Abstract
Routine liquid water path measurements and water vapor path are valuable for process studies of the cloudy marine boundary layer and for the assessment of large-scale models. The VOCALS Regional Experiment respected this goal by including a small, inexpensive, upward-pointing millimeter-wavelength passive radiometer on the fourteen research flights of the NCAR C-130 plane, the G-band (183 GHz) Vapor Radiometer (GVR). The radiometer permitted above-cloud retrievals of the free-tropospheric water vapor path (WVP). Retrieved free-tropospheric (above-cloud) water vapor paths possessed a strong longitudinal gradient, with off-shore values of one to two mm and near-coastal values reaching ten mm. The VOCALS-REx free troposphere was drier than that of previous years. Cloud liquid water paths (LWPs) were retrieved from the sub-cloud and cloudbase aircraft legs through a combination of the GVR, remotely-sensed cloud boundary information, and in-situ thermodynamic data. The absolute (between-leg) and relative (within-leg) accuracy of the LWP retrievals at 1 Hz (∼100 m) resolution was estimated at 20 g m-2 and 3 g m-2 respectively for well-mixed conditions, and 25 g m-2 absolute uncertainty for decoupled conditions where the input WVP specification was more uncertain. Retrieved liquid water paths matched adiabatic values derived from coincident cloud thickness measurements exceedingly well. A significant contribution of the GVR dataset was the extended information on the thin clouds, with 62 % (28 %) of the retrieved LWPs <100 (40) g m -2. Coastal LWPs values were lower than those offshore. For the four dedicated 20 S flights, the mean (median) coastal LWP was 67 (61) g m -2, increasing to 166 (120) g m-2 1500 km offshore. The overall LWP cloud fraction from thirteen research flights was 63 %, higher than that of adiabatic LWPs at 40 %, but lower than the lidar-determined cloud cover of 85 %, further testifying to the frequent occurrence of thin clouds.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 355-369 |
| Number of pages | 15 |
| Journal | Atmospheric Chemistry and Physics |
| Volume | 12 |
| Issue number | 1 |
| DOIs | |
| State | Published - 2012 |
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ASJC Scopus subject areas
- Atmospheric Science
Cite this
Aircraft millimeter-wave passive sensing of cloud liquid water and water vapor during VOCALS-REx. / Zuidema, Paquita; Leon, D.; Pazmany, A.; Cadeddu, M.
In: Atmospheric Chemistry and Physics, Vol. 12, No. 1, 2012, p. 355-369.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Aircraft millimeter-wave passive sensing of cloud liquid water and water vapor during VOCALS-REx
AU - Zuidema, Paquita
AU - Leon, D.
AU - Pazmany, A.
AU - Cadeddu, M.
PY - 2012
Y1 - 2012
N2 - Routine liquid water path measurements and water vapor path are valuable for process studies of the cloudy marine boundary layer and for the assessment of large-scale models. The VOCALS Regional Experiment respected this goal by including a small, inexpensive, upward-pointing millimeter-wavelength passive radiometer on the fourteen research flights of the NCAR C-130 plane, the G-band (183 GHz) Vapor Radiometer (GVR). The radiometer permitted above-cloud retrievals of the free-tropospheric water vapor path (WVP). Retrieved free-tropospheric (above-cloud) water vapor paths possessed a strong longitudinal gradient, with off-shore values of one to two mm and near-coastal values reaching ten mm. The VOCALS-REx free troposphere was drier than that of previous years. Cloud liquid water paths (LWPs) were retrieved from the sub-cloud and cloudbase aircraft legs through a combination of the GVR, remotely-sensed cloud boundary information, and in-situ thermodynamic data. The absolute (between-leg) and relative (within-leg) accuracy of the LWP retrievals at 1 Hz (∼100 m) resolution was estimated at 20 g m-2 and 3 g m-2 respectively for well-mixed conditions, and 25 g m-2 absolute uncertainty for decoupled conditions where the input WVP specification was more uncertain. Retrieved liquid water paths matched adiabatic values derived from coincident cloud thickness measurements exceedingly well. A significant contribution of the GVR dataset was the extended information on the thin clouds, with 62 % (28 %) of the retrieved LWPs <100 (40) g m -2. Coastal LWPs values were lower than those offshore. For the four dedicated 20 S flights, the mean (median) coastal LWP was 67 (61) g m -2, increasing to 166 (120) g m-2 1500 km offshore. The overall LWP cloud fraction from thirteen research flights was 63 %, higher than that of adiabatic LWPs at 40 %, but lower than the lidar-determined cloud cover of 85 %, further testifying to the frequent occurrence of thin clouds.
AB - Routine liquid water path measurements and water vapor path are valuable for process studies of the cloudy marine boundary layer and for the assessment of large-scale models. The VOCALS Regional Experiment respected this goal by including a small, inexpensive, upward-pointing millimeter-wavelength passive radiometer on the fourteen research flights of the NCAR C-130 plane, the G-band (183 GHz) Vapor Radiometer (GVR). The radiometer permitted above-cloud retrievals of the free-tropospheric water vapor path (WVP). Retrieved free-tropospheric (above-cloud) water vapor paths possessed a strong longitudinal gradient, with off-shore values of one to two mm and near-coastal values reaching ten mm. The VOCALS-REx free troposphere was drier than that of previous years. Cloud liquid water paths (LWPs) were retrieved from the sub-cloud and cloudbase aircraft legs through a combination of the GVR, remotely-sensed cloud boundary information, and in-situ thermodynamic data. The absolute (between-leg) and relative (within-leg) accuracy of the LWP retrievals at 1 Hz (∼100 m) resolution was estimated at 20 g m-2 and 3 g m-2 respectively for well-mixed conditions, and 25 g m-2 absolute uncertainty for decoupled conditions where the input WVP specification was more uncertain. Retrieved liquid water paths matched adiabatic values derived from coincident cloud thickness measurements exceedingly well. A significant contribution of the GVR dataset was the extended information on the thin clouds, with 62 % (28 %) of the retrieved LWPs <100 (40) g m -2. Coastal LWPs values were lower than those offshore. For the four dedicated 20 S flights, the mean (median) coastal LWP was 67 (61) g m -2, increasing to 166 (120) g m-2 1500 km offshore. The overall LWP cloud fraction from thirteen research flights was 63 %, higher than that of adiabatic LWPs at 40 %, but lower than the lidar-determined cloud cover of 85 %, further testifying to the frequent occurrence of thin clouds.
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U2 - 10.5194/acp-12-355-2012
DO - 10.5194/acp-12-355-2012
M3 - Article
AN - SCOPUS:84861547683
VL - 12
SP - 355
EP - 369
JO - Atmospheric Chemistry and Physics
JF - Atmospheric Chemistry and Physics
SN - 1680-7316
IS - 1
ER -