Cryogenic Frost Point Hygrometer Research Articles

Fluid dynamics analysis and experimental study for solar radiation error correction of sounding humidity sensor.

In order to correct the solar radiation error of relative humidity, the mainstream capacitive sounding humidity sensor HC103M2 is selected and investigated by simulation analysis and experimental verification. First, the basic theories for solar radiation error and sensor error itself are elaborated, and simulational and experimental platforms are introduced. The computational fluid dynamics (CFD) method is utilized to theoretically investigate the dry error of the humidity sensor caused by solar radiation heating, which is related to radiation intensity, altitude, and solar elevation angle as well as reflectivity, thickness, and shape of the shield. Then, in order to verify the accuracy of the simulation, an experimental platform including a humidity sensor and two temperature sensors to measure the solar radiation heating is built to analyze the relative error of humidity obtained by the CFD simulation and experiment. It is found that their maximum deviation is 3.30% and the average error is 1.94%, which indicates that the calculation using the CFD method is accurate and feasible. In order to easily and operationally predict the solar radiation heating of the humidity sensor, a back propagation (BP) neural network fusion algorithm based on three inputs of radiation intensity, air pressure, and solar elevation angle is proposed. Compared with the solar radiation heating obtained by CFD simulation, the maximum absolute error is about 0.2K, and the relative error of humidity is about ±1.30%. Finally, a case of vertical humidity profile correction considering the temperature-sensitive error of HC103M2 is analyzed. The response time of sensor measurement and the airflow into the shield are discussed as well. The corrected results after taking solar radiation heating into account are more similar to those measured by RS92 and cryogenic frost point hygrometer (CFH). This result shows that the prediction model is accurate, which may be applied to correct the dry error and further improve the accuracy of humidity measurement.

Unprecedented Observations of a Nascent In Situ Cirrus in the Tropical Tropopause Layer

AbstractA nascent in situ cirrus was observed on January 11, 2019 in the tropical tropopause layer (TTL) over the southwestern Indian Ocean, with the use of balloon‐borne instruments. Data from cryogenic frost point hygrometer (CFH) and Compact Optical Backscatter and AerosoL Detector (COBALD) instruments were used to characterize the cirrus and its environment. Optical modeling was employed to estimate the cirrus microphysical properties from the COBALD backscatter measurements. Newly fomed ice crystals with radius <1 μm and concentration ∼500 L−1 were reported at the tropopause. The relatively low concentration and CFH ice supersaturation (1.5) suggests a homogeneous freezing event stalled by a high‐frequency gravity wave. The observed vertical wind speed and temperature anomalies that triggered the cirrus formation were due to a 1.5‐km vertical‐scale wave, as shown by a spectral analysis. This cirrus observation shortly after nucleation is beyond remote sensing capabilities and presents a type of cirrus never reported before.

A powerful lidar system capable of 1 h measurements of water vapour in the troposphere and the lower stratosphere as well as the temperature in the upper stratosphere and mesosphere

Abstract. A high-power Raman lidar system has been installed at the high-altitude research station Schneefernerhaus (Garmisch-Partenkirchen, Germany) at 2675 ma.s.l., at the side of an existing wide-range differential absorption lidar (DIAL). An industrial XeCl laser was modified for linearly polarized single-line operation at an average power of about 180 W. This high power and a 1.5 m diameter receiver allow us to extend the operating range for water-vapour sounding to 20 km for a measurement time of just 1 h, at an uncertainty level of the mixing ratio of 1 to 2 ppm. This was achieved for a vertical resolution varied between just 0.2 and 0.6 km in the stratosphere. The lidar was successfully validated with a balloon-borne cryogenic frost-point hygrometer (CFH). In addition, temperature measurements up to altitudes of around 87 km were demonstrated for 1 h of signal averaging. The system has been calibrated with the DIAL, the CFH and radiosondes.

