Water vapor variability and comparisons in the subtropical Pacific from the Observing System Research and Predictability Experiment-Pacific Asian Regional Campaign (T-PARC) Driftsonde, Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC), and reanalyses
Journal
Journal of Geophysical Research Atmospheres
Journal Volume
115
Journal Issue
21
Date Issued
2010
Author(s)
Wang, J. et al.
Zhang, L.
Bradford, M.
Cole, H.
Fox, J.
Hock, T.
Lauritsen, D.
Loehrer, S.
Martin, C.
Vanandel, J.
Weng, C.-H.
Young, K.
Abstract
During the THORPEX (The Observing System Research and Predictability Experiment) Pacific Asian Regional Campaign (T-PARC), from 1 August to 30 September 2008, ~1900 high-quality, high vertical resolution soundings were collected over the Pacific Ocean. These include dropsondes deployed from four aircrafts and zero-pressure balloons in the stratosphere (NCAR's Driftsonde system). The water vapor probability distribution and spatial variability in the northern subtropical Pacific (14°-20°N, 140°E-155°W) are studied using Driftsonde and COSMIC (Constellation Observing System forMeteorology, Ionosphere, and Climate) data and four global reanalysis products. Driftsonde data analysis shows distinct differences of relative humidity (RH) distributions in the free troposphere between the Eastern and Western Pacific (EP and WP, defined as east and west of 180°, respectively), very dry with a single peak of ~1% RH in the EP and bi-modal distributions in the WP with one peak near ice saturation and one varying with altitude. The frequent occurrences of extreme dry air are found in the driftsonde data with 59% and 19% of RHs less than or equal to 5% and at 1% at 500 hPa in the EP, respectively. RH with respect to ice in the free troposphere exhibits considerable longitudinal variations, very low (<20%) in the EP, but varying from 20% to 100% in theWP. Inter-comparisons of Driftsonde, COSMIC and reanalysis data show generally good agreement among the Driftsonde, COSMIC, ECMWF Reanalysis-Interim (ERA-Interim) and Japanese Reanalysis (JRA) below 200 hPa. The ERA-Interim and JRA are approved to be successful on describing RH frequency distributions and spatial variations in the region. The comparisons also reveal problems in Driftsonde, two National Center for Environmental Prediction (NCEP) reanalyses and COSMIC data. The moist layer at 200-100 hPa in the WP shown in the ERA-Interim, JRA and COSMIC is missing in Driftsonde data. Major problems are found in the RH means and variability over the study region for both NCEP reanalyses. Although the higher-moisture layer at 200-100 hPa in theWP in the COSMIC data agrees well with the ERA-Interim and JRA, it is primarily attributed to the first guess of the 1-Dimensional (1D) variational analysis used in the COSMIC retrieval rather than the refractivity measurements. The limited soundings (total 268) of Driftsonde data are capable of portraying RHprobability distributions and longitudinal variability. This implies that Driftsonde system has the potential to become a valuable operational system for upper air observations over the ocean. Copyright © 2010 by the American Geophysical Union.
SDGs
Other Subjects
Atmospheric humidity; Atmospherics; Data reduction; Experiments; Ionosphere; Ionospheric measurement; Probability distributions; Rhodium compounds; Troposphere; Water vapor; Weather satellites; Bimodal distribution; Constellation observing system for meteorology , ionosphere , and climates; Data analysis; Dry air; Ecmwf re-analysis; Free troposphere; Frequency distributions; High quality; High vertical resolution; Longitudinal variations; National center for environmental predictions; Observing systems; Operational systems; Pacific ocean; Reanalysis; Refractivity measurements; Relative humidities; Single peak; Spatial variability; Spatial variations; Upper air; Variational analysis; Western Pacific; Cosmology; aircraft; one-dimensional modeling; pressure effect; probability; relative humidity; spatial resolution; stratosphere-troposphere interaction; water vapor; Pacific Ocean
Type
journal article