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HIRS Pathfinder clear-sky comparison

A comparison of version 1 and version 2 clear-sky data is presented here. Several changes were made in the version 2 processing.

• Revised limb correction is done for channel 8 that allows for more clear-sky detection of far limb observations. Limb correction coefficients do not include near-IR channels as was done in verion 1.
• Revised cloud detection method helps eliminate many of the persistent clouds seen in the tropical convection areas. This revisions include (1) a threshold test for all limb corrected channel 8 brightness temperatures equatorward of 15 degrees and (2) long-term statistics files (5-,15-,35-day) are better centered around the day of observation.
• Include data over high terrain and near the Poles.
• Time series now extends through December 2001.
• Cloud information is now available with the version 2 data using CO2 slicing method from Don Wylie at SSEC. This information includes cloud top height, cloud top pressure, and cloud emissivity.

Cloud contamination comparison

The table below gives comparisons between version 1 and version 2 for various cloud regions where persistent cloud cover contaminated the clear-sky product for version 1. Three tropical regions were selected that contain persistent cloud cover. Mean and standard deviation fields are given for channel 5. This channel is a tropospheric temperature channel that is sensitive to middle and upper tropospheric clouds (indicated by relative cold brightness temperature). Generally the temperatures are warmer in version 2 data and the standard deviation is less.

Table1: Cloud Contamination comparison

Satellite	India	Indonesia	Amazon
N11		HIRS 5 mean 01/1993 HIRS 5 stddev 01/1993
N12			HIRS 5 mean 01/1993 HIRS 5 stddev 01/1993
N14	HIRS 5 mean 01/1993 HIRS 5 stddev 01/1993		HIRS 5 mean 01/1993 HIRS 5 stddev 01/1993
N15

Monthly comparison

Differences between selected monthly mean grid maps are shown here.

Table 2: Monthly mean difference

satellite

CHN 1

CHN 2

CHN 3

CHN 4

CHN 5

CHN 6

CHN 7

CHN 8

CHN 9

CHN 10

CHN 11

CHN 12

CHN 20

N11

HIRS 1 mean 07/1996"

HIRS 2 mean 07/1996"

HIRS 3 mean 07/1996"

HIRS 4 mean 07/1996"

HIRS 5 mean 07/1996"

HIRS 6 mean 07/1996"

HIRS 7 mean 07/1996"

HIRS 8 mean 07/1996"

HIRS 9 mean 07/1996"

HIRS 10 mean 07/1996"

HIRS 11 mean 07/1996"

HIRS 12 mean 07/1996"

HIRS 20 mean 07/1996"

N12

N14

N15

Time series comparison

Time series for selected latitude bands are shown here. Solid curve indicates version 2 results.

Table 3: Time series latitude band difference

Satellite	Time	CHN 4	CHN 8	CHN 12
N11	(1/92-12/94)	15N-15S 30N-30S 30N-60N	15N-15S 30N-30S 30N-60N	15N-15S 30N-30S 30N-60N
N12	(1/92-3/97)	15N-15S 30N-30S 30N-60N	15N-15S 30N-30S 30N-60N	15N-15S 30N-30S 30N-60N
N14	(2/95-12/99)	15N-15S 30N-30S 30N-60N	15N-15S 30N-30S 30N-60N	15N-15S 30N-30S 30N-60N
N15	(11/98-12/99)	15N-15S 30N-30S 30N-60N	15N-15S 30N-30S 30N-60N	15N-15S 30N-30S 30N-60N