Effect of monsoon dynamics and deep convection on the upper troposphere lower stratosphere water vapour over Indian monsoon region

Balloon-borne cryogenic frost-point hygrometer (CFH) observations conducted over three stations Trivandrum, Hyderabad and Kolkata in the Indian region during the period 2014–2017 are used to study the influence of deep convection and monsoon dynamics on the distribution of water vapour in the upper troposphere and lower stratosphere (UTLS) and to quantify the amount of water vapour transported to the lower stratosphere (LS) during summer-monsoon (June to September). In summer monsoon season, CFH observations show a water vapour enhancement of ~40–250% in the upper troposphere (UT) and 0.5–1 ppmv (10–40%) in the LS compared to pre-monsoon. In this season, the spatial pattern of Microwave Limb Sounder (MLS) derived water vapour mixing ratio (WVMR) at 100 hPa peaks north of the deep convection core over the head Bay of Bengal (BoB). In the LS, the water vapour maximum shows a south westward shift with altitude in accordance with the anticyclonic circulation flow. The maximum altitude of deep convective cloud top increases north eastward in accordance with the peak in tropical easterly jet (TEJ) causing the altitudinal shift in water vapour enhancement in the UT. The probability of dehydration (WVMR<3 ppmv) maximizes west of the deep convective core over Head BoB. During summer-monsoon, the day-to-day variability of water vapour in the tropical tropopause layer (TTL) is mainly controlled by the dehydration of air due to freeze drying (temperature dependent) and rehydration due to recurrent overshooting deep convections. Direct injection of water vapour into the LS region is probable when the tropopause is relatively warm (>192 K).

Effect of deep convection on the tropical tropopause layer composition over the southwest Indian Ocean during austral summer

Abstract. Balloon-borne measurements of cryogenic frost-point hygrometer (CFH) water vapor, ozone and temperature and water vapor lidar measurements from the Maïdo Observatory on Réunion Island in the southwest Indian Ocean (SWIO) were used to study tropical cyclones' influence on tropical tropopause layer (TTL) composition. The balloon launches were specifically planned using a Lagrangian model and Meteosat-7 infrared images to sample the convective outflow from tropical storm (TS) Corentin on 25 January 2016 and tropical cyclone (TC) Enawo on 3 March 2017. Comparing the CFH profile to Aura's Microwave Limb Sounder's (MLS) monthly climatologies, water vapor anomalies were identified. Positive anomalies of water vapor and temperature, and negative anomalies of ozone between 12 and 15 km in altitude (247 to 121 hPa), originated from convectively active regions of TS Corentin and TC Enawo 1 d before the planned balloon launches according to the Lagrangian trajectories. Near the tropopause region, air masses on 25 January 2016 were anomalously dry around 100 hPa and were traced back to TS Corentin's active convective region where cirrus clouds and deep convective clouds may have dried the layer. An anomalously wet layer around 68 hPa was traced back to the southeast Indian Ocean where a monthly water vapor anomaly of 0.5 ppmv was observed. In contrast, no water vapor anomaly was found near or above the tropopause region on 3 March 2017 over Maïdo as the tropopause region was not downwind of TC Enawo. This study compares and contrasts the impact of two tropical cyclones on the humidification of the TTL over the SWIO. It also demonstrates the need for accurate balloon-borne measurements of water vapor, ozone and aerosols in regions where TTL in situ observations are sparse.

Validation of the Water Vapor Profiles of the Raman Lidar at the Maïdo Observatory (Reunion Island) Calibrated with Global Navigation Satellite System Integrated Water Vapor

The Maïdo high-altitude observatory located in Reunion Island (21 ∘ S, 55.5 ∘ E) is equipped with the Lidar1200, an innovative Raman lidar designed to measure the water vapor mixing ratio in the troposphere and the lower stratosphere, to perform long-term survey and processes studies in the vicinity of the tropopause. The calibration methodology is based on a GNSS (Global Navigation Satellite System) IWV (Integrated Water Vapor) dataset. The lidar water vapor measurements from November 2013 to October 2015 have been calibrated according to this methodology and used to evaluate the performance of the lidar. The 2-year operation shows that the calibration uncertainty using the GNSS technique is in good agreement with the calibration derived using radiosondes. During the MORGANE (Maïdo ObservatoRy Gaz and Aerosols NDACC Experiment) campaign (Reunion Island, May 2015), CFH (Cryogenic Frost point Hygrometer) radiosonde and Raman lidar profiles are compared and show good agreement up to 22 km asl; no significant biases are detected and mean differences are smaller than 9% up to 22 km asl.

