Ground-based Microwave Radiometer Research Articles

Microwave and Millimeter-Wave Radiometric and Radiosonde Observations in an Arctic Environment

Abstract In a recent paper by Mattioli et al., a significant difference was observed between upper-tropospheric and lower-stratospheric water vapor profiles as observed by two radiosonde systems operating in the Arctic. The first was the Vaisala RS90 system as operated by the U.S. Department of Energy’s Atmospheric Radiation Measurement Program; the second was the operational radiosondes launched by the U.S. National Weather Service that used the Sippican VIZ-B2 type. Observations of precipitable water vapor by ground-based microwave radiometers and GPS did not reveal these differences. However, both the microwave radiometer profiler (MWRP) and the ground-based scanning radiometer (GSR) contain channels that receive a significant response from the upper-tropospheric region. In this paper, it is shown that brightness temperature (Tb) observations from these instruments are in consistent agreement with calculations based on the RS90 data but differ by several degrees with calculations based on the VIZ radiosondes. It is also shown that calculations of Tb can serve as a gross quality control of upper-tropospheric soundings.

Application of microwave radiometer and wind profiler data in the estimation of wind gust associated with intense convective weather

Estimates of the wind gusts associated with intense convective weather could be obtained using empirical relationships such as GUSTEX based on radiosonde measurements. However, such data are only available a couple of times a day and may not reflect the rapidly changing atmospheric condition in spring and summer times. The feasibility of combining the thermodynamic profiles from a ground-based microwave radiometer and wind profiles given by radar wind profilers in the continuous estimation of wind gusts is studied in this paper. Based on the results of a 4-month trial of a microwave radiometer in Hong Kong in 2004, the estimated and the actual gusts are reasonably well correlated. It is also found that the wind gusts so estimated provide better indications of the strength of squalls compared with those based on radiosonde measurements and with a lead time of about one hour.

Determination of Richardson number profile from remote sensing data and its aviation application

A number of remote-sensing wind-measuring instruments, such as LIDAR and radar wind profilers, have been set up in the vicinity of the Hong Kong International Airport (HKIA) for monitoring of low-level windshear and turbulence. The combined usage of wind data from a radar wind profiler and boundary layer temperature profiles from a ground-based microwave radiometer in turbulence application is studied in this paper. Data collected in a field experiment of the radiometer conducted in Hong Kong in February 2006 were used to obtain the Richardson number profile up to 1.5 km above ground. Two examples of atmospheric turbulence reported by the pilots are considered. The Richardson number profiles are found to capture the turbulence events reasonably well. The evolution of these profiles and airflow disruption by the nearby terrain as a possible cause of the turbulence will also be discussed.

Characterization of Errors in a Coupled Snow Hydrology–Microwave Emission Model

Abstract Traditional approaches to the direct estimation of snow properties from passive microwave remote sensing have been plagued by limitations such as the tendency of estimates to saturate for moderately deep snowpacks and the effects of mixed land cover within remotely sensed pixels. An alternative approach is to assimilate satellite microwave emission observations directly, which requires embedding an accurate microwave emissions model into a hydrologic prediction scheme, as well as quantitative information of model and observation errors. In this study a coupled snow hydrology [Variable Infiltration Capacity (VIC)] and microwave emission [Dense Media Radiative Transfer (DMRT)] model are evaluated using multiscale brightness temperature (TB) measurements from the Cold Land Processes Experiment (CLPX). The ability of VIC to reproduce snowpack properties is shown with the use of snow pit measurements, while TB model predictions are evaluated through comparison with Ground-Based Microwave Radiometer (GBMR), aircraft [Polarimetric Scanning Radiometer (PSR)], and satellite [Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E)] TB measurements. Limitations of the model at the point scale were not as evident when comparing areal estimates. The coupled model was able to reproduce the TB spatial patterns observed by PSR in two of three sites. However, this was mostly due to the presence of relatively dense forest cover. An interesting result occurs when examining the spatial scaling behavior of the higher-resolution errors; the satellite-scale error is well approximated by the mode of the (spatial) histogram of errors at the smaller scale. In addition, TB prediction errors were almost invariant when aggregated to the satellite scale, while forest-cover fractions greater than 30% had a significant effect on TB predictions.

