Lower-tropospheric Moisture Research Articles

A Simple Multicloud Parameterization for Convectively Coupled Tropical Waves. Part II: Nonlinear Simulations

Abstract Observations in the Tropics point to the important role of three cloud types, congestus, stratiform, and deep convective clouds, besides ubiquitous shallow boundary layer clouds for both the climatology and large-scale organized anomalies such as convectively coupled Kelvin waves, two-day waves, and the Madden–Julian oscillation. Recently, the authors have developed a systematic model convective parameterization highlighting the dynamic role of the three cloud types through two baroclinic modes of vertical structure: a deep convective heating mode and a second mode with lower troposphere heating and cooling corresponding respectively to congestus and stratiform clouds. The model includes both a systematic moisture equation where the lower troposphere moisture increases through detrainment of shallow cumulus clouds, evaporation of stratiform rain, and moisture convergence and decreases through deep convective precipitation and also a nonlinear switch that favors either deep or congestus convection depending on whether the lower middle troposphere is moist or dry. Here these model convective parameterizations are applied to a 40 000-km periodic equatorial ring without rotation, with a background sea surface temperature (SST) gradient and realistic radiative cooling mimicking a tropical warm pool. Both the emerging “Walker cell” climatology and the convectively coupled wave fluctuations are analyzed here while various parameters in the model are varied. The model exhibits weak congestus moisture coupled waves outside the warm pool in a turbulent bath that intermittently amplify in the warm pool generating convectively coupled moist gravity wave trains propagating at speeds ranging from 15 to 20 m s−1 over the warm pool, while retaining a classical Walker cell in the mean climatology. The envelope of the deep convective events in these convectively coupled wave trains often exhibits large-scale organization with a slower propagation speed of 3–5 m s−1 over the warm pool and adjacent region. Occasional much rarer intermittent deep convection also occurs outside the warm pool. The realistic parameter regimes in the multicloud model are identified as those with linearized growth rates for large scale instabilities roughly in the range of 0.5 K day−1.

Transition between Suppressed and Active Phases of Intraseasonal Oscillations in the Indo-Pacific Warm Pool

Abstract Intraseasonal oscillations (ISOs) are important large-amplitude and large-scale elements of the tropical Indo-Pacific climate with time scales in the 20–60-day period range, during which time they modulate higher-frequency tropical weather. Despite their importance, the ISO is poorly simulated and predicted by numerical models. A joint diagnostic and modeling study of the ISO is conducted, concentrating on the period between the suppressed and active (referred to as the “transition”) period that is hypothesized to be the defining stage for the development of the intraseasonal mode and the component that is most poorly simulated. The diagnostic study uses data from the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). It is found that during the transition period, the ocean and the atmosphere undergo gradual but large-scale and high-amplitude changes, especially the moistening of the lower troposphere caused jointly by the anomalously warm sea surface temperature arising from minimal cloud and low winds during the suppressed phase and the large-scale subsidence that inhibits the formation of locally deep convection. Using a cloud classification scheme based on microwave and infrared satellite data, it is observed that midtop (cloud with a top in the middle troposphere) nonprecipitating clouds are a direct response of the low-level moisture buildup. To investigate the sensitivity of ISO simulations to the transitional phase, the European Centre for Medium-Range Weather Forecasts (ECMWF) coupled ocean–atmosphere climate model is used. The ECMWF was run serially in predictive ensemble mode (five members) for 30-day periods starting from 1 December 1992 to 30 January 1993, encompassing the ISO occurring in late December. Predictability of the active convective period of the ISO is poor when initialized before the transitional phases of the ISO. However, when initialized with the correct lower-tropospheric moisture field, predictability increases substantially, although the model convective parameterization appears to trigger convection too quickly without allowing an adequate buildup of convective available potential energy during the transition period.

