EstimatingDstindices and exospheric temperatures from equatorial magnetic fields measured by DMSP satellites

Abstract

[1] We explore the feasibility of using variations in the horizontal component (DB H ) of the Earth's magnetic field as measured by DMSP satellites while crossing the dip equator to estimate the provisional Dst index and the state of the thermosphere in near real time. Equatorial crossings are identified as locations where the vertical component of the main field measured by DMSP satellites vanishes. Local differences between measured and IGRF (epoch 2005) horizontal components (dB H ) were calculated for the years 2005 to 2009. Each year quiet time (0 ≥ Dst ≥ -7 nT) subsets of dB H were identified to establish offset baselines (dB H B ) as functions of longitude along the magnetic equator ( eq ) for each spacecraft. Year-to-year changes in dB H B reflect variations of the Earth's main field, indicating that baseline calculations must be updated at regular intervals for each spacecraft. Running-averaged values of DB H (t) = dB H ( eq , t) − dB H B ( eq , t) inferred from combined DMSP F16 and F17 data streams are shown to follow variations in Dst during the test interval. The method is also shown to apply during the magnetic superstorms of late 2003. Except during the late main phase, increases in globally averaged exospheric temperatures inferred from DB H and provisional Dst time series are in reasonable agreement with those inferred from measurements by accelerometers on the GRACE satellites.

Predicting global average thermospheric temperature changes resulting from auroral heating

“…As the future continuity of upstream solar wind and IMF measurements is not guaranteed, the derivation of the corrections from the Dst index could be useful as a backup. Efforts are underway to derive a real-time substitute for the traditional method for deriving Dst [Burke et al, 2010]. The original JB2008 model had previously been tested through comparisons with drag information from radar and optical tracking of 75 to 80 inactive "calibration satellites" [Bowman et al, 2008a].…”

“…A concise summary of these results is provided by Burke et al [2010]. Models of the thermosphere other than J77 may produce different results.…”

“…[3] In 2009, the Iridium 33 communication satellite was destroyed by collision with a nonoperational satellite (Cosmos 2251), appreciably increasing the debris in Earth's orbit [Burke et al, 2010]. The proliferation of space debris results in a requirement for improved capabilities for predicting the state of the thermosphere at any given time.…”

Solar cycle dependence of solar wind energy coupling to the thermosphere

“…Sutton [2009] recalibrated the GRACE accelerometers in flight, and applied this calibration to all measurements acquired between launch in mid-2002 and the end of 2008. Figure 9 of Burke et al [2011] shows that during the common period in 2004 the UTX and Sutton calibrations were highly correlated. UTX calibrations produced systematically higher densities than did Sutton's.…”

“…Both parameters are higher near solar maximum than near solar minimum. Burke et al [2011] pointed out that T ∞ SW peaks near times of main-phase minima in Dst when time derivatives in equations (2) and (3) vanish. Thus,…”