Comparison of the GRUAN data products for Meisei RS-11G and Vaisala RS92-SGP radiosondes at Tateno (36.06° N, 140.13° E), Japan

Abstract. A total of 87 dual flights of Meisei RS-11G radiosondes and Vaisala RS92-SGP radiosondes were carried out at the Aerological Observatory of the Japan Meteorological Agency (36.06∘ N, 140.13∘ E, 25.2 m) from April 2015 to June 2017. Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) data products from both sets of radiosonde data for 52 flights were subsequently created using a documented processing program along with the provision of optimal estimates for measurement uncertainty. Differences in the performance of the radiosondes were then quantified using the GRUAN data products. The temperature measurements of RS-11G were, on average, 0.4 K lower than those of RS92-SGP in the stratosphere for daytime observations. The relative humidity measurements of RS-11G were, on average, 2 % RH (relative humidity) lower than those of RS92-SGP under 90 % RH–100 % RH conditions, while RS-11G gave on average 5 % RH higher values than RS92-SGP under ≤50 % RH conditions. The results from a dual flight of RS-11G and a cryogenic frost point hygrometer (CFH) also showed that RS-11G gave 1 % RH–10 % RH higher values than the CFH in the troposphere. Differences between the RS-11G and RS92-SGP temperature and relative humidity measurements, based on combined uncertainties, were also investigated to clarify major influences behind the differences. It was found that temperature differences in the stratosphere during daytime observation were within the range of uncertainty (k=2), and that sensor orientation is the major source of uncertainty in the RS92-SGP temperature measurement, while sensor albedo is the major source of uncertainty for RS-11G. The relative humidity difference in the troposphere was larger than the uncertainty (k=2) after the radiosondes had passed through the cloud layer, and the temperature–humidity dependence correction was the major source of uncertainty in RS-11G relative humidity measurement. Uncertainties for all soundings were also statistically investigated. Most nighttime temperature measurements for pressures of &gt;10 hPa were in agreement, while relative humidity in the middle troposphere exhibited significant differences. Around half of all daytime temperature measurements at pressures of ≤150 hPa and relative humidity measurements around the 500 hPa level were not in agreement.

Intercomparison of Cryogenic Frost-Point Hygrometer Observations With Radiosonde, SAPHIR, MLS, and Reanalysis Datasets Over Indian Peninsula

This paper assesses the performance of water vapor measurements by Sondeur Atmospherique du Profild’ Humidite Intertropicale par Radiometrie (SAPHIR), microwave limb sounder (MLS), and the global reanalysis water vapor data [Modern Era Retrospective analysis for Research and Applications (MERRA) and European Center for Medium-Range Weather Forecasts reanalysis (ERA) interim] by comparing with water vapor-measured in situ by cryogenic frost-point hygrometer (CFH) at two tropical stations, Trivandrum (8.5°N, 76.9°E) and Hyderabad (17.47°N, 78.58°E). The iMet-1 radiosonde though overestimates frost-point temperature (3%–5%) in the 4–10-km altitude region with respect to CFH, it agrees well with CFH observations in the upper troposphere and the lower troposphere with a mean difference <2% and ~1%, respectively. SAPHIR–CFH intercomparison is done for the troposphere region, and MLS, MERRA, and ERA interim are compared with CFH in the lower stratosphere region. SAPHIR and CFH comparison shows a reasonable agreement between both the datasets with a relative humidity difference of about 15% in the lower and middle troposphere and a dry bias of ~40% in the upper troposphere. Intercomparison between CFH and MLS water vapor mixing ratios (WVMRs) shows a small wet bias (−10% to −20%) for the MLS in the lower stratospheric region between 100 and 50 hPa and a small dry bias (<10%) above that region. This paper shows that the MLS always underestimates when the CFH WVMR is greater than 6 ppmv and overestimates when the WVMR is less than 2 ppmv. The intercomparison of CFH with MERRA and ERA interim specific humidity shows results similar to that with MLS.

Two-year operation of the lidar1200: from fine-scale tropospheric structures to lower stratospheric water vapor detection

The 2-year lidar water vapor database (November 2013 - October 2015) of the Maïdo Observatory (Reunion Island / 21°S,55.5°E) is now processed. The performances of the lidar in providing accurate vertical structures are shown to be good. The ability to measure quantities of a few ppmv in the lower stratosphere is demonstrated (based on Cryogenic Frost point Hygrometer sonde/lidar profiles comparisons) for a 48-hour integration time period, up to 22 km (with a vertical resolution of 1.3 km).

