Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics/Global Ultraviolet Imager (TIMED/GUVI)

ars_thumb The NASA TIMED satellite carries four instruments for measuring solar extreme ultraviolet (EUV) irradiances, winds, temperature, auroral energy inputs, and composition. One of these is a far ultraviolet spectrographic imaging instrument (GUVI) that is very similar in design to the Defense Meteorological Satellite Program (DMSP) Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instruments. CPI's involvement in GUVI was through algorithm development and Dr. Douglas Strickland's participation on the GUVI science team as a co-investigator. Additional support came through a TIMED/CEDAR grant to Dr. James Hecht of the Aerospace Corporation whose focus has been comparison of auroral data products from coincident ground-based and GUVI measurements. Key data products come from CPI remote sensing algorithms similar to those previously developed for the SSUSI instrument (dayglow algorithms; auroral algorithms).

Products include:

References to published work with CPI involvement may be seen on our publications page under Space Weather. These include Christensen et al. [2003], Strickland et al. [2004 - two papers], Meier et al. [2005], Crowley et al. [2006], and Strickland et al. [2007].

One of the above papers (Strickland et al. [2004a]) addresses seasonal effects on O/N2 between hemispheres under geomagnetically quiet conditions (Figure 1) and the sensitivity of O/N2 to Lyman-Birge-Hopfield (LBH) cross section uncertainties and to solar EUV/XUV scalings shortward of 20 nm.

Figure 1a. (Plate 1 from Strickland et al. [2004a]) GUVI and NRLMSIS O/N2 on days 76 (3/17/02), 196 (7/15/02), 264 (9/21/02), and 16 (1/16/03). Quiet geomagnetic conditions prevail on these days for which daily Kp is less than two. The time scales illustrate the fact that ~24 hrs of data were used to produce the GUVI images. Local times throughout the images at low latitudes are near noon. The selected dates serve to illustrate O/N2 behavior under near-equinox and near-solstice conditions.

Key results from the second of the above 2004 papers (Strickland et al. [2004b]) include the effect of solar flares on QEUV as seen in its variation over the mid-July to early-August 2003 solar rotation (Figure 2). The results show excellent agreement with the Solar and Heliospheric Observatory/Solar EUV Monitor (SOHO/SEM) solar EUV data in a relative sense over the rotation (include spikes due to flares), as well as the sensitivity of QEUV to LBH cross section uncertainties and the solar EUV/XUV scalings shortward of 20 nm (similar to the sensitivity of O/N2 addressed in the above paper).

Figure 2. (Figure 4 from (Strickland et al. [2004b]) GUVI QEUV values are compared in a) with a linear parameterization of SOHO SEM central channel data. SEM and GOES X-ray data are shown at 5-minute time resolution in b).

CPI provided the GUVI O/N2 results appearing in the above Meier et al. [2005] and Crowley et al. [2006] papers. These include the spectacular variations on Nov 20-21 2003 during a major geomagnetic storm from that period (Figure 3). The reduced O/N2 over very extended geographical regions arose from atmospheric heating within the auroral oval over many hours followed by transport of heated (and compositionally disturbed air) in the midnight sector to lower latitudes by winds arising from the storm. It was then observed by GUVI many hours later on the dayside.

Figure 3. O/N2 during the super storm that commenced on Nov 20 2003. Local time throughout the image is near noon. The time axis illustrates that 24 hours of data were used beginning mid-day on Nov 20. The dark regions contain disturbed air that is strongly deficient in atomic oxygen. Such regions remain in this state for many hours and contain a seriously depleted ionosphere (referred to as a negative ionospheric storm).

In an investigation described in detail by Strickland et al. [2007], we are using GUVI 135.6 [134.3 - 137.7 nm] and LBHS [141.0 - 152.8 nm] dayglow measurements recorded during solar flares to estimate the spectrum of solar EUV/XUV irradiances. An entirely new algorithm has been developed beyond that documented in the above 2004 QEUV paper. It relies on TIMED/SEE measurements longward of 27 nm and derives the spectrum at shorter wavelengths with the constraint that the full spectrum replicate the coincident GUVI measurements. Derived spectra are tested by using them to produce E-layer electron density profiles (EDPs) with the AURIC model followed by comparisons with measured EDPs. Overall good agreement is achieved for solar flares addressed so far (X-class flares on Oct 28 and Nov 4 2003). Figure 4 is taken from the 2007 paper and shows the significant increase in dayglow during these flares and other information as discussed in the caption.

Figure 4. Left stack of panels: preflare and flare GUVI nadir data, QEUV, and O/N2 versus latitude from Oct 28 (revs 10218 [preflare] and 10219[flare]). Right stack: similar to the left stack but for Nov 4 (revs 10327 [preflare] and 10328 [flare]). The data (Version 8) have been scaled by 1.2 as recommended by APL based on stellar calibrations. Time scales at the bottom refer to the flare revs. O/N2 and QEUV during the flares are underestimated due to the use of a non-flare lookup table to derive these quantities for the flare revs (as well as the preflare revs). The disagreements between preflare and flare QEUV (they should be approximately the same) illustrate the need for harder EUV spectra to derive this quantity during the two flares. Such spectra are now being derived with CPI's new flare algorithm using a combination of GUVI and SEE data (SEE spectral measurements > 27 nm).

There was also an active investigation directed to auroral remote sensing using the three GUVI spectral channels 135.6, LBHS, and LBHL [167.2 - 181.2 nm] from which Eo, Q, and O/N2 were derived. Much of the work was in collaboration with J. Hecht of the Aerospace Corporation who has and continues to operate ground-based photometer systems at Poker Flat and Ft. Yukon, AK. The data from these systems are also used to derive Eo, Q, and O/N2. Interest has been in the comparison of products from coincident data. GUVI products for many passes through the auroral oval (Northern Hemisphere) have been produced in image form and as plots from cuts through these images. This work is presently unpublished.