Water Vapor Mixing Ratio Profiles Research Articles

Observations of water vapor mixing ratio profile and flux in the Tibetan Plateau based on the lidar technique

Abstract. As a part of the third Tibetan Plateau Experiment of Atmospheric Sciences (TIPEX III) in China, a Raman water vapor, cloud and aerosol lidar and a coherent wind lidar were operated in Naqu (31.48° N, 92.06° E) with a mean elevation of more than 4500 m a.m.s.l. in summer of 2014. During the field campaign, the water vapor mixing ratio profiles were obtained and validated by radiosonde observations. The mean water vapor mixing ratio in Naqu in July and August was about 9.4 g kg−1 and the values vary from 6.0 to 11.7 g kg−1 near the ground according to the lidar measurements, from which a diurnal variation of water vapor mixing ratio in the planetary boundary layer was also illustrated in this high-elevation area. Furthermore, using concurrent measurements of vertical wind speed profiles from the coherent wind lidar, we calculated the vertical flux of water vapor that indicates the water vapor transport through updraft and downdraft. The fluxes were for a case at night with large-scale non-turbulent upward transport of moisture. It is the first application, to our knowledge, to operate continuously atmospheric observations by utilizing multi-disciplinary lidars at the altitude higher than 4000 m, which is significant for research on the hydrologic cycle in the atmospheric boundary layer and lower troposphere in the Tibetan Plateau.

Comparing Water Vapor Mixing Ratio Profiles and Cloud Vertical Structure from Multiwavelength Raman Lidar Retrievals and Radiosounding Measurements

A study of comparison of water vapor mixing ratio profiles, relative humidity profiles, and cloud vertical structures using two different instruments, a multiwavelength Aerosol-Depolarization-Raman lidar and radiosoundings, is presented. The observations were taken by the lidar located in Warsaw center and the radiosoundings located about 30km to the North in Legionowo (Poland). We compared the ground-based remote sensing technology with in-situ method in order to improve knowledge about water content thought the atmosphere and cloud formation. The method used for retrieving the cloud vertical structure can be improved comparing the radiosonde results with the lidar observations, which show promising results.

Water Vapor Profiles up to the UT/LS from Raman Lidar at Reunion Island (21°S, 55°E) : Technical Description, Data Processing and Comparison with Sondes

The Maido high-altitude observatory located in Reunion Island (21°S, 55°E) is equipped with an innovative lidar designed to monitor the water vapor in the whole troposphere up to the lower stratosphere with a Raman system and to monitor, simultaneously, the temperature in the stratosphere and in the mesosphere based on a Rayleigh scattering technique. Several improvements have been performed on the new instrument to optimize the water vapor mixing ratio measurements thanks to the experience of the previous system. The choice of the operational configuration of the system and the calibration methodology were realized during the campaign MALICCA-1 (MAido LIdar Calibration CAmpaign) which provided simultaneous measurements of water vapor and ozone in April 2013. The lidar water vapor profiles are calibrated with water vapor columns obtained from a collocated GNSS receiver. By comparing CFH and Vaisala radiosondes and satellites water vapor mixing ratio profiles with the Raman lidar profiles, the performances of the lidar are shown to be good in the troposphere. With a suitable integration time period, the ability of measuring quantities of a few ppmv in the lower stratosphere is demonstrated. This Raman lidar will provide regular measurements to international networks with high vertical resolution profiles of water vapor in order to document various studies and to insure a long-term survey of the troposphere and of the lower stratosphere.

An Autonomous Polarized Raman Lidar System Designed for Summit Camp, Greenland

A dearth of high-spatial and temporal resolution measurements of atmospheric state variables in the Arctic directly inhibits scientific understanding of radiative and precipitation impacts on the changing surface environment. More reliable and frequent measurements are needed to better understand Arctic weather processes and constrain model predictions. To partially address the lack of Artic observations, a new autonomous Raman lidar system, which will measure water vapor mixing ratio, temperature, extinction, and cloud phase profiles through the troposphere, is designed for deployment to Summit Camp, Greenland (72° 36' N, 38° 25' W, 3250 [m]). This high-altitude Arctic field site has co-located ancillary equipment such as a Doppler millimeter cloud radar, microwave radiometers, depolarization lidars, ceiliometer, an infrared interferometer and twice-daily radiosondes. The current suite of instruments allows for a near comprehensive picture of the atmospheric state above Summit but increased spatial and temporal resolution of water vapor and temperature will reveal detailed microphysical information. A system description will be provided with an emphasis on the Monte Carlo safety analysis done to ensure eye safety in all relevant weather conditions.

