SH23A-1617
Solar Wind 3D Reconstructions of the Whole Heliospheric Interval
3D tomographic reconstructions of the inner heliosphere have been used for over a decade to visualise and
investigate the structure of the solar wind and its various features such as transients and corotating
structures. Interplanetary scintillation (IPS) observations of the solar wind have been carried out for a much
longer period of time revealing information on the structure of the solar wind and the features within it. Here
we present such 3D reconstructions using IPS observations from the Solar Terrestrial Environment
Laboratory (STELab) and the Ootacamund (Ooty) Radio Telescope (ORT) of the Whole Heliospheric Interval
(WHI) Carrington Rotation 2068. This is part of the world-wide IPS community's International Heliosphysical
Year (IHY) collaboration. We show the structure of the inner heliosphere during this time and how our global
reconstructions compare with deep-space spacecraft measurements such as those taken by Wind, ACE,
STEREO, and Ulysses in terms of density and velocity.
http://ips.ucsd.edu/index_ss.html
SH23A-1618
Do in Situ Observations of Solar Wind Stream Interfaces Reflect the Evolution of Coronal Holes?
STEREO/PLASTIC observed at least four corotating interaction regions (CIRs) from March 2007 to April 2008. After observing a CIR stream interface at one observatory we estimated the time-of-arrival at the second STEREO observatory assuming radial propagation from a corotating source. In some instances the actual time-of-arrival did not agree with the prediction. This could be explained by changes in the solar wind speed at the source and/or by motion of the coronal hole from which the fast stream is emitted. We compare STEREO/PLASTIC observations of the stream interfaces with GONG coronal hole maps to see if the changes observed in situ are consistent with evolution at the source.
SH23A-1619
Unusual solar wind structure observed during the 2008 sunspot minimum
The solar wind during the sunspot minimum is known to have a stable bimodal structure, which is composed of a low-speed stream in a narrow latitude range around the equator and a high-speed stream over the poles. However, the solar wind structure determined from interplanetary scintillation (IPS) observations of the Solar-Terrestrial Environment Laboratory (STEL) for the current minimum period significantly differs from this typical feature. The STEL IPS observations indicate that the slow wind region extends to higher latitudes, while the fast wind exists over the poles. Furthermore, it is revealed from our IPS observations that another fast wind component is located near the equator, and the slow wind region split into northern and southern parts. This solar wind structure is consistent with a marked increase of the occurrence of fast winds at the Earth. Such an unusual feature may be attributed to the weak magnetic field intensity at the poles in the 2008 solar minimum. We consider that the evolution of the solar wind in the sunspot cycle 24 is likely to be significantly different from the previous ones.
SH23A-1620
STEREO ICMEs and their Solar Source Regions Near Solar Minimum
Although the quiet activity period surrounding the current solar minimum has prevailed since the launch of STEREO in October 2006, there have been at least 9 clear in-situ detections of ICMEs (Interplanetary Coronal Mass Ejections) by one or more spacecraft during the time the imagers were also operating. These observations provide unusually complete data sets for evaluating helio-longitude extent of the ICMEs and for identifying the probable solar cause(s) of the events. In this poster we present information on these ICMEs from the IMPACT and PLASTIC and ACE in-situ investigations, together with solar images from STEREO and SOHO that seem to capture the causative activity at the Sun. We find that even though the Sun was very quiet in '07-'08, with few active regions visible in GONG and SOHO magnetograms, there were numerous CME candidates that erupted through the near-equatorial helmet streamers. Most events could be identified with EUV disk activity as well as a coronagraph CME, even if the associated active region was very small or weak. Old cycle active regions, new and decayed, continued to maintain a warp in the large-scale helmet streamer belt that was a frequent site of the eruptions. However, the warp in the streamer belt may simply indicate that the active region(s) present is(are) sufficiently strong to affect the large scale quiet coronal field structure. Overall we see no gross differences between the solar activity and ICME causes during this and the previous solar activity minimum, when the Streamer belt was less warped due to the existence of stronger solar polar fields.
SH23A-1621
Drift Effects and Average Features of Cosmic Ray Density Gradient in Cirs During Successive Two Solar Minimum Periods
We deduce on hourly basis the spatial gradient of the cosmic ray density in three dimension from the directional anisotropy of high-energy (~ 50 GeV) galactic cosmic ray (GCR) intensity observed with a global network of muon detectors on the Earth's surface. By analyzing the average features of the gradient in the corotational interaction regions (CIRs) recorded in successive two solar activity minimum periods, we find that the observed latitudinal gradient (Gz) changes its sign from negative to positive on the Earth's HCS crossing from the northern to the southern hemisphere in A<0 epoch, while it changes from positive to negative in A>0 epoch. This is in accordance with the drift prediction. We also find a negative enhancement in Gx after the HCS crossing in both A<0 and A>0 epochs, but not in Gy. This asymmetrical feature of Gx and Gy indicates significant contributions from the parallel and perpendicular diffusions to the gradient in CIRs in addition to the contribution from the drift effect.
