NRL Presents Annual E.O. Hulburt Award for Scientific Achievement to Dr. Neil Sheeley

1/24/2005 - 1-05r
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Dr. Neil Sheeley of the Naval Research Laboratory's Space Science Division is the newest recipient of the annual E.O. Hulburt Award, the Laboratory's highest civilian honor for scientific achievement. Dr. Sheeley is head of the Solar-Terrestrial Theory Section in the Solar-Terrestrial Relationships Branch, where he is charged with formulating and carrying out a program on interdisciplinary studies of solar and interplanetary phenomena and their relationship to the terrestrial environment.

Dr. Sheeley is cited for over three decades of outstanding scientific contributions and for his enthusiastic leadership in the analysis and interpretation of observations from the SOLWIND and LASCO coronagraphs, which have maintained the Naval Research Laboratory as a world premier institution in solar coronal physics; for specific seminal contributions to our understanding of the solar magnetic field, the sunspot cycle, coronal holes, coronal mass ejections, and the solar wind.

Since joining NRL in 1973, Dr. Sheeley has used his unique combination of skills as both observer and theoretician to lead the scientific analysis effort on projects ranging from NRL's XUV spectroheliograph on Skylab to its white light coronagraph on the P78-1 and SOHO spacecraft. This work has led to an array of seminal discoveries.

Among Dr. Sheeley's accomplishments is the "NRL flux transport model," which has yielded major new insights into the evolution of the solar magnetic field and into the nature of the solar dynamo itself. In 1986, after winning one of the Laboratory's first Accelerated Research Initiatives (to study solar magnetic fields and their terrestrial effects), Dr. Sheeley assembled his own research group. Among the many successes of this group was the development in the 1990s of the Wang-Sheeley Model of the solar wind. This model correctly predicts the speed of the solar wind at the Earth and is now being used by NOAA to provide predictions of geomagnetic activity.

Dr. Sheeley and his collaborator, Dr. Yi-Ming Wang, have used the flux transport model to simulate the eleven-year cycle of the sun's magnetic field. Not only are they able to account for the major features of the cycle, but they can also account for its most puzzling characteristic, the reversal of the sun's magnetic field from cycle to cycle.

Dr. Sheeley attended the California Institute of Technology, both as an undergraduate and a graduate student. As part of his Ph.D. thesis, Dr. Sheeley measured the number of polar faculae appearing in Mount Wilson Observatory white-light plates from the year 1906 forward. The Sheeley polar facula counts are still used to this day because they provide the only quantitative measure of the Sun's polar fields before the advent of the magnetograph in the 1950s. In another part of his thesis work, Dr. Sheeley was the first to demonstrate that the magnetic fields on the Sun have strengths of many hundreds of gauss, not 10 gauss as believed at the time.

Dr. Sheeley later spent several years at Kitt Peak National Observatory, where he developed spectroheliographic techniques for observing magnetic fields and Doppler flows on the Sun, publishing his results in a classic series of papers. For example, his measurements of the solar-cycle variation of the calcium K-line emission provided the first indication that such measurements could be used to detect activity cycles in other stars, a result that has become a cornerstone of solar-stellar connection research and of research on solar ultraviolet variability. Dr. Sheeley has maintained a close association with Kitt Peak scientists throughout his career and has just completed a collaborative study of polarization effects in chromospheric emission lines with Dr. Christoph Keller.

In 1973, Dr. Sheeley was hired by Dr. Richard Tousey to work on the Skylab project. Over the next three decades, Dr. Sheeley led the scientific analysis of the data from the S082A XUV spectroheliograph on Skylab, from the SOLWIND coronagraph on P78-1 and from the LASCO coronagraph on SOHO. This work resulted in approximately 100 journal articles.

Dr. Sheeley's Skylab papers presented the first detailed study of XUV polar plumes, which may be important sources of heating in coronal holes and provided direct observational evidence for magnetic reconnection associated with the emergence of an active region into the corona. In another Skylab collaboration, he presented the first evidence that the long-duration X-ray emission from a post-flare loop system is always accompanied by a coronal mass ejection. Also, in collaboration with Dr. Leon Golub of the Harvard Smithsonian Center for Astrophysics, he showed that the brightnesses of individual coronal loops in small bipolar magnetic regions varied on timescales as short as six minutes, implying a nonsteady heating process. Other papers showed that the elemental abundances of newly formed coronal structures are systematically different from those of older structures.