A multi‐instrument and multi‐model assessment of atmospheric moisture variability over the western Mediterranean during HyMeX

The Hydrological cycle in the Mediterranean eXperiment (HyMeX) was held in autumn 2012 during which part of the observational effort was established on Menorca Island to characterize the upwind marine low‐level flow. The ground‐based Water‐vapour Raman Lidar (WALI), the airborne water‐vapour lidar LEANDRE 2 and boundary‐layer pressurized balloons were implemented during the first Special Observing Period and contributed to characterize water vapour variability in the vicinity of the Balearic Islands, together with the existing network of Global Positioning System receivers. Furthermore, analyses from regional and global numerical weather prediction (NWP) models (AROME‐WMED, the ECMWF/IFS NWP system and the Weather Research and Forecasting (WRF) model) were also available over large domains encompassing part of or the entire western Mediterranean basin. We assess the consistency of water vapour mixing ratio (WVMR) profiles and integrated water vapour contents (IWVC) derived from the different datasets by comparing them to a common reference, the ground‐based lidar WALI. We use consistency indicators such as root‐mean‐square errors, biases and correlations. Comparison between WVMR profiles from ground‐based and airborne lidars (ground‐based lidar and boundary‐layer pressurized balloons) leads to a root‐mean‐square error lower than 1.6 g kg−1 (1.3 g kg−1) when the closest possible air masses are sampled. We observed a good agreement between the vertical WVMR profiles derived from WALI and the numerical models with correlations higher than 0.7 and root‐mean‐square errors lower than 2 g kg−1. Regarding IWVCs, the models exhibit biases less than 2 kg m−2, root‐mean‐square errors lower than 2.3 g kg−1 and correlations higher than 0.86 when compared to WALI. Finally, AROME‐WMED 48 h forecasts were compared with WALI data composited over eleven 48 h periods. The quality of the forecast does not visibly degrade within the 48 h period from the initial analyses.

Numerical simulations with the WRF model of water vapour vertical profiles: A comparison with LIDAR and radiosounding measurements

Numerical simulations with the Advanced Research-Weather Research and Forecasting model (WRF-ARW) have been performed in order to simulate water vapor mixing ratio (WVMR) vertical profiles over southeastern Italy. An optimal setup of the model has been identified changing the default model land cover database and using a fine model vertical resolution in the lower levels. Among different tests, the selected implementation is the one that best reproduced the experimental WVMR profiles retrieved from the Brindisi radiosounding station and the ground-based Raman lidar measurements at Lecce site.The use of the WRF model to simulate WVMR profiles along the tracks of the spaceborne lidar CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) on two case studies has revealed that numerical models are reliable tools, particularly useful when no ground measurements of water vapor are available. In particular, it is shown that the inhomogeneous distribution of moisture in the domain, as emerging from the model simulations, may significantly affect the CALIOP validation procedures. Such procedures are based on the intercomparison of the satellite retrieved aerosol profiles with those measured, nearly at the same time, with a ground-based lidar located few km away from the sites where CALIOP aerosol products are delivered in the selected events.

Long-Term Measurement for Low-Tropospheric Water Vapor and Aerosol by Raman Lidar in Wuhan

A Raman Lidar (RL) system is developed to measure the water vapor mixing ratio (WVMR) and aerosol optical property in Wuhan with high temporal-spatial resolution during rainless nights. The principle of the self-developed lidar system and data processing method are discussed. WVMR profiles of a representative case retrieved by RL, Radiosonde (RS), and microwave radiometer (MR) are in good agreement. The relationship of WVMR and aerosol optical depth (AOD) indicates that water vapor dramatically reduces with the decline of the AOD. Moreover, the mean relative difference of mean WVMRs at low-troposphere obtained by RL and RS (MR) is about 5.17% (9.47%) during the analyzed year. The agreement certifies that the self-developed RL system can stably provide accurate and high temporal-spatial resolution data for the fundamental physical studies on water vapor. Furthermore, the maximum AOD from 0.5 km to 3 km is 0.41 at night in spring, which indicates that the air quality in Wuhan is heavily influenced by aerosols that are transported by air mass from the north during this time. Moreover, abundant rainfall led to relatively low AOD in summer (0.22), which demonstrates that water vapor is crucial for air purification.