SH23A-1622
Dynamics of Quiet Solar Chromosphere at the Limb
We have observed the solar limb using 1024 × 1024 InSb Near Infrared Camera and Spectroheliograph at McMath-Pierce telescope during the solar minimum period of April 29 to May 1, 2008. A 120 micron slit, corresponding to 0.3 arc second was aligned perpendicular to the solar limb for the observations. The slit spectrum with a resolution of 0.036 Å corresponding to about 05 to 1.0 km/s were obtained in the wavelength regions of HeI 10830 Å, Hydogen Paschen α 12818 Å and Hydrogen Brackett γ 21661 Å. Excellent seeing conditions and the use of adaptive optics produced stable observing conditions during most of the observations. We present the results of line width variation as a function of chromospheric height around the solar limb.
SH23A-1623
RHESSI Observations of Facular Limb Darkening at 670 nm
We use observations from the solar aspect sensor of RHESSI to characterize the facular limb brightening function. The RHESSI observations, made with a rotating telescope in space, have great advantages in the rejection of systematic errors in the very precise photometry required for such an observation. The facular photometry is differential relative to a mean background limb-darkening function. The data base consists of about 1,000 images per day from linear CCDs with 1.73 arc sec square pixels, observing a narrow band at 670 nm. Each image shows a chord crossing the disk at a different location as the spacecraft rotates and precesses around its nominal solar pointing, with amplitude of a few arc sec. We reassemble these line images into synoptic images with a relatively low time cadence but an almost full coverage of more than six years. We further mask these images against SOHO/EIT 284A images in order to select magnetic regions. The resulting mean limb-darkening function is clearly resolved in radius and has a maximum at mu = 0.24 and approaches zero at the limb, consistent with Spruit's "hot wall" model. The contrast is positive at disk center, and we discuss explanations for this.
SH23A-1624
The Global Photospheric Temperature Field
We use observations from the solar aspect sensor of RHESSI to characterize the large-scale temperature variation across the solar disk. Previous observations have suggested the presence of a polar temperature excess as large as 1.5 K. The RHESSI observations, made with a rotating telescope in space, have great advantages in the rejection of systematic errors in the very precise photometry required for such an observation. This photometry is differential relative to a mean limb-darkening function. The data base consists of about 1,000 images per day from linear CCDs with 1.73 arc sec square pixels, observing a narrow band at 670 nm. Each image shows a chord crossing the disk at a different location as the spacecraft rotates and precesses around its nominal solar pointing. We reassemble these line images into synoptic images with a relatively low time cadence but an almost full coverage of more than six years. We further mask these images against SOHO/EIT 284A images in order to eliminate magnetic regions. The analysis establishes limits on the quadrupole dependence of brightness (temperature) on position angle, a crucial unknown in our precise measurement of the solar oblateness.
SH23A-1625
Solar Network Bolometric Properties at Minimum of Activity Observed by the Solar Bolometric Imager
On September 13 2007, the Solar Bolometric Imager (SBI) observed the Sun in wide band spectrally
integrated for 16 hours while suspended from a balloon at ~120,000 feet altitude above New Mexico. SBI
represents a totally new approach in finding the sources of the solar irradiance variation. Its detector is an
array of 320x240 thermal IR elements whose spectral sensitivity has been extended and flattened by a layer
of gold-black deposited on its IR sensitive surface. The combination of bolometric array and telescope, a 30-
cm Dall-Kirkham with uncoated primary and secondary Pyrex mirrors, provide an image of the Sun with
constant spectral response between ~ 280 and 2600 nm, over a field of view of 960 x 720 arcsec with a pixel
size of 3 arcsec.
