8:30am - 8:45am
Models and GOCE Measurements of Thermosphere Density and Wind Below 250 km
1Delft University of Technology, The Netherlands; 2British Antarctic Survey, UK; 3Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Germany; 4University of Michigan, USA
The last year of the science mission and the deorbit phase of GOCE offer a unique opportunity to assess the results of models of the density and wind in the middle and lower thermosphere. After depletion of GOCE's xenon fuel on the morning of October 21, 2013, when the satellite's mean geodetic altitude was 239 km, it took 3 weeks before the satellite disintegrated during re-entry, shortly after UTC midnight on November 11. A continuous record of instrument and housekeeping data was received until about 7 hours before re-entry, at which point the satellite's minimum geodetic altitude was just 138 km. Although the along-track axes of the accelerometers on GOCE were saturated two days before the re-entry, accurate acceleration data could still be derived from the continuous GPS tracking up to the final day. The result is that a unique set of partially redundant, but largely complementary data on the aerodynamic interaction of the atmosphere with the spacecraft is available for this sparsely sampled altitude range. Density and wind data derived for the GOCE deorbit phase, as well as the science data from the period of October 2012 to October 2013, have been compared with both empirical models (NRLMSISE-00, JB-2008, DTM-2013, HASDM, HWM07, HWM14) and general circulation models (WACCM-X, TIE-GCM, GITM, UAM-P), exposing the relative strengths and weaknesses of these models.
8:45am - 9:00am
Horizontal and Vertical Wind Measurements from GOCE Angular Accelerations
Delft University of Technology, Netherlands, The
Because of the highly accurate accelerometers, the GOCE mission has proven to be a unique source of thermosphere neutral density and cross-wind data. In the current methods, in which only the horizontal linear accelerations are used, the vertical winds cannot be obtained. In the algorithm proposed in this paper, angular accelerations derived from the individual gradiometer accelerations are used to obtain the vertical wind speeds as well. To do so, the measured angular rate and acceleration are combined to find a measurement of the torque acting on the spacecraft. This measurement is then corrected for modeled control torque applied by the magnetic torquers, aerodynamic torque, gravity gradient torque, solar radiation pressure torque, the torque caused by the misalignment of the thrust with respect to the center of gravity, and magnetic torque caused by the operation of several different subsystems of the spacecraft bus. Since the proper documentation of the magnetic properties of the payload were not available, a least squares estimate is made of one hard- and one soft-magnetic dipole pertaining to the payload, on an aerodynamically quiet day. The model for aerodynamic torque uses moment coefficients from Monte-Carlo Test Particle software ANGARA. Finally the neutral density, horizontal cross-wind, and vertical wind are obtained from an iterative process, in which the residual forces and torques are minimized. It is found that, like horizontal wind, the vertical wind responds strongly to geomagnetic storms. This response is observed over the whole latitude range, and shows seasonal variations.
9:00am - 9:15am
Spatio-temporal Variability of Thermospheric Density using ESA (Swarm mission) Data
1SERC Limited; 2SPACE Research Centre, RMIT University, Melbourne, Victoria, Australia
Monitoring and understanding the variability and driving mechanisms of atmospheric density in the thermosphere can lead to improved atmospheric density models. Thermospheric dynamics are predominantly driven by temporal variations and spatial distributions of solar irradiance, geomagnetic forcing, redistributed composition and energy within the thermosphere. Variations in the external forcing, internal dynamics of the system, and coupling between the thermosphere and ionosphere, can drive complicated neutral temperature and composition variations, which varies neutral density scale heights and causes complicated density variations. Temporal variations include abrupt changes with a time scale of minutes to hours, diurnal variation, multi-day variation, solar- rotational variation, annual/semi-annual variation, solar-cycle variation, and long-term trends with a time scale of decades and spatial variations include latitudinal and longitudinal variations, as well as variation with altitude. In this study, we discuss and summarize these density variations from atmospheric density data, measured by accelerometers on-board the Swarm satellite. This research has the potential to improve atmospheric density modeling using Swarm accelerometer level2 data.
9:15am - 9:30am
Swarm Mass Density and Plasma Observations During the St. Patrick's Day Storm Event 2015 and its Global Numerical Modelling Challenges
1GFZ German Research Centre for Geosciences, Germany; 2Delft University of Technology, Faculty of Aerospace Engineering, The Netherland; 3Institut de Physique du Globe de Paris, France
The most severe geomagnetic storm in solar cycle 24 started with a sudden storm commencement (SSC) at 04:45 UT on St. Patrick's day March 17, 2015. It occurred without any significant precursor X- or M-type solar flares and appeared as a two-stage geomagnetic storm with a minimum SYM-H value of -233 nT.
In the response to the storm commencement in the first activation, a short-term positive effect in the ionospheric vertical electron content (VTEC) occurred at low- and mid-latitudes on the dayside.
The second phase commencing around 12:30 UT lasted longer and caused significant and complex storm-time changes around the globe with hemispherical different ionospheric storm reactions in different longitudinal ranges.
Swarm-C observations of the neutral mass density variation along the orbital path as well as Langmuir probe plasma measurements of all three Swarm satellites and global TEC records during the storm interval are used for physical interpretations and modelling of the positive/negative storm scenario.
At mid-latitudes, positive storm signatures were observed in the Northern Hemisphere (NH) of the European sector, whereas a large positive storm occurred in the Southern Hemisphere (SH) of the American sector. The negative storm phase was found to be strongest in the Asian sector, in particular in the NH, but developed globally on March 18 at the beginning of the recovery phase.
These observations pose a challenge for the global numerical modelling of thermosphere-ionosphere storm processes as the storm, which occurred around spring equinox, obviously signify the existence of other impact factors than seasonal dependence for hemispheric asymmetries to occur. First numerical simulation trials using the Potsdam version of the Upper Atmosphere Model (UAM-P) are presented to explain these peculiar ionospheric storm processes.
9:30am - 9:45am
Detection of Thermospheric Density Variations via Spacecraft Accelerations Observed Using the CASSIOPE GAP Instrument
University of New Brunswick Geodesy and Geomatics Engineering
As one of eight instruments of the Enhanced Polar Outflow Probe (e-POP) payload on the Canadian CAScade, Smallsat and IOnospheric Polar Explorer (CASSIOPE) small satellite, the GPS Attitude, Positioning, and Profiling experiment (GAP) can employ one or more of the four GAP-A dual-frequency GPS receivers and associated zenith-facing antennas to provide high-resolution spatial positioning information, flight path velocity determination, and real-time, high-stability timing. Preliminary processing of raw GPS data acquired from one of the GAP-A GPS receivers using the University of New Brunswick’s GNSS Analysis and Positioning Software (GAPS) precise point positioning (PPP) utility has produced sub-decimetre root-mean-square positions and correspondingly accurate velocities for the CASSIOPE spacecraft. Spacecraft acceleration can also be determined by subsequent processing of the velocity estimates. To further enhance the precision and accuracy of CASSIOPE position, velocity, and acceleration estimates, the creation of a specialized low-Earth-orbit PPP processing engine is currently under development. This improved processing engine will be used to produce high-accuracy time series of CASSIOPE’s orbit, thus allowing for analysis of the spacecraft’s long-term orbital evolution as it approaches atmospheric re-entry. The proposed software will also allow for precise determination of short timescale accelerations of the spacecraft through the differencing of sequential high-rate velocity estimates using an appropriate filter. These precise acceleration determinations can subsequently be used to infer density variations in the thermosphere via algorithms previously developed within the SWARM science data system.