Lidar vertical profiling of water vapor and aerosols in the Great Lakes Region: A tool for understanding lower atmospheric dynamics

Results of a recently developed water vapor Raman lidar instrument at Environment Canada's Center for Atmospheric Research Experiments (CARE) are shown for selected days of summer and winter seasons. The basic components of the Raman water vapor lidar consist of a 30Hz, Q-switched Nd:YAG high-powered laser utilizing the third harmonic (355nm), beam steering optics, a 0.76m Cassegrain telescope and three detection channels to simultaneously observe the vertical profiles of aerosols, water vapor, and nitrogen from near ground up to 9.5km. By manipulating the inelastic backscattering lidar signals from the Raman nitrogen channel (386.7nm) and Raman water vapor channel (407.5nm), vertical profiles of water vapor mixing ratio (WVMR) are deduced, calibrated, and compared against WVMR profiles obtained from coincident and collocated radiosonde profiles. The average standard deviation, in the water vapor mixing ratio, is estimated to be less than 10% between the sonde and lidar measurements. In addition, comparisons between simultaneous WVMR profiles and aerosol profiles obtained from a simple aerosol backscatter lidar, also located at the CARE facility, provide insight into the complex dynamic mixing of the lower atmosphere and their subsequent impact on climate and air quality.

Quantifying the value of redundant measurements at GCOS Reference Upper-Air Network sites

Abstract. The potential for measurement redundancy to reduce uncertainty in atmospheric variables has not been investigated comprehensively for climate observations. We evaluated the usefulness of entropy and mutual correlation concepts, as defined in information theory, for quantifying random uncertainty and redundancy in time series of the integrated water vapour (IWV) and water vapour mixing ratio profiles provided by five highly instrumented GRUAN (GCOS, Global Climate Observing System, Reference Upper-Air Network) stations in 2010–2012. Results show that the random uncertainties on the IWV measured with radiosondes, global positioning system, microwave and infrared radiometers, and Raman lidar measurements differed by less than 8%. Comparisons of time series of IWV content from ground-based remote sensing instruments with in situ soundings showed that microwave radiometers have the highest redundancy with the IWV time series measured by radiosondes and therefore the highest potential to reduce the random uncertainty of the radiosondes time series. Moreover, the random uncertainty of a time series from one instrument can be reduced by ~ 60% by constraining the measurements with those from another instrument. The best reduction of random uncertainty is achieved by conditioning Raman lidar measurements with microwave radiometer measurements. Specific instruments are recommended for atmospheric water vapour measurements at GRUAN sites. This approach can be applied to the study of redundant measurements for other climate variables.

Water vapor turbulence profiles in stationary continental convective mixed layers

AbstractThe U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program's Raman lidar at the ARM Southern Great Plains site in north central Oklahoma has collected water vapor mixing ratio (q) profile data more than 90% of the time since October 2004. Three hundred (300) cases were identified where the convective boundary layer was quasi‐stationary and well mixed for a 2 h period, and q mean, variance, third‐order moment, and skewness profiles were derived from the 10 s, 75 m resolution data. These cases span the entire calendar year, and demonstrate that the q variance profiles at the mixed layer (ML) top changes seasonally and is strongly related to the gradient of q across the interfacial layer. The q variance at the top of the ML shows only weak correlations (r < 0.3) with sensible heat flux, Deardorff convective velocity scale, and turbulence kinetic energy measured at the surface. The median q skewness profile is most negative at 0.85 zi, zero at approximately zi, and positive above zi, where zi is the depth of the convective ML. The spread in the q skewness profiles is smallest between 0.95 zi and zi. The q skewness at altitudes between 0.6 zi and 1.2 zi is correlated with the magnitude of the q variance at zi, with increasingly negative values of skewness observed lower down in the ML as the variance at zi increases, suggesting that in cases with larger variance at zi there is deeper penetration of the warm, dry free tropospheric air into the ML.

