a Atmospheric, Oceanic and Planetary Physics, University of Oxford, Parks Road, Oxford OX1 3PU, UK

1
Use of HIRDLS Data to Measure Stratospheric and
Mesospheric Gravity Waves
CORWIN J WRIGHTa, JOHN J BARNETTa, JOHN C GILLEb
HIRDLS
The High-Resolution Dynamics Limb Sounder is a
21-channel infrared filter radiometer on NASAs
Aura platform 1,2. Shortly after launch, the
instrument suffered a partial failure, most
probably due to a sheet of Kapton thermal
blanketing material coming loose. Extensive work
has been undertaken to correct for this, and it
is believed that good results can be obtained for
most of the atmosphere 3,4.
Figure 1 artists impression of Aura. The strong
yellow line shows the view of HIRDLS
Figure 2 artists impression of the obstructed
view from HIRDLS
METHOD
Figure 3 plot showing an atmospheric temperature
profile (black) and the same profile convolved
with a Gaussian of FWHM 5km.
Due to the strong dependence of atmospheric
temperature on height, it is difficult to
directly observe small-scale features such as
gravity waves. Accordingly, we need first to
high-pass filter the data, removing the
smoothly-varying background to highlight
perturbations to the background state 5. This
is done by convolving a sequence of temperature
profiles with a Gaussian at a given altitude, and
then subtracting this from the original data to
highlight the differences (figure 3).
The perturbation data is then fed into a 2D FFT
routine in chunks of 40 profiles stepped by 10
profiles, to analyse the data for regular
periodic features. Those with a strongly periodic
feature with a Fourier coefficient one standard
deviation or higher over a mean calculated for
all data available are then highlighted, and any
sequence of three or more positive results
highlighted as a positive gravity wave result
(figure 4) for analysis.
RESULTS
Preliminary work on the detected waves has been
focused on a number of key areas. The first of
this was to compare the overall results to those
in the scientific literature as a sanity check.
Figure 5 shows results obtained from the 2D
detector compared to those obtained from UARS MLS
measurements of saturated limb variances 6 from
1992 - 1997, and demonstrates excellent agreement
between the two studies. The same agreement is
observed in other comparisons, providing further
reinforcement of this.
Analysis has been performed using data simulating
the HIRDLS orbital track via ECMWF data, and
results from processing of this give a very small
number of randomly-scattered results, as would be
expected. Therefore, it can be assumed
confidently that the method is sound, allowing
analysis of the physical processes involved to be
undertaken with confidence.
Figure 5 comparison of our results (top) against
results from 6 (bottom). The left-hand plots
describe northern-hemisphere winter and the
right-hand plots southern-hemisphere winter
FUTURE WORK
Significant future work will be undertaken to
further expand the work described above -
comparison with other high-resolution data
(sondes, GPS, Aura MLS) with temporal and spatial
overlap to confirm results - analysis of the
surrounding atmosphere, using, for example, wind
speed data from the ECMWF - analysis of gravity
wave formation and breaking - study of similar
small-scale phenomena, such stratospheric
temperature enhancements
REFERENCES
1 Gille et al, 2003 The High Resolution
Dynamics Limb Sounder (HIRDLS) Experiment on
Aura. Proc. SPIE, 5152, 162171. 2 Hepplewhite
et al, 2005 HIRDLS Functional Performance in
Orbit - A Summary. Proc. SPIE, 5883, J1J10. 3
Barnett et al, 2005 Mapping the optical
obscuration in the NASA Aura HIRDLS instrument.
Proc. SPIE, 5883, I1 I10. 4 Schoeberl et al,
2006 Overview of the EOS Aura Mission. IEEE
Trans. Geophys. and Remote Sensing, 44,
10661074. 5 Eckermann and Preusse, 1999
Global Measurements of Stratospheric Mountain
Waves from Space. Science, 286, 15341537. 6
Jiang et al, 2003 Mountain Waves in the Middle
Atmosphere MLS Observations and Analyses. Adv.
Space Res., 32, 801806.
a Atmospheric, Oceanic and Planetary Physics,
University of Oxford, Parks Road, Oxford OX1 3PU,
UK b Center for Limb Atmospheric Sounding,
University of Colorado at Boulder, Boulder, CO
80301, USA. contact wright_at_atm.ox.ac.uk