HAO 2012 Profiles In Science: Dr. Alan Burns

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Dr. Alan Burns received his graduate degree from the University of Canterbury in Christchurch, New Zealand. His thesis involved middle atmosphere studies. He came to NCAR/HAO in 2000. Dr. Burns does research into the physics of the thermosphere and ionosphere with particular emphasis on neutral composition and geomagnetic storm effects. Current efforts are centered on CISM verification and development, producing a new capability to image the thermosphere in FUV (GOLD mission) and developing science from the COSMIC data.

Publications

High Resolution

(1) Burns A.G., S.C. Solomon, W. Wang, L. Qian, Y. Zhang, and L.J. Paxton. 2012: Daytime Climatology of Ionospheric N_mF_2 and h_mF_2 from COSMIC data, J. Geophys. Res., in press.

Abstract: Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) data were analyzed to study the climatological variations of the F_2 region ionosphere. A 30 day running median was applied to the daily medians of each geomagnetic latitude bin (10°) to remove the short term variability of the data. This permitted a better description of the long term daytime climatology across the most recent solar minimum to be obtained. Several significant features appeared in this climatology: 1) low-latitude N_mF_2 was dominated by the semi-annual anomaly, the equatorial anomaly and the annual asymmetry (anomaly); 2) Semi-annual and annual anomalies extended into the middle latitudes; 3) this extension into the middle latitudes appears to be dependent on variations of solar radiation over the solar cycle, as the variations did not reach as far poleward in 2008 as they did in 2010; 4) The second equinoctial maximum is not centered on the September equinox, but occurred in October; 5) there is an annual variation at high latitudes in which maximum values of N_mF_2 occur in summer—there is no indication of a winter anomaly and, in fact, when hemispheres are compared, maximum N_mF_2 at mid latitudes always occurs in the summer hemisphere rather than the winter one; 6) the highest values of h_mF_2 at low latitudes occur on the summer side of the magnetic equator throughout the four year period, probably resulting from winds blowing from the summer to the winter; 7) minimum values of h_mF_2 at middle latitudes occur in winter, when h_mF_2 is typically 30 to 50 km lower than it is in summer; 8) elevated h_mF_2 also occurs in summer at high latitudes, with a distinct seasonal and hemispheric asymmetry.

Figure caption: N_mF_2 climatology for 2007 to 2010 in magnetic latitude bins. Units are in per cubic centimeters. Each bin is calculated using the median of data from all longitudes for local times between 0900 and 1500 local solar time. The data were then further processed by taking a 30 day running median for each bin to remove short term variability like geomagnetic activity and any possible short term “breathing” modes of the atmosphere.

High Resolution

(2) Burns, A. G., W. Wang, S. C. Solomon and L. Qian. 2012: Energetics and Composition in the Thermosphere, Geophysical Monographs.

Abstract: The thermosphere is defined by the high temperatures that occur in its upper regions. These high temperatures result from the absorption of energetic EUV radiation combined with weak in situ cooling. Heat is eventually lost from the upper thermosphere primarily through downward heat conduction. This heating and cooling is modified through a variety of processes, the most important of which at low and middle latitudes is heating by compression and cooling by expansion. These thermal processes help to drive the dynamics of the thermosphere, which, in turn, are a major cause of changes in neutral composition. In this paper we discuss the global changes in heating that arise as a result of high latitude energy inputs during geomagnetic storms, and the ways that we can gain a better understanding of these processes. One of the scientific results of this paper was that low and middle altitude heating during a simulated geomagnetic storm was mainly caused by the propagation and dissipation of gravity waves generated near the auroral zone.

Figure caption: Temperatures and winds at midnight plotted as a function of pressure surface and latitude for 4 UTs, from 0400–1000 at midnight local time during the main phase of the storm. Pressure level 0 corresponds to about 280 km at quiet time.

High resolution

(3) Thayer, J. P., X. Liu , J. Lei, M. Pilinski, and A. G. Burns. 2012: The Impact of Helium on the Thermosphere Mass Density Response to Geomagnetic Activity During the Recent Solar Minimum, J. Geophys. Res., 117, A7, doi:10.1029/2012JA017832.

