HAO 2011 Profiles In Science: Joan Burkepile

Contact

303-494-1506
iquana@ucar.edu

Joan Burkepile is a Project Scientist III at the High Altitude Observatory (HAO), National Center for Atmospheric Research (NCAR). She received her degree in Physics from the University of Colorado, Boulder in 1983 and joined the High Altitude Observatory in July 1983. She studies Coronal Mass Ejections (CMEs), and the evolution of the solar corona. She is the Instrument Scientist for the Mk4 K-coronameter and the COSMO K-coronagraph.

Current Research

Changes in the total mass, brightness, and structure of the corona are due to changes in the energy deposited into the atmosphere by the Sun's magnetic field. Changes in the energy input into the lower solar atmosphere over the solar activity cycle, drive changes in the base density and temperature of the corona which in turn account for the variations in the structure, brightness and mass in the corona between activity minimum and maximum.

Figure 1 (left) caption: Plot of estimated mass in the low corona (1.2 to 2.2 solar radii) as a function of time over nearly 3-solar cycles as recorded by the Mauna Loa Mk3 and Mk4 K-coronameters. The coronal mass peaks during times of maximum solar activity (~1990, ~2000).

Figure 1 (right) caption: Two images of the solar corona recorded by the Mauna Loa K-coronameters; one at solar maxiumum activity in 2000 (left), and one at solar minimum activity (at right) in 2009.

Publications

(1) Burkepile, J.T., 2010: Science Requirements of the COSMO K-coronagraph, COSMO Tech Note #16.

Abstract: This technical note describes the scientific requirements of the K-coronagraph which is part of the Coronal Solar Magnetism Observatory (COSMO). COSMO is a proposed facility dedicated to studying coronal and chromospheric magnetic fields and their role in driving solar activity such as coronal mass ejections (CMEs). The major science goals to be met by the K-coronagraph are: 1)-To understand the formation of coronal mass ejections (CMEs) and their interaction with surrounding coronal structures and related activity (e.g. flares, prominence eruptions and shock waves); 2)-Identify Earth-directed CMEs (e.g. halos) in realtime; 3)-Determine the density distribution of the corona over solar cycle time scales; and 4)-Measure the radial brightness gradients beyond 1.5 R in magnetically open regions. The K-coronagraph instrument requirements derived from the science goals are shown in Table 1. The COSMO K-coronagraph will replace the aging Mauna Loa Solar Observatory (MLSO) K-coronameter which has been in operation since 1980.

(2) Thompson, W.T., K. Wei, J.T. Burkepile, J.M. Davila, O.C. St.Cyr, 2010: Background Subtraction for the SECCHI/COR1 Telescope Aboard STEREO, Solar Phys., 262, 213.

Abstract: COR1 is an internally occulted Lyot coronagraph, part of the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) instrument suite aboard the twin Solar Terrestrial Relations Observatory (STEREO) spacecraft. Because the front objective lens is subjected to a full solar flux, the images are dominated by instrumental scattered light which has to be removed to uncover the underlying K corona data. We describe a procedure for removing the instrumental background from COR1 images. F coronal emission is subtracted at the same time. The resulting images are compared with simultaneous data from the Mauna Loa Solar Observatory Mk4 coronagraph. We find that the background subtraction technique is successful in coronal streamers, while the baseline emission in coronal holes (i.e. between plumes) is suppressed. This is an expected behavior of the background subtraction technique. The COR1 radiometric calibration is found to be either 10–15% lower, or 5–10% higher than that of the Mk4, depending on what value is used for the Mk4 plate scale, while an earlier study found the COR1 radiometric response to be ~20% higher than that of the Large Angle Spectroscopic Coronagraph (LASCO) C2 telescope. Thus, the COR1 calibration is solidly within the range of other operating coronagraphs. The background levels in both COR1 telescopes have been quite steady in time, with the exception of a single contamination event on 30 January 2009. Barring too many additional events of this kind, there is every reason to believe that both COR1 telescopes will maintain usable levels of scattered light for the remainder of the STEREO mission.

Figure 2 caption: A Comparison of polarized brightness measurements made by the MLSO Mk4 (black) with those from COR1-A (red) and COR1-B (blue), as a function of position angle at various radial distances. Each scan is an average over 0.2 solar radii. The dashed lines represent fits to the COR1 data to best match the Mk4 values over most of the range. The fits have been smoothed for ease of reading. Sample error bars represent the radiometric uncertainty for each telescope.

(3) Frazin, Richard A., Alberto M. Vasquez, William T. Thompson, Philippe Lamy, Antoine Llebaria, Joan Burkepile, David Elmore, Russ Hewett, Farzad Kamalabadi, 2011: Intercomparison of the STEREO, SOHO and MLSO Coronagraphs and the POISE Eclipse Instrument. Submitted to Solar Phys.

Abstract: Shown are quantitative comparisons between polarized brightness (pB) and total brightness (B) images taken by the following white-light coronagraphs: COR1 and COR2 on STEREO, C2 on SOHO, and the ground-based MLSO-Mk4. Both the initial and final calibrations of C2 are discussed. The data for this comparison were taken on April 16 2007, when both STEREO spacecraft were still within 3.1° of Earth's heliographic longitude, affording essentially the same view of the Sun for all of the instruments. Generally, the agreement between the instruments is best in bright streamer structures due to the difficulties of estimating stray light backgrounds in COR1 and COR2 and the sky polarization in Mk4. The background subtraction is more effective for pB than it is for B in COR1, while the opposite is true for COR2.

Figure 3 (left) caption: The coronagraph images used for the intercomparisons are presented here. In each, the log of the pB value is displayed, and the inner and outer radii are shown in Table I. The COR1 and COR2 images are time-averages of 7 images and 3 images respectively, taken over a 60 minute span.

Figure 3 (right) caption: Plots of polarization brightness at 4 coronal heights from Mauna Loa Mk4 and STEREO COR1 A & B inner coronagraphs.

(4) McIntosh, Scott W., Joseph B. Gurman, Robert J. Leamon, Jean-Philippe Olive, Joan Burkepile, Robert S. Markel, Leonard Sitongia, 2011: The Hightest Cosmic Ray Fluxes Ever Recorded: What Happened to the Earth's Deflector Shield?
Submitted to Astrophys. J.

Abstract: The summer of 2009 saw the largest cosmic ray flux ever measured at 1 AU. Observed by neutron monitors, this solar minimum flux was 6% larger than that of the last solar minimum in 1996 and 4% larger than the previous high of the space age. Clearly, something dramatically affected the cosmic ray 'deflector shield' of the Earth this time around, but what was it? Using a combination of serendipitous observations made by the solid state recorder of the SOHO spacecraft, an analysis of SOHO/MDI magnetograms, combined with SOHO/EIT and SDO/AIA coronal imaging, we deduce that a pronounced north-south asymmetry in the meridional circulation flow resulted in the evolution of the photospheric magnetic field into a prolonged prevalence of negative magnetic polarity in the equatorial region that was the root cause of the observed cosmic ray flux increase. The regional dominance of the Sunward-pointing field, weakness and the low rigidity of the interplanetary magnetic field enabled more cosmic rays of the energy range measured at Earth to enter our atmosphere since systematic measurements began in the 1950s.