Diurnal Variation of Water Vapor Mixing between the Atmospheric Boundary Layer and Free Atmosphere over Changwu, the Loess Plateau in China

We investigated the diurnal variation of water vapor mixing between the atmospheric boundary layer (ABL) and the free atmosphere over the Loess Plateau in China. Water vapor and wind velocity in the troposphere were observed using a ground-based microwave radiometer and a wind profiler radar in 2005 and 2006. On sunny days in early summer, a strong vertical wind was generated in the afternoon followed by ABL development. Strong convection was enhanced when active cumulus convection developed in the afternoon. In such cases, water vapor decreased in the lower atmosphere from the early morning until late afternoon, while water vapor increased in the upper atmosphere. This finding suggests that water vapor was exchanged diurnally between the ABL and the free atmosphere. The strong convection in the ABL, which was developed by sensible heat from the land surface, played critical roles with link to cumulus convection in such vertical mixing of water vapor. Influences of other processes such as a local circulation and advection of cloud systems were also discussed.

Comparison and synergy of stratospheric ozone measurements by satellite limb sounders and the ground-based microwave radiometer SOMORA

Abstract. Stratospheric O3 profiles obtained by the satellite limb sounders Aura/MLS, ENVISAT/MIPAS, ENVISAT/GOMOS, SAGE-II, SAGE-III, UARS/HALOE are compared to coincident O3 profiles of the ground-based microwave radiometer SOMORA in Switzerland. Data from the various measurement techniques are within 10% at altitudes below 45 km. At altitudes 45–60 km, the relative O3 differences are within a range of 50%. Larger deviations at upper altitudes are attributed to larger relative measurement errors caused by lower O3 concentrations. The spatiotemporal characteristics of the O3 differences (satellite – ground station) are investigated by analyzing about 2300 coincident profile pairs of Aura/MLS (retrieval version 1.5) and SOMORA. The probability density function of the O3 differences is represented by a Gaussian normal distribution. The dependence of the O3 differences on the horizontal distance between the sounding volumes of Aura/MLS and SOMORA is derived. While the mean bias (Aura/MLS – SOMORA) is constant with increasing horizontal distance (up to 800 km), the standard deviation of the O3 differences increases from around 8 to 11% in the mid-stratosphere. Geographical maps yield azimuthal dependences and horizontal gradients of the O3 difference field around the SOMORA ground station. Coherent oscillations of O3 are present in the time series of Aura/MLS and SOMORA (e.g., due to traveling planetary waves). Ground- and space-based measurements often complement one another. We discuss the double differencing technique which allows both the cross-validation of two satellites by means of a ground station and the cross-validation of distant ground stations by means of one satellite. Temporal atmospheric noise in the geographical ozone map over Payerne is significantly reduced by combination of the data from SOMORA and Aura/MLS. These analyses illustrate the synergy of ground-based and space-based measurements.

Comparison of Calibration Techniques for Ground-Based C-Band Radiometers

We quantify the performance of three commonly used techniques to calibrate ground-based microwave radiometers for soil moisture studies, external (EC), tipping-curve (TC), and internal (IC). We describe two ground-based C-band radiometer systems with similar design and the calibration experiments conducted in Florida and Alaska using these two systems. We compare the consistency of the calibration curves during the experiments among the three techniques and evaluate our calibration by comparing the measured brightness temperatures (TBs) to those estimated from a lake emission model (LEM). The mean absolute difference among the TBs calibrated using the three techniques over the observed range of output voltages during the experiments was 1.14 K. Even though IC produced the most consistent calibration curves, the differences among the three calibration techniques were not significant. The mean absolute errors (MAEs) between the observed and LEM TB s were about 2-4 K. As expected, the utility of TC at C-band was significantly reduced due to transparency of the atmosphere at these frequencies. Because IC was found to have a MAE of about 2 K that is suitable for soil moisture applications and was consistent during our experiments under different environmental conditions, it could augment less frequent calibrations obtained using the EC or TC techniques

Three-dimensional effects in polarization signatures as observed from precipitating clouds by low frequency ground-based microwave radiometers

Abstract. Consistent negative polarization differences (i.e. differences between the vertical and the horizontal brightness temperature) are observed when looking at precipitating systems by ground-based radiometers at slant angles. These signatures can be partially explained by one-dimensional radiative transfer computations that include oriented non-spherical raindrops. However some cases are characterized by polarization values that exceed differences expected from one-dimensional radiative transfer. A three-dimensional fully polarized Monte Carlo model has been used to evaluate the impact of the horizontal finiteness of rain shafts with different rain rates at 10, 19, and 30 GHz. The results show that because of the reduced slant optical thickness in finite clouds, the polarization signal can strongly differ from its one-dimensional counterpart. At the higher frequencies and when the radiometer is positioned underneath the cloud, significantly higher negative values for the polarization are found which are also consistent with some observations. When the observation point is located outside of the precipitating cloud, typical polarization patterns (with troughs and peaks) as a function of the observation angle are predicted. An approximate 1-D slant path radiative transfer model is considered as well and results are compared with the full 3-D simulations to investigate whether or not three-dimensional effects can be explained by geometry effects alone. The study has strong relevance for low-frequency passive microwave polarimetric studies.

