MSU Ch 3/4 Daily Upper Troposphere Temps with Limb93 Correction V001 (MSUUTT) at GES DISCEntry ID: GES_DISC_MSUUTT_V001
Abstract: Section 1. General Description
Spencer and Christy (1990) demonstrated that accurate estimates of global
atmospheric temperatures could be derived from the Microwave Sounding Units
flown on NOAA's TIROS-N series of satellites. ... The MSU's have been
continuously operating for more than 14 years collecting measurements of the
thermal emission of radiation by molecular oxygen at four frequencies near 60
The four MSU channels have contribution functions (CF's) determined by their
wavelength and the atmospheric profile of oxygen. MSU channel 1 has a CF peak
near the surface, and is influenced strongly by temperature and liquid water
near the surface. The channel 2 CF is dominated by a wide peak near 50 kPa.
Channel 3 peaks near the tropopause (25 kPa) and the Channel 4 CF has a
somewhat sharper peak in the lower stratosphere (7 kPa).
Spencer and Christy (1992 a,b) demonstrated that the MSU calibrations have been
very stable, with a precision of monthly satellite measurements of 0.01 deg C
for the global mean.
A. 3/4 Upper Tropospheric Retrieval.
Spencer has developed a procedure for calculating the temperature of the upper
troposphere in the tropics using MSU Channels 3 and 4. This Channel 3/4 CF has
a peak in the upper troposphere near 25 kPa. Because the 3/4 CF straddles the
mid-latitude tropopause, this product is only calculated for the tropical
latitudes between 30 S and 30 N. The influence of calibration drifts in
channel 3 on several MSU instruments are present in the 3/4 time series, and
therefore the upper tropospheric temperature product may not be useful for
monitoring long-term trends. The 3/4 retrieval algorithm screens the data to
remove calibration differences between satellites along with the effects of
precipitation size ice particles, and corrects for the effect of changing earth
incidence-angle across a scan line (Limb93). The data have been inter
calibrated to correct for differences between local orbit crossing times (e.g.,
2:30 a.m. vs. 7:30 a.m.), and diurnal differences (a.m. vs. p.m.). As a last
step, the algorithm screens out known bad data points found during an
exhaustive analysis of the entire data set.
B. MSU Calibration.
The Limb93 Ch 3/4 retrievals use calibrated MSU data. The MSU brightness
temperatures for all four channels were linearly calibrated using the
radiometric counts measured viewing the earth scene as compared to the
difference between the radiometric measurement while viewing a warm calibration
load and a similar view of deep space (assumed to be 2.5K). For information on
the calibration procedure, the user is referred to the TOVS MSU Pathfinder
Section 2. MSU LIM93 Data File Structure
The Limb93 data files are given in HDF structure. Every file contains 365
Scientific Data Sets (366 for leap years), one for each day of the year. Each
SDS contains a two dimensional data set, the x dimension is longitude and the y
dimension is latitude. The grid is composed of 144 (longitude) by 72
(latitude) 2.5 by 2.5 degree grid boxes. The first grid box is centered at
78.75 N 178.75 W. The data structure for the SDS data is int16, and the data
are given in hundreths of Kelvin degrees. Data for grid boxes outside the
tropics (30 S to 30 N) are denoted as missing, because the increasing
stratospheric influence invalidates the 3/4 limb correction.
Section 3. Algorithm Description
Upper Troposphere Deep Layer Mean Temperature (UTT).
The SDS's contain the upper tropospheric temperature parameter (Ch 3/4) for the
tropical areas which is derived using a linear combination of MSU channels 3
3/4 Tb = 1.35 * Tb3 - .35 * Tb4
where, Tb3 refers to the brightness temperature in MSU channel 3 and Tb4 the
brightness temperature in MSU channel 4.
The 3/4 retrieval is calculated for each footprint of the MSU scan line, the
latitude and longitude of the footprint are calculated and the appropriate limb
correction (Limb93) is applied based on latitude, longitude, month, and scan
angle. Next, the footprint data are assigned to the appropriate grid box.
Data for areas outside the tropics have been set as missing. The data are
intercalibrated to remove differences in the instruments on the different
satellites, differences due to orbit geometries (7:30 a.m. vs 2:30 a.m.
satellites), and diurnal differences (a.m. vs. p.m. orbits). After the a.m.
and p.m. orbits are processed, a horizontal interpolation is used to fill some
of the empty grid boxes.
(Click for Interactive Map)
Data Set Citation
Dataset Originator/Creator: Hugo Ahlenius
Dataset Title: Arctic temperatures in the 20th century, modeled and observed.
Dataset Release Date: June 9, 2010
Dataset Publisher: UNEP/GRID-ArendalOnline Resource: http://maps.grida.no/go/graphic/arctic-temperatures-in-the-20th-cen...
Start Date: 1900-01-01Stop Date: 2000-12-31
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Wang, M., Overland, J.E., Kattsov, V., Walsh, J.E., Zhang, X. and Pavlova, T. (2007). Intrinsic versus forced variation in coupled climate model simulations over the Arctic during the 20th century. J. Climate, 20(6), 1093-1107
UNEP/GRID-Arendal, Arctic temperatures in the 20th century, modeled and observed, UNEP/GRID-Arendal Maps and Graphics Library, http://maps.grida.no/go/graphic/arctic-temperatures-in-the-20th-cen... (Accessed 9 June 2010)
Creation and Review Dates
DIF Creation Date: 2010-06-09
Last DIF Revision Date: 2010-06-09