The September 13, 2007 flight provided bolometric (integrated light) maps of the photosphere when the Sun
was near a minimum of activity. At the time of the flight no active regions were present giving us the
opportunity to measure with high accuracy the bolometric contrast of the weak solar magnetic network from
Sun center to the limb. The network was easily detectable by SBI near the limb. We measured an average
bolometric contrast of ~ 0.8 to 1.0 %, which is slightly above the 5-minute oscillation brightness signal (the
most prominent solar induced noise source for us). We were also able to detect the bolometric brightness
signature of network near Sun center by averaging 720 bolometric images taken close to Sun center over a
period of 1 hour. The resulting RMS noise was < 0.02% and most of the 5-minute oscillation brightness
was removed in the average. This enabled us to measure an average network bolometric contrast at Sun
center of 0.25% with a spread of about ± 0.05%. Ours is the first bolometric measurement (constant
spectral sensitivity from 280 to 2600 nm) of the center-to-limb contrast of magnetic network. Our
observations demonstrate that SBI can accurately measure the bolometric contrast of even quiet network
across the solar disk. These measurements will enable a more precise estimate of the TSI contribution from
changes of the enhanced magnetic network, which consist of larger elements than the quiet network. This will
enable us to determine whether other low level brightness sources besides faculae and spots contribute to
TSI and evaluate their possible long term influence in TSI change and climate.
http://sd-www.jhuapl.edu/SBI/
SH23A-1626
Photoelectrons Escaping the Ionosphere During the WHI: An Alternative Method to Validate the Temporal and Spectral Variation of the Solar Irradiance in the 1-50 nm Range.
We report observations of 10 eV to 1 keV photoelectrons produced by 1-50 nm solar irradiance during the Whole Heliosphere Interval (WHI). The observations were made from the FAST satellite at ~ 3,000 km. From March 20 to April 16, 2008 we found minimal (ie ~10%) variation in photoelectron flux at 25 eV, generated by EUV irradiance in the 27-31 nm range and large (i.e. >200%) variation in the photoelectron flux at 360 ev, generated by EUV irradiance in the 3 nm range. These variations are comparable to those found under more active solar conditions. We also compared the average photoelectron spectrum observed on April 14 with the solar irradiance observed from a rocket carrying a prototype of the SDO/EVE instrument on that day. The comparison was made using photoelectron fluxes calculated from the Field Line Interhemispheric Plasma (FLIP) code with the rocket spectrum as input. We found that the observed and calculated photoelectron spectra agree within 30% over all energies. This is a significant improvement from previous comparisons.
SH23A-1627
Solar Irradiance Reference Spectra (SIRS) for IHY2007 Whole Heliosphere Interval (WHI)
The IHY2007 Whole Heliosphere Interval (WHI) for solar Carrington Rotation 2068 (20 March to 16 April
2008) has been very successful in obtaining a wide variety of solar, heliospheric, and planetary observations
during times of solar cycle minimum conditions. One of these efforts is the generation of solar irradiance
reference spectra (SIRS) from 0.1 nm to 2400 nm using a combination of satellite and sounding rocket
observations. These reference spectra include daily satellite observations from TIMED Solar EUV
Experiment (SEE) from 0.1 nm to 116 nm and from Solar Radiation and Climate Experiment (SORCE)
instruments from 116 nm to 2400 nm. The EUV range is also improved with higher spectral resolution
observations from 6 nm to 105 nm using the prototype SDO EUV Variability Experiment (EVE) aboard a
sounding rocket launched on 14 April 2008. The SIRS result is an important accomplishment in that it is the
first time in having simultaneous measurements over the full spectral coverage up to 2400 nm and during
solar cycle minimum conditions. The SIRS data from 0.1 nm to 2400 nm and in 0.1-nm intervals (on 0.05 nm
centers) are available from http://ihy2007.org/WHI/.
http://ihy2007.org/WHI/
SH23A-1628
Changes in the Solar Minimum Irradiance in the Middle and Far Ultraviolet on Solar Cycle Timescales
The SOLar-STellar Irradiance Comparison Experiments (SOLSTICEs) on the Upper Atmosphere Research Satellite (UARS) and the Solar Radiation and Climate Experiment (SORCE) have been making daily measurements of the solar spectral irradiance (SSI) in the ultraviolet since 1991. This time period includes both the Whole Solar Month (WSM) in August 1996 with UARS observations and the Whole Heliosphere Interval (WHI) in April 2008 with SORCE measurements. Understanding instrument degradation and cross- calibrations between the two instruments is crucial for comparing these two data sets. Comparison between SORCE and UARS for the two quiet sun epochs indicates that the current solar cycle minimum is lower in the ultraviolet than the previous minimum observed by UARS. There is more confidence in this result for the far ultraviolet (120-200 nm) because the uncertainty in the instrument response is a smaller fraction of the solar variability than for the middle ultraviolet (200-300 nm).
