PRELIMINARY VALIDATION OF IAPP MOISTURE RETRIEVALS
USING DOE ARM MEASUREMENTS
UW-Madison
Wayne Feltz, Thomas Achtor, Jun Li and Harold Woolf
Cooperative Institute for Meteorological Satellite Studies (CIMSS), University of Wisconsin- Madison
INTRODUCTION
Comparison of Moisture Profile Calculations from IAPP
and SGP Radiosondes
Global atmospheric temperature and moisture retrievals from the Advanced TIROS
Operational Sounder (ATOVS) radiance data are produced routinely at CIMSS
using the International ATOVS Processing Package (IAPP). (See lower center
panel for more details on IAPP software.) The University of Wisconsin - Madison
Space Science and Engineering Center (SSEC) has a downlink capability to
acquire global ATOVS radiances in near real-time for IAPP processing.
•
Validation Source: Co-located SGP central facility radiosonde moisture profiles
•
Satellite Product: ATOVS IAPP derived moisture profiles, using surface
observations and AVN model first guess
•
To assess the accuracy of the IAPP retrievals, comparisons are made to
measurements from the U. S. Department of Energy (DOE) Atmospheric Radiation
Measurement (ARM) Program site in the U. S. Southern Great Plains (SGP) (see
http://www.arm.gov/). A study to create the comparison data set was started in
September 2001. The IAPP moisture output is compared to spatially and
temporally co-located radiosonde and microwave radiometer (MWR) data at the
ARM site. A case study example of a cold frontal passage is also presented.
DOE ARM Southern Great Plains Instrument Site
Above are two examples from the comparison data set. Each diagram shows
the temperature and moisture profiles for the radiosonde (black), the Aviation
Model first guess (red) and the final IAPP physical retrieval (blue). The IAPP
retrieval improves upon the AVN first guess when compared to the radiosonde
validation source, especially in the upper troposphere.
• Satellite Products: ATOVS IAPP Temperature and Moisture Fields
On 12/5/01 a cold front moved
through the SGP ARM site
domain. A ground-based AERI
instrument located at the SGP
central facility retrieved boundary
layer temperature and moisture
structure during this frontal
passage.
A time-height cross
section
of
AERI
potential
temperature and water vapor
mixing ratio indicate rapid
cooling and drying around 1900
UTC. Wind barbs from the NOAA
404 MHz wind profiler near
Lamont, Oklahoma are plotted on
the upper cross section. The
wind profiler indicates the frontal
passage, as winds veer from
southwest to northwest.
This
case can also be examined using
ATOVS temperature and moisture
profiles as shown below.
In the early morning, the SGP
central facility was in the warm
sector with southerly winds
and 15C dewpoint.
The
radiosonde profile indicates a
cloud at 750 hPa at 1130 UTC;
the ATOVS profile from 2 hours
earlier indicates cirrus clouds.
The satellite image from 1445
UTC shows the high clouds
east of the site which are
indicated by the ATOVS profile
from 0930 UTC.
Microwave Radiometer (MWR)
Comparison of Total Precipitable Water Vapor (TPW)
Calculations from IAPP and MWR
• Validation Source: DOE SGP Microwave Radiometer (MWR) Total Precipitable
Water Vapor (TPW)
• Satellite Product: ATOVS IAPP derived TPW, using surface observations and
AVN model first guess
• Co-location criteria: 5 minutes and 1/2 degree lat/lon.
The improvement in water vapor profiles can be shown statistically with 59
coincident radiosonde - ATOVS matches. This figure shows the mean bias (left)
and the RMS difference (right) for the Aviation Model first guess (red) and the
IAPP final physical retrieval (black) when compared with coincident
radiosondes. A 50% improvement in bias and a 25% improvement in RMS is
indicated in the IAPP moisture retrieval in the mid and upper troposphere,
largely due to a moist bias in the model.
Further Information on the
International ATOVS Processing Package (IAPP)
The scatter plot compares MWR total water vapor values to the AVN model forecast (red
triangles) and the IAPP ATOVS physical retrieval values (black stars). RMS and bias values for
205 temporal and spatial matches are shown.
IAPP physical retrievals show modest
improvement over the AVN model TPW first guess in mean difference (0.1 mm or 5%) and better
improvement in RMS (0.4 mm or 12%). IAPP physical retrievals indicate good accuracy when
compared to MWR measurements, especially considering the different spatial characteristics of
the measurements.
• Validation Source: Radiosondes, AERI (Atmospheric Emitted Radiance Interferometer)
Co-location criteria: 1 1/2 hours and 1 degree lat/lon
Participation within the ARM program has allowed independent, high quality
validation opportunities for satellite derived products.
Location of DOE ARM site
Cold Frontal Passage Example Demonstrating ATOVS
Vertical Temperature and Moisture Retrievals with DOE
ARM Measurements
•
The IAPP uses radiances from HIRS/3 and AMSU -A and -B, preprocessed using the
AAPP to level 1-D format, for retrieval.
•
The retrieval algorithm is a physical simultaneous technique described by Li et al., 1998,
10th Proceedings of the International TOVS Study Conference, Boulder, CO.
•
To obtain IAPP source code, contact tom.achtor@ssec.wisc.edu.
At 1730 UTC (11:30 CST) both
profiles (although still 2 hours
apart) indicate the boundary
layer moisture has decreased
while the temperature profiles
indicate warm boundary layer
conditions still exist. Surface
data and the satellite image
indicate the cold front is
approaching
the
central
facility site.
Near 0000 UTC the cold front
has cleared the central
facility.
Note the cooling
within the boundary layer and
the drying through the entire
atmospheric column.
The
surface data from 2200 UTC
indicates temperatures over
17C, while the radiosonde
profile from a later time
shows
the
nocturnal
inversion developing.
Acknowledgments: The work has been supported through NOAA grant NA67EC0100. The AERI, MWR, and radiosonde
data were obtained from the Atmospheric Radiation Measurement (ARM) program sponsored by the U.S. Department of
Energy, Office of Science, Office of Biological and Environmental Research, Environmental Sciences Division.