HAO 2011 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

(1) Corotating Interaction Region / High Speed Stream Storm Effects on the Thermosphere and Ionosphere
Burns, A.G., S.C. Solomon, L. Qian, W. Wang, B.A. Emery, M. Wiltberger, and D.R. Weimer. 2011: The effects of corotating interaction region/high speed stream storms on the thermosphere and ionosphsere during the last solar minimum, J. Atmos. Solar-Terr. Phys., submitted.

Abstract: Geomagnetic storms at solar minimum are driven by the interaction between high speed streams and low speed streams (Corotating Interactions regions/High Speed Streams—CIR/HSSs), rather than by Coronal Mass Ejections (CMEs). Solar minimum storms are generally of smaller amplitude, but they also have other characteristics that affect the response of the thermosphere/ionosphere (TI) system to them. Burns et al. [2011] explore both the background upper atmosphere and the characteristics of these CIR/HSS events in 2008 using both models and data. Several features are apparent: 1) The nature of the CIR/HSS event was different in the second half of 2008 when the HSS were of short duration compared with the first half of that year when the onset of the next HSS overlapped with the declining phase of the previous one; 2) Individual HSSs had different impacts depending on the average sign of B_z and the duration of the event; 3) Equatorial N_mF₂ maximized at the equinox in both data and model; 4) No winter anomaly was apparent in the data, but one was present in the model runs; 5) Local time variations dominated the mean neutral densities; 6) NO cooling is maximum in the summer high latitudes; 7) CIR/HSS effects with extended recovery periods were very important if not dominant features of the plots of the first half of 2008; 8) Positive storm effects in N_mF₂ maximized on the day of the onset of the event at middle latitudes, whereas negative storm effects maximized on the next day at these latitudes; 9) Negative storm effects, neutral density increases and enhanced NO cooling continued for several days after the storm began, indicating the importance of continued forcing associated with Alfven waves and elevated solar wind speeds in the HSS.

(2) Overcooling in the upper thermosphere during storm recovery
Lei, J. A.G. Burns, J.P. Thayer, M.G. Mlynczak, L.A. Hunt, W. Wang, X. Dou, and E. Sutton. 2011: Overcooling in the upper thermosphere during the recovery phase of the 2003 October storms, J. Geophys. Res., submitted.

Abstract: Infrared radiative emissions by carbon dioxide (CO₂) and nitric oxide (NO) are the major cooling mechanisms of the lower thermosphere. During geomagnetically active periods, the NO density and cooling rate in the auroral regions increase significantly as a result of particle precipitation and Joule heating. Previous studies have shown that the time for NO density to recover to quiet time levels is longer than that of the thermosphere temperature or density recovery. Lei et al. [2011] explore the implications of these different recovery rates for the post-storm thermosphere. Thermosphere densities retrieved from the CHAMP and GRACE accelerometer measurements and NO cooling rates measured by TIMED/SABER are used to examine their variations during the post-storm period of the October 2003 geomagnetic storms. It was found that thermosphere densities at both CHAMP and GRACE altitudes recovered rapidly and continuously decreased below the quiet time densities during the post-storm period, especially at middle latitudes. Compared with the quiet time values, the maximum depletion in the CHAMP and GRACE densities after the storm is about 25–42%, and the estimated decrease of thermospheric temperature is as large as 70–110 K. Their analysis suggests that the elevated NO cooling rate, resulting from the slower recovery of NO densities in the post-storm period, is the cause for this overcooling of the thermosphere.

Ionosphere responses to an X6.2 flare occurred on September 9, 2005

Figure: High resolution

(3) Variability of thermosphere and ionosphere responses to solar flares
Qian, L., A. G. Burns, P. C. Chamberlin, and S. C. Solomon. 2011: Variability of thermosphere and ionosphere responses to solar flares, J. Geophys. Res., 116, A10309, doi:10.1029/2011JA016777.

Abstract: Qian et al. [2011] investigated how flare characteristics affect the thermosphere and ionosphere responses to them. Model simulations showed that, for flares with the same magnitude and location, the thermosphere and ionosphere responses changed significantly as a function of flare rise and decay rates. The "Neupert Effect", which predicts that a faster flare rise time leads to a larger EUV enhancement during the impulsive phase, caused a larger maximum ion production enhancement. In addition, model simulations showed that increased E×B plasma transport due to conductivity increases during the flares caused a significant equatorial anomaly feature in the electron density enhancement in the F region, but a relatively weaker equatorial anomaly feature in TEC enhancement, due to dominant contributions by photochemical production and loss processes. The latitude dependence of the thermosphere response correlated well with the solar zenith angle effect, whereas the latitude dependence of the ionosphere response was more complex, due to plasma transport and the winter anomaly.

Figure caption: Ionosphere responses to an X6.2 flare occurred on September 9, 2005. (a) NCAR TIME-GCM simulated enhancement of E×B at model pressure level lev=1.75. (b) the corresponding electron density enhancement at lev=1.75; (c) the corresponding TEC enhancement. 1 TECU is 10¹² electrons/cm²; (d) the corresponding enhancement of the sum of the ion production and loss at lev=1.75.