Vertical Moist Thermodynamic Structure and Spatial–Temporal Evolution of the MJO in AIRS Observations

Abstract The atmospheric moisture and temperature profiles from the Atmospheric Infrared Sounder (AIRS)/Advanced Microwave Sounding Unit on the NASA Aqua mission, in combination with the precipitation from the Tropical Rainfall Measuring Mission (TRMM), are employed to study the vertical moist thermodynamic structure and spatial–temporal evolution of the Madden–Julian oscillation (MJO). The AIRS data indicate that, in the Indian Ocean and western Pacific, the temperature anomaly exhibits a trimodal vertical structure: a warm (cold) anomaly in the free troposphere (800–250 hPa) and a cold (warm) anomaly near the tropopause (above 250 hPa) and in the lower troposphere (below 800 hPa) associated with enhanced (suppressed) convection. The AIRS moisture anomaly also shows markedly different vertical structures as a function of longitude and the strength of convection anomaly. Most significantly, the AIRS data demonstrate that, over the Indian Ocean and western Pacific, the enhanced (suppressed) convection is generally preceded in both time and space by a low-level warm and moist (cold and dry) anomaly and followed by a low-level cold and dry (warm and moist) anomaly. The MJO vertical moist thermodynamic structure from the AIRS data is in general agreement, particularly in the free troposphere, with previous studies based on global reanalysis and limited radiosonde data. However, major differences in the lower-troposphere moisture and temperature structure between the AIRS observations and the NCEP reanalysis are found over the Indian and Pacific Oceans, where there are very few conventional data to constrain the reanalysis. Specifically, the anomalous lower-troposphere temperature structure is much less well defined in NCEP than in AIRS for the western Pacific, and even has the opposite sign anomalies compared to AIRS relative to the wet/dry phase of the MJO in the Indian Ocean. Moreover, there are well-defined eastward-tilting variations of moisture with height in AIRS over the central and eastern Pacific that are less well defined, and in some cases absent, in NCEP. In addition, the correlation between MJO-related midtropospheric water vapor anomalies and TRMM precipitation anomalies is considerably more robust in AIRS than in NCEP, especially over the Indian Ocean. Overall, the AIRS results are quite consistent with those predicted by the frictional Kelvin–Rossby wave/conditional instability of the second kind (CISK) theory for the MJO.

Model multi-cloud parameterizations for convectively coupled waves: Detailed nonlinear wave evolution

Recent observational analysis reveals the central role of three cloud types, congestus, stratiform, and deep-convective cumulus clouds, in the dynamics of large scale convectively coupled Kelvin waves, westward propagating 2-day waves, and the Madden–Julian oscillation. Recently, a systematic model convective parametrization highlighting the dynamic role of the three cloud types has been developed by the authors involving two baroclinic modes of vertical structure: a deep-convective heating mode and a second mode with low level heating and cooling corresponding, respectively, to congestus and stratiform clouds. The model includes a systematic moisture equation where the lower troposphere moisture increases through detrainment of shallow cumulus clouds, evaporation of stratiform rain, and moisture convergence and decreases through deep-convective precipitation and also a nonlinear switch which favors either deep or congestus convection depending on the relative dryness of the middle troposphere. The detailed nonlinear evolution of large scale convectively coupled waves in the model parametrization is studied here in a chaotic intermittent regime of the nonlinear dynamics associated with weaker mean radiative cooling where such waves are isolated in space and time. This regime is utilized to elucidate in a clean fashion several novel features of the model parametrization. In particular, four stages of nonlinear wave evolution occur: in the preconditioning and birth stages, the role of congestus moistening and second baroclinic convergence are crucial while in the dying stage of the large scale convectively coupled wave, the role of the nonlinear switch, and the drying of the troposphere are essential. In the mature phase, the large scale features of the convectively coupled waves resemble those in observations of convectively coupled Kelvin waves including the propagation speed, wave tilt, temperature, heating, and velocity structure.

Multicloud Convective Parametrizations with Crude Vertical Structure

Recent observational analysis reveals the central role of three multi-cloud types, congestus, stratiform, and deep convective cumulus clouds, in the dynamics of large scale convectively coupled Kelvin waves, westward propagating two-day waves, and the Madden–Julian oscillation. The authors have recently developed a systematic model convective parametrization highlighting the dynamic role of the three cloud types through two baroclinic modes of vertical structure: a deep convective heating mode and a second mode with low level heating and cooling corresponding respectively to congestus and stratiform clouds. The model includes a systematic moisture equation where the lower troposphere moisture increases through detrainment of shallow cumulus clouds, evaporation of stratiform rain, and moisture convergence and decreases through deep convective precipitation and a nonlinear switch which favors either deep or congestus convection depending on whether the troposphere is moist or dry. Here several new facets of these multi-cloud models are discussed including all the relevant time scales in the models and the links with simpler parametrizations involving only a single baroclinic mode in various limiting regimes. One of the new phenomena in the multi-cloud models is the existence of suitable unstable radiative convective equilibria (RCE) involving a larger fraction of congestus clouds and a smaller fraction of deep convective clouds. Novel aspects of the linear and nonlinear stability of such unstable RCE’s are studied here. They include new modes of linear instability including mesoscale second baroclinic moist gravity waves, slow moving mesoscale modes resembling squall lines, and large scale standing modes. The nonlinear instability of unstable RCE’s to homogeneous perturbations is studied with three different types of nonlinear dynamics occurring which involve adjustment to a steady deep convective RCE, periodic oscillation, and even heteroclinic chaos in suitable parameter regimes.