The STARTWAVE atmospheric water database

Abstract. The STARTWAVE (STudies in Atmospheric Radiative Transfer and Water Vapour Effects) project aims to investigate the role which water vapour plays in the climate system, and in particular its interaction with radiation. Within this framework, an ongoing water vapour database project was set up which comprises integrated water vapour (IWV) measurements made over the last ten years by ground-based microwave radiometers, Global Positioning System (GPS) receivers and sun photometers located throughout Switzerland at altitudes between 330 and 3584 m. At Bern (46.95° N, 7.44° E) tropospheric and stratospheric water vapour profiles are obtained on a regular basis and integrated liquid water, which is important for cloud characterisation, is also measured. Additional stratospheric water vapour profiles are obtained by an airborne microwave radiometer which observes large parts of the northern hemisphere during yearly flight campaigns. The database allows us to validate the various water vapour measurement techniques. Comparisons between IWV measured by the Payerne radiosonde with that measured at Bern by two microwave radiometers, GPS and sun photometer showed instrument biases within ±0.5 mm. The bias in GPS relative to sun photometer over the 2001 to 2004 period was –0.8 mm at Payerne (46.81° N, 6.94° E, 490 m), which lies in the Swiss plains north of the Alps, and +0.6 mm at Davos (46.81° N, 9.84° E, 1598 m), which is located within the Alps in the eastern part of Switzerland. At Locarno (46.18° N, 8.78° E, 366 m), which is located on the south side of the Alps, the bias is +1.9 mm. The sun photometer at Locarno was found to have a bias of –2.2 mm (13% of the mean annual IWV) relative to the data from the closest radiosonde station at Milano. This result led to a yearly rotation of the sun photometer instruments between low and high altitude stations to improve the calibrations. In order to demonstrate the capabilites of the database for studying water vapour variations, we investigated a front which crossed Switzerland between 18 November 2004 and 19 November 2004. During the frontal passage, the GPS and microwave radiometers at Bern and Payerne showed an increase in IWV of between 7 and 9 mm. The GPS IWV measurements were corrected to a standard height of 500 m, using an empirically derived exponential relationship between IWV and altitude. A qualitative comparison was made between plots of the IWV distribution measured by the GPS and the 6.2 µm water vapour channel on the Meteosat Second Generation (MSG) satellite. Both showed that the moist air moved in from a northerly direction, although the MSG showed an increase in water vapour several hours before increases in IWV were detected by GPS or microwave radiometer. This is probably due to the fact that the satellite instrument is sensitive to an atmospheric layer at around 320 hPa, which makes a contribution of one percent or less to the IWV.

Comparison of brightness temperatures observed from ground-based microwave radiometers during TUC

The agreement of two ground-based microwave radiometers during the Temperature, hUmidity, and Cloud (TUC) profiling campaign has been evaluated in terms of measured brightness temperature. To account effectively the instruments' specifications, we discuss and estimate an equivalent monochromatic frequency, which significantly reduces the bias introduced by ideal monochromatic modelling. The effect of this equivalent monochromatic frequency can reach 0.4 K and thus we recommend its use in further study involving TUC radiometers. This analysis showed agreement within expectations for three of the four selected pairs of channels, although results are strictly valid in a limited range. As a consequence, the derived products are expected to be of the same quality. However, the inconsistency found in the remaining pair is expected to propagate in the retrieved humidity profiles.

