Upper Tropospheric Humidity: A Comparison of Satellite, Upper Tropospheric Humidity: A Comparison of Satellite, Radiosonde, Lidar and Aircraft MeasurementsRadiosonde, Lidar and Aircraft Measurements

Satellite

Lidar

Aircraft

Radiosonde

CollaboratorsCollaborators

Rich Ferrare et al., NASA/LaRCRich Ferrare et al., NASA/LaRC

John Goldsmith, DOE/LANLJohn Goldsmith, DOE/LANL

Barry Lesht, DOE/ANLBarry Lesht, DOE/ANL

Larry Milosevich, NCARLarry Milosevich, NCAR

Frank Schmidlin, NASA/GSFCFrank Schmidlin, NASA/GSFC

Bill Smith et al., NASA/LaRCBill Smith et al., NASA/LaRC

Dave Tobin et al., Univ. of WisconsinDave Tobin et al., Univ. of Wisconsin

Dave Turner, DOE/PNNLDave Turner, DOE/PNNL

David Whiteman et al., NASA/GSFCDavid Whiteman et al., NASA/GSFC

ObjectiveObjective

To assess of the accuracy of current To assess of the accuracy of current

measurements of upper tropospheric water vapor.measurements of upper tropospheric water vapor.

Assuming: Assuming:

a) There is no perfect observation of upper tropospheric water vapor. a) There is no perfect observation of upper tropospheric water vapor.

b) We should assess the b) We should assess the consistencyconsistency of different measurements, rather of different measurements, rather than attempting to than attempting to validatevalidate against a specific benchmark. against a specific benchmark.

c) Satellites can provide a common reference for comparing disparate c) Satellites can provide a common reference for comparing disparate measurements to assess their measurements to assess their relativerelative consistency. consistency.

Why Monitor Upper Tropospheric Water Vapor?Why Monitor Upper Tropospheric Water Vapor?

Change in Water Vapor at 2xCOChange in Water Vapor at 2xCO22: GFDL GCM: GFDL GCM

Increase in tropopause RHamplifies wv feedback by ~10%

Most change attributable to increase in saturation vapor pressure

Satellite Measurement of Upper Tropospheric HumiditySatellite Measurement of Upper Tropospheric Humidity

What do IR “water vapor” radiances measure?What do IR “water vapor” radiances measure?

•The 6.7 m radiances are sensitive to relative humidity averaged over a deep layer of the upper troposphere (~200-500 hPa).

* Use satellite 6.7 m Tb to

provide a common, stable benchmark for intercomparing other measurements.

Step 1: Insert lidar/sonde moisture profile (and coincident sonde temperature profile) into radiative transfer model.

* Compare observed and forward-simulated Tb.

How do you compare satellite measurements How do you compare satellite measurements with a water vapor profile?with a water vapor profile?

Step 2: Transform both observed and simulated Tb into

Upper Tropospheric relative Humidity (UTH)

ln (UTH p0/ cos) = a + b T

6.7 (1)

* Use UTH translation to interpret Tb comparison.

1 K error in Tb equals ~10% relative error in UTH.

"Profile-to-Radiance" Comparison Procedure"Profile-to-Radiance" Comparison Procedure

0 100 %UTH HighCloud

6.7 m Tb

UTH TransformationUTH Transformation

Global Comparison of Satellite and RadiosondesGlobal Comparison of Satellite and Radiosondes

Global Comparison of Satellite and RadiosondesGlobal Comparison of Satellite and Radiosondes

(Soden and Lanzante 1996)

10(09184)

15(09393)

10(09486)

14(09548)

-12(10384)

Radiosonde – Satellite: Upper Tropospheric Humidity

Temporal Comparisons of Upper Tropospheric Water VaporTemporal Comparisons of Upper Tropospheric Water Vapor

Radiosonde – Satellite: Upper Tropospheric Humidity

Satellites provide a common reference for intercomparing different UTWV measurements and assessing their relative consistency

ARM Water Vapor Intensive Observation PeriodsARM Water Vapor Intensive Observation Periods

Lidar Humidity ProfilesLidar Humidity Profiles::

ARM /CART Raman Lidar ARM /CART Raman Lidar (CARL)(CARL)

GSFC Scanning Raman GSFC Scanning Raman Lidar (SRL)Lidar (SRL)

NASA/LaRC DIAL Lidar NASA/LaRC DIAL Lidar (LASE)(LASE)

Radiosonde Humidity ProfilesRadiosonde Humidity Profiles

Vaisala RS80Vaisala RS80

VIZ Carbon HygristorVIZ Carbon Hygristor

Frostpoint Chilled MirrorFrostpoint Chilled Mirror

RadiancesRadiances

NASA/LaRC Airborne NASA/LaRC Airborne Interferometer (NAST-I)Interferometer (NAST-I)

GOES 6.7 GOES 6.7 m Imager m Imager

The Atmospheric Radiation Measurement (ARM) Program has conducted a series of Water Vapor IOPs over their Central U.S. field site:

1996 WV IOP, 1997 WV IOP, 1999 Lidar IOP, 2000 WV IOP, 2000 AFWEX

ARM Measurement IntercomparisonARM Measurement Intercomparison

ARM Measurement IntercomparisonARM Measurement Intercomparison

Impact of Radiosonde CorrectionsImpact of Radiosonde Corrections

Measurement Intercomparison: RadiosondeMeasurement Intercomparison: Radiosonde

Radiosondes are drier by ~20-30% relative to satellite.

clou

d

clou

d

Measurement Intercomparison: LidarsMeasurement Intercomparison: Lidars

Raman (CARL, SRL) and DIAL (LASE) lidar agree to within ~10%.

clou

d

clou

d

Measurement Intercomparison: NAST-IMeasurement Intercomparison: NAST-I

NAST-I intereferometer and GOES-8 radiances agree to within ~1 K.

Bias SummaryBias Summary

Uncorrected sondes are ~30% drier than GOES in the upper trop (~20% drier than lidar).

Temp-lag corrections can reduce this bias to ~10% wrt lidar.

Lidars, aircraft intereferometer, and satellite agree to ~10%.

Radiosondes Lidars & NAST

Vertical Structure of BiasesVertical Structure of Biases

Direct assimilation of satellite radiances offers potential to greatly improve the radiosonde humidity profiles in the upper troposphere.

SummarySummary

Satellite IR measurements can provide an effective tool for intercomparing upper tropospheric humidity from different instruments.

Vaisala RS80 radiosondes exhibit a systematic dry bias relative to both satellite and lidar measurements.

Existing ARM radiosonde corrections were ineffective in the upper troposphere, however some new corrections show promise (i.e., Miloshevich).

Direct assimilation of satellite radiances offers potential to improve the radiosonde humidity profiles in the upper troposphere when other corrections are not available (e.g., for historical records).

Extra SlidesExtra Slides

Vertical Structure of BiasesVertical Structure of Biases

Existing ARM correction methods improve total column water vapor, but have little impact on the upper troposphere.