the cosmic ray modulation and should lead to an understanding of the solar changes in the distant past associated with the epochs of enhanced GCR intensity.
SH21C-07 INVITED
The Thermosphere at Solar Minimum: Geomagnetic, Atmospheric, and Anthropogenic Effects
Thermospheric temperature and density respond primarily to forcing by solar ultraviolet radiation, which causes dramatic changes on solar-cycle and solar-rotational time scales. However, the current extended period of low solar activity provides an opportunity for studying secondary effects that are less obvious when convolved with solar variability. Geomagnetic storms are less prevalent, but periodic forcing by co-rotating streams in the solar wind have been salient features during several recent years. Dynamical and compositional features propagated from the lower atmosphere, resulting particularly in systematic seasonal variability, are easier to analyze. Secular reduction in temperature and density due to increasing carbon dioxide and other anthropogenic greenhouse gases is both larger and more detectable during solar minimum. The confluence of these effects with a particularly long and deep solar minimum lead to a thermosphere that was likely colder and less dense during the summer of 2008 than at any other time during the past several centuries.