A Simple Multicloud Parameterization for Convectively Coupled Tropical Waves. Part I: Linear Analysis

AbstractRecent observational analysis reveals the central role of three multicloud types, congestus, stratiform, and deep convective cumulus clouds, in the dynamics of large-scale convectively coupled Kelvin waves, westward-propagating two-day waves, and the Madden–Julian oscillation. A systematic model convective parameterization highlighting the dynamic role of the three cloud types is developed here through two baroclinic modes of vertical structure: a deep convective heating mode and a second mode with low-level heating and cooling corresponding respectively to congestus and stratiform clouds. A systematic moisture equation is developed where the lower troposphere moisture increases through detrainment of shallow cumulus clouds, evaporation of stratiform rain, and moisture convergence and decreases through deep convective precipitation. A nonlinear switch is developed that favors either deep or congestus convection depending on the relative dryness of the troposphere; in particular, a dry troposphere with large convective available potential energy (CAPE) has no deep convection and only congestus clouds. The properties of the multicloud model parameterization are tested by linearized analysis in a two-dimensional setup with no rotation with constant sea surface temperature. In particular, the present study reveals new mechanisms for the large-scale instability of moist gravity waves with features resembling observed convectively coupled Kelvin waves in realistic parameter regimes without any effect of wind-induced surface heat exchange (WISHE). A detailed dynamical analysis for the linear waves is given herein and idealized nonlinear numerical simulations are reported in a companion paper. A maximum congestus heating leads during the dry phase of the wave. It is followed by an increase of the boundary layer θe, that is, CAPE, and lower troposphere moistening that precondition the upper troposphere for the next deep convective episode. In turn, deep convection consumes CAPE and removes moisture, thus yielding the dry episode.

Analyses of hot and humid weather in Beijing city in summer and its dynamical identification

The circulation, hygrothermal property and moisture transport character of typical hot and humid weather were analyzed in Beijing areas from July 30 to August 4, 2002. It was pointed out that, under the control of subtropical anticyclone which stretches to the west and north, downdraft suppresses the lifting of lower-troposphere moisture, which makes moisture keep in the lower troposphere. That is the direct reason causing hot and humid weather. Considering the non-uniformity saturated character in real atmosphere, generalized moist potential vorticity (GMPV) equation is derived by the introduction of generalized moist potential temperature concept. The analysis of GMPV shows that negative GMPV anomaly occurs in the lower troposphere. It has indicative sense to hot and humid weather. Thus, the GMPV anomaly can be utilized to identify this kind of weather and to make a short-term prediction.

The Rainfall Phenomena during the Pre-monsoon Period over the Indochina Peninsula in the GAME-IOP Year, 1998

The rainfall phenomena in the pre-monsoon season over the Indochina Peninsula are investigated using geopotential height, wind and moisture fields by the NCEP/NCAR reanalysis, and OLR, precipitation and GPS data during the GAME-IOP year, 1998. In early and middle April, and early May, the lower OLR regions, which represent the heavy convective activity, extend southward from the mid-latitude zone to the Indochina Peninsula, bringing intermittent rainfall events in a wide region over the central part ofthe peninsula. The composite analysis in these three rainfall events shows that they are brought by the trough passage in the upper troposphere, which migrates eastward in the middlel atitude westerlies along the southern periphery of the Tibetan Plateau. The lower tropospheric moisture inflow in these rainfall events is found to come mainly from the south and east, which shows sharp contast with the situations of inflow mainly from the west, during the non-precipitation days in the premonsoon season, and the rainfall situations after the monsoon onset in middle May.