The papers published by Dr. Sheeley and collaborators using NRL SOLWIND coronagraph observations have revolutionized our understanding of coronal mass ejections (CMEs) and their terrestrial effects. Included in these papers is the first report of an Earth-directed "halo CME," the type of solar ejection that causes the greatest terrestrial disturbances. Dr. Sheeley's work also established the relationship between CMEs and long-duration X-ray flares, demonstrated a nearly one-to-one correspondence between interplanetary shocks and fast CMEs, and established the relationship between CMEs and metric Type II radio bursts. Papers featured on the covers of Science and Nature magazines announced the serendipitous discovery of sungrazing (Kreutz) comets, which evaporated as they approached the Sun. This work was coauthored with NRL scientists, Drs. Donald Michels, Martin Koomen and Russell Howard.

Since the launch of SOHO in December 1995, Dr. Sheeley has played a leading role in the interpretation of data from the LASCO coronagraph. An important new result was the detection of "blobs" of coronal material that detach from coronal streamers and accelerate as they move outward. By tracking these inhomogeneities (now known as "Sheeley's blobs"), he was able to derive for the first time the velocity profile of the slow solar wind and pinpoint the location of the sonic point at about 5 solar radii from Sun center. In another major study, Dr. Sheeley showed that CMEs could be characterized by at least two different types of velocity profile: prominence-associated CMEs accelerate gradually, much like blobs, whereas flare-related CMEs begin at high speed and then decelerate. One of the most intriguing of LASCO discoveries has been the myriad of small inflows seen during the recent sunspot maximum.

Dr. Sheeley was able to show that these inflows occur preferentially at the boundaries of low-latitude coronal holes, indicating that they are signatures of the closing-down of interplanetary magnetic fields. He then produced the first major study of these inflows; the results were the subject of a NASA press release in November 2001.

During the 1970s, Dr. Sheeley became interested in coronal holes and high-speed wind streams, whose close association was firmly established by Skylab observations. In collaboration with Dr. Jack Harvey at Kitt Peak and Dr. William Feldman at the Los Alamos National Laboratory, he was able to demonstrate the rotation-by-rotation correspondence between coronal holes, high-speed streams, and geomagnetic activity over the solar cycle. In collaboration with Dr. Karen Harvey of Solar Physics Research Corp. and Dr. Jack Harvey, he also published important studies of the relationship between coronal holes and the photospheric magnetic field.

Dr. Sheeley has also made significant and widely recognized contributions to our physical understanding of the solar magnetic field. Together with Dr. C. Richard DeVore and Dr. Jay Boris of NRL's Laboratory for Computational Physics, he developed a procedure based on the NRL flux-corrected transport algorithm that allowed researchers to determine how this active region flux is dispersed over the solar surface through the combined action of supergranular diffusion, differential rotation, and meridional flow. The first papers utilizing the new code showed convincingly that the flux transport model could reproduce the observed behavior of both the mean and the gross field of the sun.

The most important result derived from the NRL flux transport model concerns the role of meridional flow. Dr. Sheeley and his collaborators have shown that the main agent is a 10-20 m/s poleward flow, which accounts for the large fluctuations in the polar fields observed around sunspot maximum. In addition, Drs. Wang and Sheeley found that the necessary existence of a 1 m/s equatorward "return flow" at the bottom of the solar convection zone accounts naturally for both 11-year period of the sunspot cycle and the well-known equatorward migration of sunspot activity. This new paradigm for the solar cycle has led to the recent development of "flux transport dynamos" to replace the traditional mean-field dynamo picture. Currently, Drs. Sheeley and Wang are collaborating with Dr. Judith Lean (NRL) to extend the model back to the 1645-1715 Maunder Minimum.

Dr. Sheeley received his B.S. and Ph.D. degrees in physics in 1960 and 1965, respectively, from the California Institute of Technology. Prior to joining NRL, Dr. Sheeley spent eight years at the Kitt Peak National Observatory in Arizona. He is a member of the American Astronomical Society (Solar Physics Division Treasurer, 1974-1977), the American Geophysical Union and the International Astronomical Union. Dr. Sheeley has also served on the Solar Physics Editorial Board, on NASA Peer Review committees, and as a member of the SOLIS Science Advisory Group.

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