Temperature and humidity profile retrievals from ground-based microwave radiometers during TUC

Thermodynamic atmospheric profiles have been retrieved from ground-based microwave radiometers during the Temperature, hUmidity, and Cloud (TUC) profiling campaign. A variety of inversion methods is presented, in terms of requirements, advantages, and limitations. Results confirm the theoretical expectation that retrievals’ accuracy and resolution degrade steadily with height up to 3 km, then more rapidly. At higher levels the retrievals’ accuracy does not improve on that of a Numerical Weather Prediction model, which provides a background for the variational technique. Most retrieval methods produce a bias in the temperature profile above 1 km, which may be due to a bias in the absorption model used and/or observations at 51–54 GHz. Elevation scanning is shown to improve the accuracy and resolution of the retrievals in the boundary layer, but is limited by technical shortcomings. Zusammenfassung Thermodynamische atmospharische Profile wurden mit bodengestutzten Mikrowellenradiometern wahrend der Temperature, hUmidity, and Cloud (TUC) profiling Kampagne gemessen. Verschiedene Inversionsmethoden werden in Bezug auf Anforderungen, Vorteile und Einschrankungen vorgestellt. Die Resultate bestatigen die theoretische Erwartung, dass die Genauigkeit und die Auflosung der gemessenen Profile kontinuierlich bis 3 km Hohe schwach und daruber starker abnehmen. In den hoheren Schichten ist die Genauigkeit der Profile nicht besser als die des numerischen Wettervorhersagemodells, das die Hintergrundfelder fur das erorterte Variationsverfahren bereitstellt. Die meisten Inversionsmethoden fuhren zu systematischen Fehlern in den gemessenen Profilen oberhalb von 1 km, was auf systematische Fehler im verwendeten Absorptionsmodell und/oder bei der Messung der Helligkeitstemperatur zwischen 51 und 54 GHz hindeutet. Die zusatzliche Einbeziehung von Messungen unterschiedlicher Elevationswinkel verbessern die Genauigkeit und die Auflosung der abgeleiteten Profile in der planetaren Grenzschicht, wobei die Vorteile durch technische Unzulanglichkeiten eingeschrankt sind.

SNOW SATELLITE ALGORITHM VERIFICATION BESED ON THE GROUND SNOW OBSERVATION USING A GROUND MICROWAVE RADIOMETER

In the previous research, we developed a snow algorithm for snow depth and snow grain size based on the microwave radiative transfer theory and validated by using the in-situ snow depth data at the ground-based stations in the northern hemisphere and the Advanced Microwave Scanning Radiometer for the Earth Observation System (AMSR-E) on Aqua launched by NASA in 2002.In this study, we verified the correctness of this snow satellite algorithm by the ground snow observation using the ground microwave radiometer (GBMR (Ground Based Microwave Radiometer)) in Sapporo. In the cases with the wet snow, the results of validation were shown poor correspondence of observation value and estimation value. In contrast, in the cases with the dry snow, the results of validation were shown good correspondence of observation value and estimation value.

Monitoring of melting refreezing cycles of snow with microwave radiometers: the Microwave Alpine Snow Melting Experiment (MASMEx 2002-2003)

A study of the melting cycle of snow was carried out by using ground-based microwave radiometers, which operated continuously 24 h/day from late March to mid-May in 2002 and from mid-February to early May in 2003. The experiment took place on the eastern Italian Alps and included micrometeorological and conventional snow measurements as well. The measurements confirmed the high sensitivity of microwave emission at 19 and 37 GHz to the melting-refreezing cycles of snow. Moreover, micrometeorological data made it possible to simulate snow density, temperature, and liquid water content through a hydrological snowpack model and provided additional insight into these processes. Simulations obtained with a two-layer electromagnetic model based on the strong fluctuation theory and driven by the output of the hydrological snowpack model were consistent with experimental data and allowed interpretation of both variation in microwave emission during the melting and refreezing phases and in discerning the contributions of the upper and lower layers of snow as well as of the underlying ground surface.

Microphysical Processes and Synergistic Interaction between Frontal and Orographic Forcing of Precipitation during the 13 December 2001 IMPROVE-2 Event over the Oregon Cascades

Abstract On 13–14 December 2001 a vigorous cyclonic storm passed over the Pacific Northwest, producing heavy orographic precipitation over the Cascade Mountains. This storm was one of several studied during the second field phase of the Improvement of Microphysical Parameterization through Observational Verification Experiment (IMPROVE). A wide variety of in situ and remotely sensed measurements were obtained as this storm passed over the Oregon Cascades. These measurements provided a comprehensive dataset of meteorological state parameters (temperature, pressure, humidity, winds, and vertical air velocity), polarization Doppler radar measurements, and cloud microphysical parameters (cloud liquid water, particle concentrations, size spectra, and imagery). The 13–14 December case was characterized by the passage of a tipped-forward lower-tropospheric front that extended upward to a preceding vigorous upper cold-frontal rainband, which produced clouds up to ∼8–9 km. An important difference between this storm and those studied previously over the Washington Cascades was that the prefrontal low-level airflow over the Oregon Cascades was characterized by strong westerly (as opposed to weak easterly) cross-barrier flow. Consequently, as the upper cold-frontal band passed over the Oregon Cascades there was both strong ice particle production aloft and significant production of liquid water at lower levels in the orographic lifting zone. Airborne in situ measurements, ground-based microwave radiometer measurements, and observations of snow crystals showed the simultaneous presence of high ice crystal concentrations and relatively large values of cloud liquid water aloft, and heavily rimed particles reaching the ground. Analyses indicate that a synergistic interaction occurred between the frontal and orographic precipitation.