Abstract: High-resolution mass density observations inferred from accelerometer measurements on the CHAMP and GRACE satellites are employed to investigate the thermosphere mass density response with latitude and altitude to geomagnetic activity during the recent solar minimum. Coplanar orbital periods in February 2007 and December 2008 revealed the altitude and latitude response in thermosphere mass density for their respective winter hemispheres was influenced by the relative amount of helium and oxygen present. The CHAMP-to-GRACE (C/G) mass density ratio depends on two terms; the first proportional to the ratio of the mean molecular weight to temperature and the second proportional to the vertical gradient of the logarithmic mean molecular weight. For the relative levels of helium and oxygen in February 2007, the winter hemisphere C/G mass density response to geomagnetic activity, although similar to the summer hemisphere, was caused predominantly by changes in the vertical gradient of the logarithmic mean molecular weight. In December 2008, the significant presence of helium caused the mean molecular weight changes to exceed temperature changes in the winter hemisphere leading to an increase in the C/G ratio with increasing geomagnetic activity, in opposition to the decrease observed in the summer hemisphere that was caused primarily by temperature changes. The observed behavior is indicative of composition effects influencing the mass density response and the dynamic action of the oxygen to helium transition region in both latitude and altitude will lead to complex behaviors in the mass density at GRACE altitudes throughout the extended solar minimum from 2007 to 2010.

Figure caption: a) Latitude-time plot of the natural logarithm of the GRACE and CHAMP mass density ratio normalized by the satellite altitude difference for a 30 day period starting from December 1, 2008 for 8 LT, b) Kp and F_10.7 indices and c) time series of the data in (a) at the specific latitudes of 58°S and 59°N.

Other References:

Qian, L., A. G. Burns, P. C. Chamberlin, and S. C. Solomon, 2012: Variability of thermosphere and ionosphere responses to solar flares, J. Geophys. Res., 10.1029/2011JA016777.

Wang, W., J. Lei, A. G. Burns, L. Y. Qian, S. C. Solomon, M. Wiltberger, J. Y. Xu, 2012: Ionospheric variability around the whole heliospheric interval in 2008, Solar Phys., 274, doi:10.1007/s11207-011-9747-0.

Luan, X., W. Wang, A. Burns, S. Solomon, Y. Zhang, L. J. Paxton, and J. Xu, 2012: Longitudinal variations of nighttime electron auroral precipitation in both the Northern and Southern hemispheres from the TIMED global ultraviolet imager, J. Geophys. Res., 116, A03302, doi:10.1029/2010JA016051.

Qian, L., A. G. Burns, S. C. Solomon, and P. C. Chamberlin, 2012: Solar flare impacts on ionospheric electrodynamics, Geophys. Res. Lett., 39, doi:10.1029/2012GL051102.

Lei, J., A. G. Burns, J. P. Thayer, W. B. Wang, M. G. Mlynczak, L. A. Hunt, X. K. Dou, and E. Sutton, Overcooling in the upper thermosphere during the recovery phase of the 2003 October storms, J. Geophys. Res., 117, doi:10.1029/2011JA016994.

Burns, A. G., S. C. Solomon, L. Qian, W. Wang, B. A. Emery, M. Wiltberger, and D. R. Weimer, 2012: The Effects of Corotating Interaction Region / High Speed Stream Storms on the Thermosphere and Ionosphere During the Last Solar Minimum, J. Atmos. Sol.-Terr. Phys., doi:10.1016/j.jastp.2012.02.006.

Wang, W., E. R. Talaat, A. G. Burns, B. A. Emery, S.-Y. Hsieh, J. Lei, A. D. Richmond, and J. Xu, 2012: The effect of subauroral polarization streams (SAPS) on global thermosphere and ionosphere: Model simulations, J. Geophys. Res., 117, A7, doi:10.1029/2012JA017656.

Solomon, S. C., A. G. Burns, B. A. Emery, M. G. Mlynczak, L. Qian, W. Wang, D. R. Weimer, and M. Wiltberger, 2012: Modeling Studies of the Impact of High-1 Speed Streams and Co-Rotating Interaction Regions on the Thermosphere-Ionosphere, J. Geophys. Res., 117, doi:10.1029/2011JA017417.

Qian, L., A. G. Burns, B. A. Emery, B. Foster, G. Lu, A. Maute, A. D. Richmond, R. G. Roble, Stanley C. Solomon, and W. Wang, 2012: The NCAR TIE-GCM: A Community Model of the Coupled Thermosphere/Ionosphere System, in press, AGU Geophysical Monographs.

Chen, G. M., J. Xu, W. Wang, J. Lei, and A. G. Burns, 2012: A comparison of the effects of CIR- and CME-induced geomagnetic activity on thermospheric densities and spacecraft orbits: Case studies, J. Geophys. Res., 117, A8, doi:10.1029/2012JA017782.

Yue, X., W. Schreiner , Y.-H. Kuo , D. Hunt , W. Wang , S. C. Solomon , A. G. Burns , D. Bilitza , J. Y. Liu , W. Wan , J. Wickert, 2012: Global 3-D Ionospheric Electron Density Reanalysis based on Multi-Source Data Assimilation, J. Geophys. Res., 117, A9, doi:10.1029/2012JA017968.