Tropospheric water vapour and relative humidity profiles from lidar and microwave radiometry

Abstract. In this paper, we outline an iterative method to calibrate the water vapour mixing ratio profiles retrieved from Raman lidar measurements. Simultaneous and co-located radiosonde data are used for this purpose and the calibration results obtained during a radiosonde campaign in summer and autumn 2011 are presented. The water vapour profiles measured during night-time by the Raman lidar and radiosondes are compared and the differences between the methodologies are discussed. Then, a new approach to obtain relative humidity profiles by combination of simultaneous profiles of temperature (retrieved from a microwave radiometer) and water vapour mixing ratio (from a Raman lidar) is addressed. In the last part of this work, a statistical analysis of water vapour mixing ratio and relative humidity profiles obtained during 1 year of simultaneous measurements is presented.

The implementation of reverse Kessler warm rain scheme for radar reflectivity assimilation using a nudging approach in New Zealand

Reverse Kessler warm rain processes were implemented within the Weather Research and Forecasting Model (WRF) and coupled with a Newtonian relaxation, or nudging technique designed to improve quantitative precipitation forecasting (QPF) in New Zealand by making use of observed radar reflectivity and modest computing facilities. One of the reasons for developing such a scheme, rather than using 4D-Var for example, is that radar VAR scheme in general, and 4D-Var in particular, requires computational resources beyond the capability of most university groups and indeed some national forecasting centres of small countries like New Zealand. The new scheme adjusts the model water vapor mixing ratio profiles based on observed reflectivity at each time step within an assimilation time window. The whole scheme can be divided into following steps: (i) The radar reflectivity is firstly converted to rain water, and (ii) then the rain water is used to derive cloud water content according to the reverse Kessler scheme; (iii) The cloud water content associated water vapor mixing ratio is then calculated based on the saturation adjustment processes; (iv) Finally the adjusted water vapor is nudged into the model and the model background is updated. 13 rainfall cases which occurred in the summer of 2011/2012 in New Zealand were used to evaluate the new scheme, different forecast scores were calculated and showed that the new scheme was able to improve precipitation forecasts on average up to around 7 hours ahead depending on different verification thresholds.

Sensitivity of the regional climate model RegCM4.2 to planetary boundary layer parameterisation

This study investigates the performance of two planetary boundary layer (PBL) parameterisations in the regional climate model RegCM4.2 with specific focus on the recently implemented prognostic turbulent kinetic energy parameterisation scheme: the University of Washington (UW) scheme. When compared with the default Holtslag scheme, the UW scheme, in the 10-year experiments over the European domain, shows a substantial cooling. It reduces winter warm bias over the north-eastern Europe by 2 °C and reduces summer warm bias over central Europe by 3 °C. A part of the detected cooling is ascribed to a general reduction in lower tropospheric eddy heat diffusivity with the UW scheme. While differences in temperature tendency due to PBL schemes are mostly localized to the lower troposphere, the schemes show a much higher diversity in how vertical turbulent mixing of the water vapour mixing ratio is governed. Differences in the water vapour mixing ratio tendency due to the PBL scheme are present almost throughout the troposphere. However, they alone cannot explain the overall water vapour mixing ratio profiles, suggesting strong interaction between the PBL and other model parameterisations. An additional 18-member ensemble with the UW scheme is made, where two formulations of the master turbulent length scale in unstable conditions are tested and unconstrained parameters associated with (a) the evaporative enhancement of the cloud-top entrainment and (b) the formulation of the master turbulent length scale in stable conditions are systematically perturbed. These experiments suggest that the master turbulent length scale in the UW scheme could be further refined in the current implementation in the RegCM model. It was also found that the UW scheme is less sensitive to the variations of the other two selected unconstrained parameters, supporting the choice of these parameters in the default formulation of the UW scheme.