Interannual variability of lower‐tropospheric moisture transport during the Australian monsoon

AbstractThe interannual variability of the horizontal lower‐tropospheric moisture transport associated with the Australian summer monsoon has been analysed for the 1958–99 period. The 41‐season climatology of moisture flux integrated between the surface and 450 hPa showed moderate levels of westerly transport in the month before Australian monsoon onset, associated with cross‐equatorial flow in the Sulawesi Sea and west of Borneo. In the month after onset the westerly moisture transport strengthened dramatically in a zonal belt stretching from the Timor Sea to the Western Equatorial Pacific, constrained between the latitudes 5 and 15 °S, and associated with a poleward shift in the Intertropical Convergence Zone and deepening of the monsoon trough. Vertical cross‐sections showed this transport extending from the surface to the 500 hPa level. In the second and third months after onset the horizontal flow pattern remained similar, although flux magnitudes progressively decreased, and the influence of trade winds became more pronounced over northern Australia.Nine El Niño and six La Niña seasons were identified from the data set, and composite plots of the affected years revealed distinct, and in some cases surprising, alterations to the large‐scale moisture transport in the tropical Australian–Indonesian region. During an El Niño it was shown that the month prior to onset, in which the moisture flux was weaker than average, yielded to a dramatically stronger than average flux during the following month, with a zone of westerly flux anomalies stretching across the north Australian coast and Arafura Sea. The period of enhanced moisture flux during an El Niño is relatively short‐lived, with drier easterly anomalies asserting themselves during the following 2 months, suggesting a shorter than usual monsoon period in north Australia. In the La Niña composite, the initial month after onset shows a tendency to weaker horizontal moisture transport over the Northern Territory and Western Australia. The subsequent 2 months show positive anomalies in flux magnitude over these areas; the overall effect is to prolong the monsoon.Comparison of these results with past research has led us to suggest that the tendency for stronger (weaker) circulations to arise in the initial month of El Niño (La Niña) events is a result of mesoscale changes in soil moisture anomalies on land and offshore sea surface temperature (SST) anomalies, brought about by the large‐scale alterations to SST and circulation patterns during the El Niño–Southern Oscillation. The soil moisture and SST anomalies initially act to enhance (suppress) the conditions necessary for deep convection in the El Niño (La Niña) cases via changes in land–sea thermal contrast and cloud cover. Copyright © 2002 Royal Meteorological Society.

Some Meteorological Characteristics of Significant Tornado Events Occurring in Proximity to Flash Flooding

A study was performed to determine meteorological aspects of environments in which thunderstorms produced both strong or violent tornadoes and flash floods within a limited temporal and spatial domain. It was found that the overwhelming majority of these episodes occurred in the spring and summer months and during the afternoon and evening hours. In most instances, at least some of the tornadoes were present when flash flooding was in progress. The ambient environment usually included an air mass that exhibited both relatively high convective instability and abundant lower-tropospheric moisture, including an average most-unstable CAPE of 3200 J kg−1 and mean surface dewpoint and precipitable water values of 70°F (21°C) and 41 mm (1.6 in.), respectively. Storm-relative helicity magnitudes indicated that the vertical wind shear ranged from marginally to moderately favorable for supercell formation in all cases. Surface patterns for each episode were generally similar to patterns earlier studies determined to be frequently attendant with flash flooding, in which preexisting surface boundaries acted to focus deep convection. Most events also occurred east of an approaching and well-defined upper-tropospheric trough and in the left-front or right-rear quadrant of an upper-level jet streak in which upward vertical motion is usually present.

A method for assessing the quality of model‐based estimates of ground temperature and atmospheric moisture using satellite data

