Harold L. Cole

Corrections of Humidity Measurement Errors from the Vaisala RS80 Radiosonde—Application to TOGA COARE Data

A series of laboratory tests have been conducted on several different batches of Vaisala RS80 radiosondes to understand and develop methods to correct six humidity measurement errors, including chemical contamination, temperature dependence, basic calibration model, ground check, sensor aging, and sensor arm heating. The contamination and temperature-dependence (TD) errors dominate total errors. The chemical contamination error produces a dry bias, and is due to the occupation of binding sites in the sensor polymer by nonwater molecules emitted from the sonde packaging material. The magnitude of the dry bias depends on sensor polymer type (RS80-A and RS80H), age of the sonde, relative humidity (RH), and temperature, and it exists throughout the troposphere. The contamination error generally increases with age and RH, and is larger for the RS80-H than the RS80-A. It is ;2% and ;10% at saturation for 1-yr-old RS80-A and RS80-H sondes, respectively. The TD error for the RS80-A results from an approximation of a linear function of temperature to the actual nonlinear temperature dependence of the sensor, and also introduces a dry bias. The TD error mainly exists at temperatures below 2208C, increases substantially with decreasing temperatures below 2308C, and is much larger for the RS80-A than the RS80-H. The RS80-A’s TD correction (CTA) dominates the total correction at temperatures below 2408C and has a correction factor [CTA 5 (RH) (CTApfactor)] of 0.15, 0.75, and 2.3 at 2408, 2608, and 2808C, respectively. The correction methods are applied to 8129 Vaisala RS80 soundings collected during the Tropical Ocean and Global Atmosphere (TOGA) Coupled Ocean‐Atmosphere Response Experiment (COARE) and are applicable to RS80 radiosonde data from other field experiments and historical and operational radiosonde datasets. The methods are validated by examining various summary plots of the TOGA COARE data and comparing them with other independent data. The corrections greatly improve the accuracy of the TOGA COARE radiosonde dataset. These correction methods have their own uncertainties and may not correct all errors in Vaisala RS80 humidity data. Analyses of these uncertainties are presented in the paper.

The Integrated Sounding System: Description and Preliminary Observations from TOGA COARE

Abstract An Integrated Sounding System (ISS) that combines state-of- the-art remote and in situ sensors into a single transportable facility has been developed jointly by the National Center for Atmospheric Research (NCAR) and the Aeronomy laboratory of the National Oceanic and Atmospheric Administration (NOAA/AL). The instrumentation for each ISS includes a 915-MHz wind profiler, a Radio Acoustic Sounding System (RASS), an Omega-based NAVAID sounding system, and an enhanced surface meteorological station. The general philosophy behind the ISS is that the integration of various measurement systems overcomes each systems respective limitations while taking advantage of its positive attributes. The individual observing systems within the ISS provide high-level data products to a central workstation that manages and integrates these measurements. The ISS software package performs a wide range of functions: real-time data acquisition, database support, and graphical displays; data archival and communications...

Performance of operational radiosonde humidity sensors in direct comparison with a chilled mirror dew‐point hygrometer and its climate implication

[1]xa0This study evaluates performance of humidity sensors in two widely used operational radiosondes, Vaisala and Sippican (formally VIZ), in comparison with a research quality, and potentially more accurate, chilled mirror dew-point hygrometer named “Snow White”. A research radiosonde system carrying the Snow White (SW) hygrometer was deployed in the Oklahoma panhandle and at Dodge City, KS during the International H2O Project (IHOP_2002). A total of sixteen sondes were launched with either Vaisala RS80 or Sippican VIZ-B2 radiosondes on the same balloons. Comparisons of humidity data from the SW with Vaisala and Sippican data show that (a) Vaisala RS80-H agrees with the SW very well in the middle and lower troposphere, but has dry biases in the upper troposphere (UT), (b) Sippican carbon hygristor (CH) has time-lag errors throughout the troposphere and fails to respond to humidity changes in the UT, sometimes even in the middle troposphere, and (c) the SW can detect cirrus clouds near the tropopause and possibly estimate their ice water content (IWC). The failure of CH in the UT results in significant and artificial humidity shifts in radiosonde climate records at stations where a transition from VIZ to Vaisala radiosondes has occurred.

