1. Measurements

1
TOMS Ozone Observations and their Applications in
Weather Forecast Wu Y.-H., X. Zou and K-Il Jang
1. Measurements TOMS (Total Ozone Mapping
Spectrometer) is part of NASA's mission to study
the Earth as a global environmental system (Fig.
1). TOMS instrument is a second generation
backscatter ultraviolet ozone sounder. It is used
to measure the total amount of ozone in a
"column" of air from the Earth's surface to
the top of the atmosphere under all daytime
observing and geo-physical conditions. There are
almost 200,000 daily TOMS ozone measurements
covering the entire Earth outside the polar
night region.


TOMS/Nimbus-7 is the first TOMS instrument to
provide reliable maps of global ozone amounts on
a daily basis from November 1978 to May 1993.
Since then three other satellites with TOMS
instruments have been launched. They are
Meteor-3 (the former Soviet Unions satellite) in
operation from August 1991 to December 1994,
ADEOS (Japanese satellite) launched on August 17,
1996 , which provided data until June 29, 1997,
and NASA's Earth Probe satellite launched on July
2, 1996, which continues to provide high
resolution total column ozone data.
Fig.3 Linear relationship between TOMS ozone
and mean integrated potential vorticity
Fig. 4 Correlation between TOMS ozone and SLP
within the central region of Erin
Fig, 5. Bogus SLP constructed from TOMS ozone for
hurricane Erin on Sep. 9, 2001
4.Applications 4.1 TOMS ozone data were used to
construct the SLP within the central region of
hurricane to derive the asymmetric
structure (Fig. 5) which is comparable to that of
visible image (Fig. 6). 4.2 TOMS ozone data were
also assimilated into the mesoscale model MM5 to
improve the prediction of winter storms
(Jang et al. 2003). The basis of the
assimilation technique was a statistical model
utilizing a strong correlation between
vertical mean potential vorticity (MPV) and TOMS
ozone in middle latitudes. The TOMS ozone
was incorporated in a four-dimensional
variational data assimilation (4D-Var)
procedure and applied to the prediction of the 24
- 25 January 2000 East Coast winter
storm. There was almost no impact on the
prediction of storm development when the
adjustments in model initial conditions resulted
from assimilating only TOMS column ozone data
that are confined to the upper levels.
However, forecasts are improved when TOMS ozone
data are used together with radiosonde
observations (BOTH, Fig. 7). It is expected that
for cases in which sensitivities in the
upper troposphere are large, inclusion of TOMS
data alone may significantly impact
forecasts.
Fig.1 Schematic TOMS instrument from NASA
2. Deriving ozone TOMS measures the total column
ozone by means of the backscattered ultraviolet
(BUV) technique. Its principle can be stated as
follows TOMS measures both incident solar
irradiance and the BUV radiation. For determining
total column ozone, two pairs of measurements
are made. One is made at a wavelength that is
strongly absorbed by ozone. The other is made at
a wavelength that is weakly absorbed by ozone.
The measurements of incoming UV irradiance and
backscattered UV radiance at the weakly absorbing
wavelength tells us how much BUV light we would
expect from the measurement if there was no ozone
absorption. At the other wavelength the UV light
is continuously being absorbed by ozone as it
passes through the atmosphere along the light
path. Differences between these measurements made
at the two wavelengths are used to infer the
amount of ozone present in the atmosphere. In
fact, in order to obtain the most accurate ozone
measurements at different geographical locations
and weather situations, six pairs of measurements
at different optimal wavelengths are made near
the UV bands. Figure 2 shows the daily TOMS
ozone distribution on Nov. 4, 2003.
The advantage of the BUV technique is that by
looking directly down at the atmosphere below in
a viewing geometry called nadir viewing, the
satellite is able to get a good horizontal
resolution (40X40 km). The main disadvantage of
the BUV technique is that the effects of
increased multiple scattering and reduced
sensitivity to the shape of the profile lead to
poor total column ozone estimates.
Fig. 6 Visible image of hurricane Erin on Sep. 9,
2001 from NASA Terra satellite
Fig. 7. SLP (solid) and vertically integrated
cloud water (dotted) and rainwater (shaded) at 12
UTC 25 Jan 2000 for CTRL (left) and BOTH (right).
Fig. 2 TOMS total ozone on Nov. 4, 2003
3.Meteorological information contained in ozone
data Since the pioneering work of Dobson and
collaborators (1928, 1946), the strong
correlation between total ozone and some
meteorological quantities, such as the mean
integrated potential vorticity (Fig.
3), temperature, tropopause height, and sea level
pressure (SLP) (Fig. 4) have been revealed. The
meteorological significance of the TOMS ozone
observations has drawn more and more interests in
numerical weather prediction in recent years.
References 1. McPeters, R.D., P. K. Bhartia, A.
J. Krueger, and J. R. Herman, 1998 Earth Probe
TOMS data product users guide. NASA
Tech. Publ. 1998-206895, 70pp. 2. Jang, K.I., X.
Zou, M.S.F.V. De Pondeca, M. Shapiro, C. Davis,
and A. Krueger, 2003 Incorporating TOMS ozone
measurements into the prediction of the
Washington , D. C., winter storm during24-25
January 2000. J. Appl. Meteor., 42, 797-812