SH23A-1629
13 Years of SOHO/CELIAS/SEM Calibrated Solar Extreme Ultraviolet Irradiance Data
A verified and updated version of the calibrated SOHO/CELIAS/SEM (absolute) solar extreme ultraviolet (EUV) measurements from the beginning of the mission in 1996 through the present is available at the University of Southern California Space Sciences Center website. To complete this new version, six (1999- 2006) sounding rocket under-flights were analyzed using measurements from both a very stable Rare Gas (Ne) Ionization Cell (RGIC) and a clone of the flight SEM instrument. These sounding rocket under-flights have provided a number of reference points that have been compared with the solar flux data published on our web site (last revised in 2000). These reference points are in good agreement with the solar cycle EUV flux for the 30.4 nm first order (26 nm to 34 nm) SEM channels, indicating a very small (less than 1 percent) averaged difference from the published flux for the six under-flights. Thirteen years of continuous and accurate SEM data will continue to provide important information about short term (solar flares) and long term (solar cycle) changes of EUV solar irradiance, and will be used for advancing solar models, for more accurate Earth atmosphere drag models, ionization proxies, and atmospheric dynamics generally, and will also provide solar EUV measurement overlap with the new SDO Extreme ultraviolet Variability Experiment (EVE), to be launched in 2009.
SH23A-1630
Solar Spectral Variability as measured by the SORCE SIM Instrument
The Spectral Irradiance Monitor (SIM) on-board the Solar Radiation and Climate Experiment (SORCE) satellite provides the first comprehensive measurements of solar spectral irradiance (SSI) variability from 200-2400 nm, accounting for about 97 percent of the total solar irradiance (TSI) incident at the top of the Earth's atmosphere. SIM observations indicate that, in addition to modulation due to active region passage, the SSI values for wavelengths with a brightness temperature greater than 5770 K show a brightening with decreasing solar activity, whereas below this value there is a dimming. These results demonstrate that different parts of the solar atmosphere contribute differently to the TSI with the behavior in the deep photospheric layers giving an opposing and nearly compensating solar cycle trend to that in the upper photospheric and lower chromospheric layers that produce the ultraviolet contributions. We will show these results over the last 4.5 years of the mission during the descending phase of Solar Cycle 23 that includes the solar minimum time period of the Whole Heliosphere Interval (WHI).
SH23A-1631
Modeling Tsi Variations Using Automated Pattern Recognition Software On Mount Wilson Data
This poster presents the results of using the AutoClass software, a Bayesian finite mixture model based pattern recognition program developed by Cheeseman and Stutz (1996), on Mount Wilson Solar Observatory (MWO) intensity and magnetogram images to identify spatially resolved areas on the solar surface associated with TSI emissions. Using indices based on the resolved patterns identified by AutoClass from MWO images, and a linear regression fit of those indices to satellite observations of TSI, we were able to model the satellite observations from the MWO data with a correlation of better than 0.96 for the period 1996 to 2007. The association of the spatial surface regional patterns identified by AutoClass with the indices developed from them also allows construction of spatially resolved images of the Sun as it would be "seen" by TSI measuring instruments like Virgo if they were able to capture resolved images. This approach holds out the possibility of creating an on-going, accurate, independent estimate of TSI variations from ground based observations which could be used to compare, and identify the sources of disagreement among, TSI observations from the various satellite instruments and to fill in gaps in the satellite record. Further, the spatial resolution of these "images" should assist in identifying with greater accuracy the particular solar surface regions associated with TSI variations. Also, since the particular set of MWO data on which this analysis is based is available on a daily basis back to at least 1985, and on an intermittent basis before then, it may be possible to construct an independent estimate of TSI emission at several solar minima to ascertain if there has been any significant increase or decrease, a topic of significance to determining what part, if any, solar TSI variations play in global warming. Cheeseman, P. & Stutz, J.,1996, in Advances in Knowledge Discovery and Data Mining, U.M. Fayyad, G. Piatetsky-Shapiro, P. Smyth, and R. Uthurusamny (Eds.). (AAAI Press), p.61
SH23A-1632
Constructing a Data System to Support Analysis of the Whole Heliosphere Interval
The Whole Heliosphere Interval is an internationally coordinated observing and modeling effort to
characterize the 3-dimensional interconnected solar-heliospheric-planetary system. The WHI observing
campaigns began with the 3-D solar structure from solar Carrington Rotation 2068, which ran from March 20
to April 16, 2008, and traced these structures through the heliosphere and into geospace. The WHI team has
developed a data and modeling clearinghouse to create a unified point of entry into the disparate data sets
spanning across the traditional disciplinary boundaries. Linkages are provided to data from the special
observing programs conducted by many observatories for the WHI effort, models that looked in detail at the
WHI and the many other data sets and models from the interval. We also explore the Virtual Observatory
landscape and highlight their contributions to the development of a more complete understanding of the
entire heliophysical system.
http://ihy2007.org/WHI/