Intercomparison of O<sub>3</sub> profiles observed by SCIAMACHY and ground based microwave instruments

Abstract. Ozone profiles retrieved from limb scattering measurements of the SCIAMACHY instrument based on the satellite ENVISAT are compared to ground-based low altitude resolution remote sensors. All profiles are retrieved using optimal estimation. Following the work of Rodgers and Connor (2003) the retrievals of the ground-based instruments are simulated using the SCIAMACHY retrieval. The SCIAMACHY results and the results of the ground-based microwave radiometer in Bremen and Ny Ålesund agree within the expected covariance of the intercomparison.

Comparison of MM5 integrated water vapor with microwave radiometer, GPS, and radiosonde measurements

A large dataset of concurrent integrated precipitable water vapor (IPWV) estimates from ground-based microwave radiometers (MWRs), global positioning system (GPS) ground-receivers, and radiosonde observations (RAOBs) has been collected in five different sites in Central Italy. Both MWRs and GPS have shown a capability of accurate and continuous water vapor monitoring. These data are used to study the seasonal and spatial variability of IPWV. A comparison of these data with the IPWV field produced operationally by the nonhydrostatic Mesoscale Model (MM5), running at the University of L'Aquila/Center of Excellence (CETEMPS) is performed in order to find either model shortcomings and to corroborate the IPWV behavior highlighted by the measurements. Both measurements and model outputs span over a period of about one year allowing for a systematic statistical analysis for all the examined stations. The statistical analysis shows a good agreement between GPS and MWR data, whereas discrepancies are found between RAOBs and the other techniques. The IPWV shows the largest diurnal variability, approximately 3%, during the summer season. An overall good agreement is found between the forecasted and observed IPWV. The related statistical parameters show a very low bias (0.001 cm) with a good correlation coefficient (0.939). On the other hands, the seasonal analyses highlight a few discrepancies, mostly due to the MM5 difficulties in correctly forecasting the diurnal cycle.

A GBMR Experiment and Validation of 1DVAR-LDAS in Different Bare Soil

Land surface variables, especially the soil moisture, are central to the regulation of the land-atmosphere water, energy, and carbon interactions. The development of land hydrological parameterizations that emphasize soil moisture and temperature, together with innovative remote sensing and surface-based observations, promise a mechanism for the synthesis of regional fields of these vital hydrological variables. Data assimilation is the process of incorporating observations into a model of the land-atmosphere interaction system and filling the region of missing data with model predictions as well as providing a suite of data-constrained estimates of unobserved quantities. In order to incorporate remote sensing and surface-based observations in a numerical forecasting model that estimates land-surface parameters, we have developed a Land Data Assimilation Scheme (LDAS) that can assess the model parameters and estimates vertical profiles of soil moisture and temperature by comparing passive microwave observations through a unique minimization technique called Very Fast Simulated Annealing (VFSA). This manuscript mainly focuses on modifying LDAS and testing its capabilities in different bare soils and their surface conditions. So we conducted a field experiment and obtained well-controlled observations by employing a six channel Ground Based Microwave Radiometer (GBMR-6CH). The results of the LDAS testing were in good agreement with observational data compare to open loop simulations. Major model sensitivities to soil type, soil moisture, and surface roughness are explored in bellow section.