A method is developed for validating model‐based estimates of atmospheric moisture and ground temperature using satellite data. The approach relates errors in estimates of clear‐sky longwave fluxes at the top of the Earth‐atmosphere system to errors in geophysical parameters. The fluxes include clear‐sky outgoing longwave radiation (CLR) and radiative flux in the window region between 8 and 12 μm (RadWn). The approach capitalizes on the availability of satellite estimates of CLR and RadWn and other auxiliary satellite data, and multiple global four‐dimensional data assimilation (4‐DDA) products. The basic methodology employs off‐line forward radiative transfer calculations to generate synthetic clear‐sky longwave fluxes from two different 4‐DDA data sets. Simple linear regression is used to relate the clear‐sky longwave flux discrepancies to discrepancies in ground temperature (δTg) and broad‐layer integrated atmospheric precipitable water (δpw). The slopes of the regression lines define sensitivity parameters which can be exploited to help interpret mismatches between satellite observations and model‐based estimates of clear‐sky longwave fluxes. For illustration we analyze the discrepancies in the clear‐sky longwave fluxes between an early implementation of the Goddard Earth Observing System Data Assimilation System (GEOS2) and a recent operational version of the European Centre for Medium‐Range Weather Forecasts data assimilation system. The analysis of the synthetic clear‐sky flux data shows that simple linear regression employing δTg and broad layer δpw provides a good approximation to the full radiative transfer calculations, typically explaining more than 90% of the 6 hourly variance in the flux differences. These simple regression relations can be inverted to “retrieve” the errors in the geophysical parameters. Uncertainties (normalized by standard deviation) in the monthly mean retrieved parameters range from 7% for δTg to ∼20% for the lower tropospheric moisture between 500 hPa and surface. The regression relationships developed from the synthetic flux data, together with CLR and RadWn observed with the Clouds and Earth Radiant Energy System instrument, are used to assess the quality of the GEOS2 Tg and pw. Results showed that the GEOS2 Tg is too cold over land, and pw in upper layers is too high over the tropical oceans and too low in the lower atmosphere.

Multiscale Overview of a Violent Tornado Outbreak with Attendant Flash Flooding

On 1 March 1997 violent tornadoes caused numerous fatalities and widespread damage across portions of central and eastern Arkansas and western Tennessee. In addition, the associated thunderstorms produced very heavy rainfall and flash flooding, with a few locations receiving up to 150 mm (6 in.) of rainfall in 3 h. The initial environment appeared favorable for strong tornadoes with unseasonably warm moist air at lower levels resulting in significant instability (convective available potential energy values between 1400 and 1800 J kg−1) where 0–2-km storm-relative helicities exceeded 300 m2 s−2 and the middle-tropospheric storm-relative flow was conducive for tornadic supercells. The most destructive tornadoes developed along a preexisting surface boundary where lower-tropospheric moisture convergence and frontogenesis were enhanced. Tornadoes and heaviest rainfall only ensue after upward motion associated with the direct circulation of an upper-tropospheric jet streak became collocated with lower-tropospheric upward forcing along the surface boundaries. From a flash flood perspective the event occurred in a hybrid mesohigh-synoptic heavy rain pattern as thunderstorms developed and moved along surface boundaries aligned nearly parallel to the mean wind. In addition, strong flow and associated moisture flux convergence in the lower troposphere favored the formation of cells to the southwest or upstream of the initial convection with thunderstorms, including a a tornadic supercell, traversing over the same area. The available moisture and ambient instability also supported both vigorous updrafts and high precipitation rates.

Observation of a Quasi-2-Day Wave during TOGA COARE

Detailed structure of the quasi-2-day oscillation observed in the active phase of the Madden–Julian oscillations during the intensive observation period of Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE IOP) was described. A variety of observational platforms is used including high-resolution GMS infrared histogram, rain-rate estimate from TOGA and MIT radar measurements, upper-air soundings, and boundary layer profiler winds from the Integrated Sounding System and surface data from the IMET buoy. The quasi-2-day mode had a westward propagation speed of 12°–15° day −1, a horizontal wavelength of 25°–30° longitude. A coupling with the westward-propagating n = 1 inertio–gravity waves was hypothesized from the space–time power spectral distribution of the cloud field. The wind disturbance structure was consistent with the hypothesis. The vertical wave structure had an eastward phase tilt with height below 175 hPa and vice versa above, indicating the wave energy emanating from the upper troposphere. Four stages in the life cycle of the oscillating cloud–circulation system were identified:. 1) the shallow convection stage with a duration time of 12 h, 2) the initial tower stage (9 h), 3) the mature stage (12 h), and 4) the decaying stage (15 h). Surface and boundary layer observations also showed substantial variation associated with the different stages in the life cycle. Results suggest that the timescale of quasi-2-day oscillation is determined by the time required by the lower-tropospheric moisture field to recover from the drying caused by deep convection.