An update on the uncertainties of water vapor measurements using cryogenic frost point hygrometers

Abstract. Long time series of observations of essential climate variables in the troposphere and stratosphere are often impacted by inconsistencies in instrumentation and ambiguities in the interpretation of the data. To reduce these problems of long-term data series, all measurements should include an estimate of their uncertainty and a description of their sources. Here we present an update of the uncertainties for tropospheric and stratospheric water vapor observations using the cryogenic frost point hygrometer (CFH). The largest source of measurement uncertainty is the controller stability, which is discussed here in detail. We describe a method to quantify this uncertainty for each profile based on the measurements. We also show the importance of a manufacturer-independent ground check, which is an essential tool to continuously monitor the uncertainty introduced by instrument variability. A small bias, which has previously been indicated in lower tropospheric measurements, is described here in detail and has been rectified. Under good conditions, the total from all sources of uncertainty of frost point or dew point measurements using the CFH can be better than 0.2 K. Systematic errors, which are most likely to impact long-term climate series, are verified to be less than 0.1 K. The impact of the radiosonde pressure uncertainty on the mixing ratio for properly processed radiosondes is considered small. The mixing ratio uncertainty may be as low as 2 to 3 %. The impact of the ambient temperature uncertainty on relative humidity (RH) is generally larger than that of the frost point uncertainty. The relative RH uncertainty may be as low as 2 % in the lower troposphere and 5 % in the tropical tropopause region.

Balloon-borne cryogenic frost-point hygrometer observations of water vapour in the tropical upper troposphere and lower stratosphere over India: First results

Balloon-borne cryogenic frost-point hygrometer (CFH) observations of water vapour in the upper troposphere and lower stratosphere (UTLS) region carried out over India, from Trivandrum [8.5°N, 76.9°E] and Hyderabad [17.5°N, 78.6°E], were compared with that obtained from quasi-collocated Aura-Microwave Limb Sounder (MLS) satellite observations. Comparisons show a small dry bias for MLS in the stratosphere. Saturated or super-saturation layers observed near the base of tropical tropopause layer (TTL) are consistent with the quasi-collocated space-based observations of tropical cirrus from KALPANA-1 and CALIPSO. Disturbance of large scale waves in the upper troposphere appears to modulate the water vapour and cirrus distribution.

Advancements, measurement uncertainties, and recent comparisons of the NOAA frost point hygrometer.

The NOAA frost point hygrometer (FPH) is a balloon-borne instrument flown monthly at three sites to measure water vapor profiles up to 28 km. The FPH record from Boulder, Colorado, is the longest continuous stratospheric water vapor record. The instrument has an uncertainty in the stratosphere that is < 6 % and up to 12 % in the troposphere. A digital microcontroller version of the instrument improved upon the older versions in 2008 with sunlight filtering, better frost control, and resistance to radio frequency interference (RFI). A new thermistor calibration technique was implemented in 2014, decreasing the uncertainty in the thermistor calibration fit to less than 0.01 °C over the full range of frost – or dew point temperatures (−93 to +20 °C) measured during a profile. Results from multiple water vapor intercomparisons are presented, including the excellent agreement between the NOAA FPH and the direct tunable diode laser absorption spectrometer (dTDLAS) MC-PicT-1.4 during AquaVIT-2 chamber experiments over 6 days that provides confidence in the accuracy of the FPH measurements. Dual instrument flights with two FPHs or an FPH and a cryogenic frost point hygrometer (CFH) also show good agreement when launched on the same balloon. The results from these comparisons demonstrate the high level of accuracy of the NOAA FPH.

Balloon-borne observations of lower stratospheric water vapor at Syowa Station, Antarctica in 2013

Balloon-borne observations of lower stratospheric water vapor were conducted with the Cryogenic Frostpoint Hygrometer (CFH) in July, September, and November 2013 at Syowa Station (69.0oS, 39.6oE) in the Antarctic. High-precision and high vertical resolution data of water vapor concentration up to an altitude of about 28 km were obtained successfully except for a contamination in the observation of July 2013. A comparison between the CFH and coincident satellite (i.e., Aura/MLS) observations showed a good agreement within their uncertainty. A position of Syowa Station relative to the stratospheric polar vortex edge varied depending on both the observation date and altitude. Temperature and pressure histories of the observed air parcels were examined by 10-day backward trajectories. These analyses clearly demonstrated that most air parcels observed in the lower stratosphere above Syowa Station experienced final dehydration inside the polar vortex. On the other hand, a clear signature of rehydration or incomplete dehydration was also observed around a 25 hPa pressure level in the observation of July 2013.