Recent improvements to LWP retrievals from AVHRR

In the framework of the Cloud Liquid Water Network (CLIWA-NET) project, an attempt is made to reconstruct the spatial distribution of liquid water path (LWP) by combining data from a network of ground-based microwave radiometers with imagery of the Advanced Very High Resolution Radiometer (AVHRR). In order to provide atmospheric modelers sufficient high-quality reference data for model evaluation and improvement, measurements from three intensive measurement campaigns are analyzed. This paper describes the AVHRR quantitative cloud analysis environment that was developed and tested at the Royal Netherlands Meteorological Institute (KNMI) during the project. The environment is named KLAROS (KNMI Local Implementation of APOLLO in an Operational System). KLAROS includes retrieval of a suite of physical cloud parameters. In order to evaluate the liquid water path retrieval, ground-based radiometer measurements are used. A new technique, called the Russian doll method, is introduced to assess the relation between ground and satellite measurements. This relation depends on the variability in time and space of the observed cloud fields and shows up clearly in the Russian doll diagrams. First, results from the comparisons give confidence that KLAROS gives plausible liquid water path values. We find that AVHHR data from the NOAA-16 platform is much better suited for quantitative cloud analysis than its predecessors. In particular, the availability of a 1.6-μm channel and the good calibration contribute to the improved accuracies. The retrieval method for liquid water path will be implemented in the framework of the Satellite Application Facility of Climate Monitoring (CM-SAF).

Quality assessment of ground-based microwave measurements of chlorine monoxide, ozone, and nitrogen dioxide from the NDSC radiometer at the Plateau de Bure

Abstract. A ground-based microwave radiometer dedicated to chlorine monoxide (ClO) measurements around 278GHz has been in operation from December 1993-June 1996 at the Plateau de Bure, France (45° N, 5.9° E, 2500m altitude). It belongs to the international Network for the Detection of Stratospheric Change. A detailed study of both measurements and retrieval schemes has been undertaken. Although dedicated to the measurements of ClO, simultaneous profiles of O3, ClO and NO2, together with information about the instrumental baseline, have been retrieved using the optimal estimation method. The vertical profiles have been compared with other ground-based microwave data, satellite-borne data and model results. Data quality shows: 1) the weak sensitivity of the instrument that obliges to make time averages over several hours; 2) the site location where measurements of good opacities are possible for only a few days per year; 3) the baseline undulation affecting all the spectra, an issue common to all the microwave instruments; 4) the slow drift of some components affecting frequencies by 3-4MHz within a couple of months. Nevertheless, when temporally averaging data over a few days, ClO temporal variations (diurnal and over several weeks in winter 1995) from 35-50km are consistent with model results and satellite data, particularly at the peak altitude around 40km, although temporal coincidences are infrequent in winter 1995. In addition to ClO, it is possible to obtain O3 information from 30-60km whilst the instrument is not optimized at all for this molecule. Retrievals of O3 are reasonable when compared with model and another ground-based data set, although the lowermost layers are affected by the contamination of baseline remnants. Monthly-averaged diurnal variations of NO2 are detected at 40km and appear in agreement with photochemical model results and satellite zonally-averaged data, although the amplitude is weaker than the other data sets. This NO2 result highlights the great potential of the retrieval scheme used.

Statistical Study on Precipitable Water Content Variations Observed with Ground-Based Microwave Radiometers

GPS analysis requires statistical information on temporal variations of precipitable water vapor content (PWC), since temporal variability of PWC is assumed in the analyses. Spatial scales of PWC variations also are necessary for incorporation of the analyzed GPS data into numerical weather prediction systems. The objective of the present study is to investigate temporal and spatial characteristics of the PWC variations in Japan. For this purpose, slant-path PWC was observed with ground-based microwave radiometers (MWRs) for the directions of GPS satellites in the eastern part of the Kanto Plain during several observation periods in 2000 and 2001. Three components, vertical PWC, horizontal gradient and higher-order inhomogeneity, were retrieved from the slant-path observation data. Deviations of vertical PWC from ten-day averages (hereafter referred to as vertical deviations) were then calculated in order to remove seasonal changes of this component. Simultaneous observation data at three MWR sites also were used for the rough estimation of horizontal scales of the three PWC components. The results show: 1) The vertical deviations marked were about 20 times as large amplitudes as the other two components, while the variations due to the gradient had even smaller amplitudes than the inhomogeneity; 2) The vertical deviations had large spectral power against periods around 5-6 days and 8-9 days, while the gradient was dominated by diurnal variations; and, 3) It was roughly estimated that the vertical deviations (gradient) had the horizontal scales of several hundred (several ten) kilometers. The horizontal scale of the PWC inhomogeneity was considered to be less than 10 km. The vertical deviations (the gradient) were considered to be closely related with large-scale meteorological disturbances (local-scale circulations) on the basis of the above temporal and spatial characteristics.