A Satellite Analysis of Deep Convection, Upper-Tropospheric Humidity, and the Greenhouse Effect

This paper combines satellite measurements of the upwelling 6.7-μm radiance from TOVS with cloud-property information from ISCCP and outgoing longwave radiative fluxes from ERBE to analyze the climatological interactions between deep convection, upper-tropospheric humidity, and atmospheric greenhouse trapping. The satellite instruments provide unmatched spatial and temporal coverage, enabling detailed examination of regional, seasonal, and interannual variations between these quantities. The present analysis demonstrates that enhanced tropical convection is associated with increased upper-tropospheric relative humidity. The positive relationship between deep convection and upper-tropospheric humidity is observed for both regional and temporal variations, and is also demonstrated to occur over a wide range of space and time scales. Analysis of ERBE outgoing longwave radiation measurements indicates that regions or periods of increased upper-tropospheric moisture are strongly correlated with an enhanced greenhouse trapping, although the effects of lower-tropospheric moisture and temperature lapse rate are also observed to be important. The combined results for the Tropics provide a picture consistent with a positive interrelationship between deep convection, upper-tropospheric humidity, and the greenhouse effect. In extratropical regions, temporal variations in upper-tropospheric humidity exhibit little relationship to variations in deep convection, suggesting the importance of other dynamical processes in determining changes in upper-tropospheric moisture for this region. Comparison of the observed relationships between convection, upper-tropospheric moisture, and greenhouse trapping with climate model simulations indicates that the Geophysical Fluid Dynamics Laboratory (GFDL) GCM is qualitatively successful in capturing the observed relationship between these quantities. This evidence supports the ability of the GFDL GCM to predict upper-tropospheric water vapor feedback, despite the model's relatively simplified treatment of moist convective processes.

Sea surface temperature, low‐level moisture, and convection in the tropical Pacific, 1982–1985

Sea surface temperature (SST), lower tropospheric moisture, and deep convection in the tropical Pacific are described and compared for the period January 1982 through December 1985. All the data used were wholly or partially satellite derived, enabling the examination of continuous fields over large areas. SST data were from the blended analysis produced by the Climate Analysis Center, low‐level precipitable water (LLPW) in the 1000‐ to 700‐mbar layer was derived from the TIROS‐N operational vertical sounder aboard the NOAA polar‐orbiting satellites, and deep convection was estimated from the presence of highly reflective clouds (HRC) visible on NOAA satellite picture mosaics. Monthly means of LLPW and HRC were computed from daily data to correspond to the averaging period of SST. Maxima and minima of the three variables were found to be offset in both time and space, demonstrating that high SST does not always result in enhanced local convection. In the eastern equatorial Pacific, increases of SST and LLPW were found to precede rises of HRC by 1 or more months. Variability of all three parameters in the eastern Pacific was dominated by the 1982–83 El Niño‐Southern Oscillation and the seasonal cycle, whereas the seasonal cycle of all parameters in the western and central Pacific was weak. The strong signals in the eastern equatorial Pacific were in part responsible for the higher correlation coefficients between all pairs of variables there. Recent modeling studies are beginning to take into account the complexity of atmospheric response to surface heating.

Delineating Mid- and Low-Level Water Vapor Patterns in Pre-Convective Environments Using VAS Moisture Channels

Infrared and visible imagery from VAS are used to delineate mid- and lower-tropospheric moisture fields for a variety of severe storm cases in the southern and central United States. The ability of sequences of images to isolate areas of large negative vertical moisture gradients and apparent convective instability prior to the onset of convective storms is assessed. A variety of image combination procedures are used to deduce the stability fields which are then compared with the available radiosonde data. The results for several severe storm cases indicate that VAS can detect mid- and low-level mesoscale water vapor fields as distinct radiometric signals. The VAS imagery shows a strong tendency for thunderstorms to develop along the edges of bands of midlevel dryness as they overtake either preexisting or developing low-level moisture maxima. Image sequences depict the speed with which deep moist and dry layers can develop and move.

Determination of Moisture From NOAA Polar Orbiting Satellite Sounding Radiances

A method is presented for deducing lower troposphere moisture fields from radiances measured by the operational polar orbiting NOAA satellites. Statistical evaluation of the technique demonstrates the viability of the approach. A case study with TIROS-N observations shows substantial improvement over current operational methods, and a qualitatively reasonable product. High moisture gradients are clearly defined and horizontal consistency is achieved. The technique appears useful for the initialization of subsynoptic forecast models.