2008 Workshop:New Understanding of Thermospheric Density and Composition Structure and Variability
New Understanding of Thermospheric Density and Composition Structure and Variability
0800-1000 and 1030-1230 Saturday 21 June 2008
Format of the Workshop
two sessions of 2 hours each
Conflicts with other workshops
At least one of the two-hour sessions must be on the Saturday morning of June 21
Special technology requests
Brief Initial Description
New data on thermospheric density has become available from the CHAMP and GRACE satellites, while new studies of seasonal and long-term trends of satellite drag have advanced our understanding of these changes. Coordinated research programs involving several agencies are being conducted to further our knowledge of the causes of variability of thermospheric density and composition on a wide range of temporal and spatial scales, and to improve our ability to model and forecast this variability. The intent of this workshop is to gather the collective activities of these programs, present new results, and discuss plans for future studies.
This workshop seeks to increase collaboration among researchers studying thermosphere neutral density and composition structure and variability. New thermosphere data sets, such as CHAMP and GRACE, and funded research activities have generated a resurgence in studying the thermosphere on daily, seasonal and long-term time scales. The neutral properties of the thermosphere are the least known in our upper atmosphere and their mass, composition and motion impact the ionosphere strongly. This workshop solicits participation through presentations of new observations, new modeling studies, and new findings related to thermosphere density and composition structure and variability. It will also be of interest to have presentations indicting the impact of these thermosphere properties on the ionosphere.
There will be two sessions, each 2-hours in duration. The anticipated outcome of the workshop is to improve awareness and collaboration among participating research groups and to advance future plans and ideas on how to tackle the challenging problem of adequately describing the spatial and temporal response of the thermosphere to various forces and their impact on the geospace system.
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Post Workshop Summary
New thermosphere data sets, such as CHAMP and GRACE, and funded research activities have generated a resurgence in studying the thermosphere on daily, seasonal and long-term time scales. This workshop solicited participation through presentations of new observations, new modeling studies, and new findings related to thermosphere density and composition structure and variability. The workshop was well attended with over 40 participants and 16 presentations were given. Meeting minutes can be found on the CEDAR workshop wiki page.
The purpose of this workshop was to increase collaboration among researchers studying thermosphere neutral density and composition structure and variability. Art Richmond opened the workshop with a general discussion of thermosphere properties and provided the impetus for the workshop. John Emmert introduced long term trends in satellite drag data that indicated a decrease in thermosphere density of -2.68% / decade after removing solar cycle and annual cycle effects. Liying Qian presented seasonal variations in thermosphere density using NCAR – TIEGCM. To produce seasonal changes observed in O/N2 ratio by GUVI, the eddy diffusivity at the lower boundary of the TIEGCM needed to have a seasonal variation. A comment to this study was to see whether seasonal variations in geomagnetic forcing can produce the same effect.
Marcin Pilinksi (a CU graduate student) presented work on addressing the estimate of the satellite drag coefficient and the inherent difficulties in modeling the accommodation coefficient. Doug Drob introduced an updated NRL horizontal wind model with new data sets added and an improved algorithm. Kathrin Haeusler (a graduate student at the Geoforschungszentrum Potsdam) presented results from her colleague Stefanie Rentz concerning the CHAMP residual thermosphere density around the dayside cusp region. The anomalous cusp increase in density was about 30% for the 2002-2005 data set and is less distinct in the southern hemisphere. Tomoko Matsuo analyzed spatial patterns of CHAMP density variability using EOFs, finding that 99.2% of the density variability can be represented by the mean and the first four EOFs. Chin Lin presented latitudinal variations in neutral density and enhancements in thermosphere density observed above 70 degrees latitude during quiet times. These quiet time enhancements seem to occur around the morning to noon MLT regions. One comment was that such a localized feature will not be reacquired by CHAMP due to satellite precession and so one cannot tell how transient is the feature.
Geoff Crowley presented model results of EUV and Joule heating effects on thermosphere density. A four hour time lag is generally observed in the model after being forced by Joule heating. Cheryl Huang presented a new approach to empirically describing thermosphere density response by using the Dst index in the JB2006 model. The model seemed to have improved when compared with CHAMP data. Jiuhou Lei presented CHAMP density periodicities observed at 5, 7, 9, 13.5 and 27 days. He demonstrated that for periodicities less than 13.5 days there is no response by F10.7 and that very good correlations exist with periodicities observed in the solar wind high speed streams and Kp index. Art Richmond presented work performed by Yue Deng on electric field variability and the response of the thermosphere density. Model results indicate a 30-40% increase in thermosphere density when electric field variability is included.
Eric Sutton presented response times for CHAMP thermosphere density during geomagnetic storms. The high resolution data indicated that lag time varied with latitude and that as short as 1 hour response was observed in the high latitude summer with 2-3 hours at lower latitudes. Delores Knipp introduced Poynting flux measurements from DMSP 15 with interesting enhancements at the dayside cusp region. Aaron Ridley summarized a study of magnetic pole position and its effect on thermosphere density. Stronger density response was modeled when the pole is displaced towards night than towards day. Art Richmond addressed composition effects due to high latitude heating and the estimate of net upward molecular flux. The model assumed a time constant to Joule heating events of 10-100 minutes. Astrid Maute described model results when varying the spatial scale of the energy deposition, finding that narrower heating distributions with the same amount of energy as wider heating distributions produced substantially stronger response in thermosphere composition.
-Jeff Thayer and Art Richmond