AIRS science team meeting Camp Springs, February 2003 Holger Vömel University of Colorado and NOAA/CMDL Upper tropospheric humidity validation measurements

Overview The NOAA/CMDL frost-point hygrometer Sample profile Available data Issues Hygrometer Vaisala Humicap data Snow White Summary

Vertical Range: Lower troposphere to  28 km Sensitivity: Detection limit < 0.7 ppmv Accuracy :  10% The NOAA frost-point hygrometer

Frost-point hygrometer data Frost-point instruments measure frost-point temperature. We use a saturation vapor pressure formulation (Goff Gratch) to calculate vapor pressure, RH, mixing ratio etc. All data shown here are as relative humidity with respect to liquid water.

Sample profile Data files contain: Vaisala P + T Vaisala humicap RH Snow White FP temp NOAA FP temp ECC ozone mr

Available data LocationInstruments# soundings San Cristóbal, GalapagosFP/O3/SW/PTU2 San Cristóbal, GalapagosPTU19 San Cristóbal, Galapagos * O3/PTU4 Hilo, HIFP/O3/SW/PTU7 Huntsville, AL ** FP/O3/SW/PTU2 Boulder, COFP/O3/SW/PTU1 Sodankylä, Finland *** FP/O3/SW/PTU2 *) SHADOZ data **) Simultaneous BBAERI observations ***) SAGE III validation sounding All data are located at: /dom/files/ops/correl/point/YYYY/MM/val_voem/

Data issues: NOAA Hygrometer Filtered data gaps : Gain change Mid level clear Frost-point controller not optimized for lower troposphere  oscillations

Data issues: NOAA Hygrometer Hygrometer data files contain ascent and descent data. Time stamp tells, whether the data are ascent or descent. In some cases there are significant real differences between the ascent location and the descent location.

Data issues: Vaisala humicap Vaisala UTH issues: Two Humicap types: Humicap-H: Most common type Humicap-A: Old sensor (military still uses it) Time lag! Important at T < -40 °C Contamination of the sensor. Important issue for sondes manufactured before New sensor protective cap introduced in 2001 improves this potential source of error. Dry bias (for humicap type-A). Only few of these sondes are sold Not an issue for AIRS validation measurements.

The Meteolabor Snow White sonde Vertical Range: Lower troposphere to upper troposphere Accuracy:  0.1°C (company spec.)

Data issues: Snow White low RH limit Snow White may loose frost- coverage on the mirror  Loss of frost-point control May affect the entire profile

Data issues: Snow White low RH limit Snow White may loose frost- coverage on the mirror  Loss of frost-point control May affect the entire profile or shallow layers after the dry layer RH min ≥ 5-8 %

Data issues: Dew vs. ice ambiguity Humidity differences at low altitudes

Data issues: Dew vs. ice ambiguity Humidity differences at low altitudes Due to the ambiguity of ice or dew coverage of the mirror Need to use different vapor pressure curve

Snow White upper tropospheric limit Upper tropospheric limit depends on frost-point temperature At T FP < -75°C the Snow White does no longer measure reliably

NOAA/CMDL frost-point hygrometer measures accurately up to the middle stratosphere Few data gaps due to oscillations, mirror clear, gain change Vaisala humicap sensor Assume only Vaisala Humicap-H is used Time lag is an important issue in the upper troposphere (T < -40°C) Contamination probably not a serious issue for newer sondes (new cap) Snow White Has a lower limit of 5-8% RH Ambiguity of ice/dew T > -25°C Limit to tropospheric measurements with T FP > -75°C All data files have a field that contains the ‘Best MR’, which combines the best data from the three sensors into one field. Summary

NOAA/CMDL/MLO AIRS Validation Three examples of water vapor observations, integration time 2 hours for Upper Trop, cirrus measured with lidar aerosol channels at 532 and 1064 nm.

NOAA/CMDL/Mauna Loa Observatory Validation of AIRS for First Year ProposedActual Water Vapor Raman Lidar1417 Radiosonde77 Frost-Point5 for lidar calibration2 for lidar calibration 3 for AIRS Validation Temperature CMDL Radiosonde77 Ozone Ozonesonde77 Temperature note: The NWS releases daily radiosondes at 2:00 AM and PM local time which measure accurate temperature profiles.

PWV and Cloud Conditions

SnowWhite - NOAA comparisons: Dry limit

Data issues: Humicap-A dry bias

SnowWhite - NOAA comparisons: Dry limit