Water vapour mixing ratio profiles over Hornsund, Arctic. Intercomparison of lidar and AIRS results

Since October 2009, a ground-based Raman lidar system has been deployed to perform a regular, night-time, vertical sounding of a water vapour content in the lower and middle troposphere above Polish Polar Station at Hornsund (77.00°N, 15.55°E, 10 m a.s.l.) in the Arctic. The water vapour mixing ratio profiles were obtained for the atmosphere up to 6 km altitude, based on analysis of inelastic Raman backscattering signals from nitrogen molecules (at 387 nm) and water vapour particles (at 407 nm), calibrated with the data from a local Vaisala’s automatic meteorological station. The results obtained for winter seasons in the years 2009–2012 are in a good general agreement with the results obtained from the atmospheric infrared sounder (AIRS) on the Aqua satellite.

Comparison of IASI water vapour products over complex terrain with COPS campaign data

In this work, we compare IASI-retrieved vertical water vapour profiles and related precipitable water over a complex region, namely the Rhine Valley area, during the pre-operational period of IASI exploitation (June?August 2007). Both IASI water vapour mixing ratio profiles and integrated water vapour content are retrieved from L1C radiances spectra using two techniques and compared with water vapour related observations acquired during the Convective and Orographically-induced Precipitation Study (COPS) field campaign that took place in this area at that time (i.e. lidars, radiosoundings and a global positioning system - GPS - station network). This work addresses the issue of IASI vertical spatial resolution and its capability to detect two-layer water vapour structures such as those observed in a mountainous area and which play an important role in convective initiation or inhibition. We found that this capability mostly relies on the type of a-priori background vector (climatology or space-time colocated ECMWF analysis), which is used within the retrieval scheme. Systematic comparison of water vapour products derived from 71 IASI spectra confirms that IASI can retrieve water vapour amounts in 2 km width layers, in the lower troposphere, with an accuracy of approximately 10%.

Calibration and validation of water vapour lidar measurements from Eureka, Nunavut, using radiosondes and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer

Abstract. The Canadian Network for the Detection of Atmospheric Change and Environment Canada DIAL lidar located at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Nunavut, has been upgraded to measure water vapour mixing ratio profiles. The lidar is capable of measuring water vapour in the dry Arctic atmosphere up to the tropopause region. Measurements were obtained in the February to March polar sunrise during 2007, 2008 and 2009 as part of the Canadian Arctic ACE (Atmospheric Chemistry Experiment) Validation Campaign. Before such measurements can be used to address important questions in understanding dynamics and chemistry, the lidar measurements must be calibrated against an independent determination of water vapour. Here, radiosonde measurements of relative humidity have been used to empirically calibrate the lidar measurements. It was found that the calibration varied significantly between each year's campaign. However, the calibration of the lidar during an individual polar sunrise campaign agrees on average with the local radiosonde measurements to better than 12%. To independently validate the calibration of the lidar derived from the radiosondes, comparisons are made between the calibrated lidar measurements and water vapour measurements from the ACE satellite-borne Fourier Transform Spectrometer (ACE-FTS). The comparisons between the lidar and satellite-borne spectrometer for both a campaign average and single overpasses show favourable agreement between the two instruments and help validate the lidar's calibration. The 39 nights of high-Arctic water vapour measurements obtained offer the most detailed high spatial-temporal resolution measurement set available for understanding this time of transition from the long polar night to polar day.

RAMSES: German Meteorological Service autonomous Raman lidar for water vapor, temperature, aerosol, and cloud measurements

The Raman lidar for atmospheric moisture sensing (RAMSES) for unattended, continuous multiparameter atmospheric profiling is presented. A seeded frequency-tripled Nd:YAG laser serves as the light source. A nine-channel polychromator, nonfiber coupled to the main telescope (790mm diameter), is used for far-range measurements. Near-range observations are performed with a three-channel polychromator, fiber coupled to a secondary telescope (200mm diameter). Measurement parameters are water-vapor mixing ratio (MR), temperature, and the optical particle parameters, which are extinction coefficient, backscatter coefficient, lidar ratio, and depolarization ratio at 355nm. Profiles of water-vapor MR are measured from close to the surface up to 14km at night and 5km during the day under favorable atmospheric conditions in 20min. Temperature profiles of the troposphere and lower stratosphere are determined with the rotational-Raman technique. For the detection of the rotational Raman signals, a new beamsplitter/interference-filter experimental setup is implemented that is compact, robust, and easy to align. Furthermore, the polychromator design allows two independent methods for calibrating measurements of depolarization ratio. RAMSES optical design concept and experimental setup are detailed, and a description of the operational near-real-time data evaluation software is given. A multiday observation is discussed to illustrate the measurement capabilities of RAMSES.