Vertical Air Motion from T-REX Radiosonde and Dropsonde Data

Abstract The primary goal of this study is to explore the potential for estimating the vertical velocity (VV) of air from the surface to the stratosphere, using widely available radiosonde and dropsonde data. The rise and fall rates of radiosondes and dropsondes, respectively, are a combination of the VV of the atmosphere and still-air rise–fall rates. The still-air rise–fall rates are calculated using basic fluid dynamics and characteristics of radiosonde and dropsonde systems. This study validates the technique to derive the VV from radiosonde and dropsonde data and demonstrates its value. This technique can be easily implemented by other users for various scientific applications. The technique has been applied to the Terrain-induced Rotor Experiment (T-REX) dropsonde and radiosonde data. Comparisons among radiosonde, dropsonde, aircraft, and profiling radar vertical velocities show that the sonde-estimated VV is able to capture and describe events with strong vertical motions (larger than ∼1 m s−1) obs...

First Test of a Shipboard Wind Profiler

Abstract The Aeronomy Laboratory of the National Oceanic and Atmospheric Administration and the Atmospheric Technology Division of the National Center for Atmospheric Research are jointly developing Integrated Sounding Systems (ISS) for use in support of TOGA (Tropical Ocean Global Atmosphere) and TOGA COARE (Coupled Ocean-Atmosphere Response Experiment). Some of the ISS units will have to be operated on research ships during TOGA COAREs intensive observing period in late 1992 and early 1993. The greatest technical challenge in adapting the ISS to shipboard use is to stabilize the UHF wind profiler that is an integral part of the ISS. In June 1991 a UHF wind-profiling Doppler radar was installed on a stabilized platform aboard the NOAA research vessel Malcolm Baldrige on an eight-day cruise in the Atlantic Ocean. The wind profiler was gyrostabilized and profiler winds were corrected for ship motion utilizing the Global Positioning System. During the eight days at sea, CLASS (Cross-Chain LORAN Atmospheric...

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

[1]xa0During 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 (NCARs 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 for Meteorology, 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 the WP. 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 the WP 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 RH probability 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.

Targeted Dropwindsondes in Complex Terrain

Abstract The dropwindsonde (or dropsonde) is a frequently utilized tool in geophysical research and its use over ocean and flat terrain is a reliable and well-established practice. Its use in complex terrain, however, is complicated by signal acquisition challenges that can be directly related to the ground target location, local relief, and line of sight to flight tracks relevant to the observation sought. This note describes a straightforward technique to calculate the theoretical altitude above ground to which a ground-targeted dropsonde will provide data for a given airborne platform. It is found that this height HCq can be calculated from expected airborne platform horizontal velocity Uag, mean dropwindsonde vertical velocity Ws, the relevant barrier maximum HB, and the horizontal distance from the target area to the barrier maximum DB. Here, HCq is found to be weakly dependent on release altitude through Ws. An example from the Terrain-induced Rotor Experiment (T-REX) is used to show that for modern...

A reference radiosonde system for climate and weather research: IHOP experience

Global radiosonde data are required by meteorological analysis centers for initializing numerical prediction models for weather forecasting, and represent an increasingly valuable resource for studies of climate change and in the development, calibration and validation of retrieval techniques for atmospheric temperature and water vapor profiles from satellite. Unfortunately, the usefulness of radiosonde data is limited by sensor accuracy, by data reporting practices, and by the fact that sonde and sensor types vary by location and with time. Numerous studies and reports have called for a reference sonde to serve as a transfer standard to compare and connect data from past, present and future sonde systems. We are working on developing a reference radiosonde system at the Atmospheric Technology Division (ATD) at NCAR. The reference radiosonde system will carry the best sensors, have a flexible infrastructure to host multiple and different user-provided sensors and will be recoverable to reduce costs. The first version of the reference radiosonde system was deployed in the Oklahoma panhandle and Dodge City, KS (NWS radiosonde site) during the International H2O Project (IHOP_2002). A total of sixteen reference sondes were launched during IHOP either with Vaisala RS80 or Sippican (VIZ) radiosondes. The humidity data from the reference humidity sensor (Snow White, SW) are compared with Vaisala and VIZ data. The comparisons show that (a) VIZ carbon hygristor fails to respond to humidity changes in the upper troposphere, (b) the carbon hygristor inside the reference sonde has slower response than that inside NWS VIZ sonde, (c) Vaisala RS80-H agrees with SW very well in the middle and lower troposphere, and (d) SW can detect cirrus clouds near the tropopause and possibly estimate their ice water content (IWC). The climate impacts of these results are also discussed.