# Presentation: 095271

## AIRS science team meetingCamp Springs, 25-27 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

## The NOAA frost-point hygrometer 

- 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

| Location | Instruments | # soundings |
| --- | --- | --- |
| San Cristóbal, Galapagos | FP/O3/SW/PTU | 2 |
| San Cristóbal, Galapagos | PTU | 19 |
| San Cristóbal, Galapagos* | O3/PTU | 4 |
| Hilo, HI  | FP/O3/SW/PTU | 7 |
| Huntsville, AL ** | FP/O3/SW/PTU | 2 |
| Boulder, CO  | FP/O3/SW/PTU | 1 |
| Sodankylä, Finland*** | FP/O3/SW/PTU | 2 |

- *) 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 2002. 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 TFP < -75°C the Snow White does no longer measure reliably

## Summary

-  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 TFP > -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

|  | Proposed | Actual |
| --- | --- | --- |
| Water Vapor |  |  |
| Raman Lidar | 14 | 17 |
| Radiosonde | 7 | 7 |
| Frost-Point | 5 for lidar calibration | 2 for lidar calibration
3 for AIRS Validation |
| Temperature |  |  |
| CMDL Radiosonde | 7 | 7 |
| Ozone |  |  |
| Ozonesonde | 7 | 7 |

- 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

*SnowWhite - NOAA comparisons:**Dry limit*

## SnowWhite - NOAA comparisons:Dry limit

*SnowWhite - NOAA comparisons:**Dry limit*

## Data issues: Humicap-A dry bias

## SnowWhite - NOAA comparisons:Dry limit