Idealized Mesoscale Model Simulations of Open Cellular Convection Over the Sea

The atmospheric conditions during an observed case of open cellular convection over the North Sea were simulated using the Weather Research and Forecasting (WRF) numerical model. Wind, temperature and water vapour mixing ratio profiles from the WRF simulation were used to initialize an idealized version of the model, which excluded the effects of topography, surface inhomogeneities and large-scale weather forcing. Cells with an average diameter of 17.4 km developed. Simulations both with and without a capping inversion were made, and the cell-scale kinetic energy budget was calculated for each case. By considering all sources of explicit diffusion in the model, the budgets were balanced. In comparison with previous work based on observational studies, the use of three-dimensional, gridded model data afforded the possibility of calculating all terms in the budgets, which showed that the important terms in the budgets were buoyancy, pressure balance and inter-scale transfer to subgrid scales. Cells were also composited to calculate the average cell-scale flow and each of the budget terms on two-dimensional cross-sections through the cells, parallel and perpendicular to the mean wind direction.

Using Precipitation Observations in a Mesoscale Short-Range Ensemble Analysis and Forecasting System

Abstract A simple method to assimilate precipitation data from a synthesis of radar and gauge data is developed to operate alongside an ensemble Kalman filter that assimilates hourly surface observations. The mesoscale ensemble forecast system consists of 25 members with 30-km grid spacing and incorporates variability in both initial and boundary conditions and model physical process schemes. The precipitation assimilation method only incorporates information on when and where rainfall is observed. Model temperature and water vapor mixing ratio profiles at each grid point are modified if rainfall is observed but not predicted, or if rainfall is predicted but not observed. These modifications act to either increase or decrease, respectively, the likelihood that precipitation develops at that grid point. Two cases are examined in which this technique is applied to assimilate precipitation data every 15 min from 1200 to 1800 UTC, while hourly surface observations are also assimilated at the same time using the more sophisticated ensemble Kalman filter approach. Results show that the simple method for assimilating precipitation data helps the model develop precipitation where it is observed, resulting in the precipitation area being reproduced more accurately than in the run without precipitation-data assimilation, while not negatively influencing the positive results from the surface data assimilation. Improvement is also seen in the reliability of precipitation probabilities for a 1 mm h−1 threshold after the assimilation period, indicating that assimilating precipitation data may provide improved forecasts of the mesoscale environment for a few hours.

Wave–photochemistry coupling and its effect on water vapor, ozone and airglow variations in the atmosphere of Mars

A one-dimensional photochemical–transport model for the martian lower atmosphere has been developed to study the diurnal cycles of wave–photochemistry coupling. The model self-consistently calculates water vapor mixing ratio profiles, which exhibit strong vertical and diurnal variations mainly due to the high sensitivity of the saturation vapor pressure to temperature variation. The dynamical coupling of water vapor caused by the temperature variation induced by tidal waves, vertical transport parameterized by eddy diffusion, and linear relaxation introduced in condensation–sublimation processes all have similar timescales of diurnal variation. This leads to a significant asymmetric distribution of water vapor concentration as a function of local time. As a result, the net effect of the temperature variation by tidal waves depletes the water vapor concentration in its diurnal mean. The coupling processes also deplete the diurnally averaged HO x concentration, which in turn leads to significant enhancements of both ozone concentration and the associated airglow emissions in the martian atmosphere. The model also shows explicitly the importance of photochemical–transport coupling to the airglow emissions and its implications in species retrievals when the photochemical times of the excited states are comparable to the timescale of diurnal variation.