Validation of Aura Microwave Limb Sounder water vapor and ozone profiles over the Tibetan Plateau and its adjacent region during boreal summer

We present validation studies of MLS V2.2 and V3.3 water vapor (WV) and ozone profiles over the Tibetan Plateau (Naqu and Lhasa) and its adjacent region (Tengchong) respectively by using the balloon-borne Cryogenic Frost point Hygrometer and Electrochemical Concentration Cell ozonesonde. Coincident in situ measurements were selected to compare the MLS V2.2 and V3.3 WV and ozone profiles for understanding the applicability of the two version MLS products over the region. MLS V2.2 and V3.3 WV profiles respectively show their differences within −2.2±15.7% (n=74) and 0.3±14.9% (n=75) in the stratosphere at and above 82.5 hPa. Accordingly, at 100 hPa, the altitude approaching the tropopuase height, differences are within 9.8±46.0% (n=18) and 23.0±45.8% (n=17), and they are within 21.5±90.6% (n=104) and 6.0±83.4% (n=99) in upper troposphere. The differences of MLS ozone are within −11.7±16.3% (n=135, V2.2) and 15.6±24.2% (n=305, V3.3) at and above 82.5 hPa. At 100 hPa, they are within −3.5±54.4% (n=27) and −8.7±41.6% (n=38), and within 18.0±79.1% (n=47) and 34.2±76.6% (n=160) in the upper troposphere. The relative difference of MLS WV and ozone profile has significant oscillation and scatter at upper troposphere and lower stratosphere partly due to the stronger gradients of WV and ozone concentrations here as well the linear interpolation of sonde data for the intercomparison. At and below 70 hPa, the relative differences of MLS ozone are significantly larger over Lhasa during the Tibetan Plateau “ozone valley” season, which is also the Asian Summer Monsoon period. The MLS ozone differences over the three sites are similar in their vertical distributions during that period. A simple linear correlation analysis between MLS and sonde profiles indicates that the sensitivity of MLS profile products is related to concentrations at each pressure level. The MLS V3.3 product sensitivity is slightly improved for WV at and above 82.5 hPa, whereas it is not obvious for ozone. The possible factors contributing to the differences of the MLS profile products of WV and ozone are discussed.

Arctic stratospheric dehydration – Part 1: Unprecedented observation of vertical redistribution of water

Abstract. We present high-resolution measurements of water vapour, aerosols and clouds in the Arctic stratosphere in January and February 2010 carried out by in situ instrumentation on balloon sondes and high-altitude aircraft combined with satellite observations. The measurements provide unparalleled evidence of dehydration and rehydration due to gravitational settling of ice particles. An extreme cooling of the Arctic stratospheric vortex during the second half of January 2010 resulted in a rare synoptic-scale outbreak of ice polar stratospheric clouds (PSCs) remotely detected by the lidar aboard the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) satellite. The widespread occurrence of ice clouds was followed by sedimentation and consequent sublimation of ice particles, leading to vertical redistribution of water inside the vortex. A sequence of balloon and aircraft soundings with chilled mirror and Lyman- α hygrometers (Cryogenic Frostpoint Hygrometer, CFH; Fast In Situ Stratospheric Hygrometer, FISH; Fluorescent Airborne Stratospheric Hygrometer, FLASH) and backscatter sondes (Compact Optical Backscatter Aerosol Detector, COBALD) conducted in January 2010 within the LAPBIAT (Lapland Atmosphere-Biosphere Facility) and RECONCILE (Reconciliation of Essential Process Parameters for an Enhanced Predictability of Arctic Stratospheric Ozone Loss and its Climate Interactions) campaigns captured various phases of this phenomenon: ice formation, irreversible dehydration and rehydration. Consistent observations of water vapour by these independent measurement techniques show clear signatures of irreversible dehydration of the vortex air by up to 1.6 ppmv in the 20–24 km altitude range and rehydration by up to 0.9 ppmv in a 1 km thick layer below. Comparison with space-borne Aura MLS (Microwave Limb Sounder) water vapour observations allow the spatiotemporal evolution of dehydrated air masses within the Arctic vortex to be derived and upscaled.

Upward mass fluxes in tropical upper troposphere and lower stratosphere derived from radiative transfer calculations

Yang et al. [1] quantified vertical velocity and upward mass fluxes in tropical lower stratosphere based on radiative heating rate calculations using the Fu-Liou radiation model along with 8-year Southern Hemisphere Additional Ozonesondes balloon-borne measurements of temperature and ozone and cryogenic frost-point hygrometer measured water vapor. The impact of tropospheric clouds on stratospheric heating rates was considered using cloud distributions from the International Satellite Cloud Climatology Project. Since the radiative heating rate in the lower stratosphere can be as small as 0.1–0.2K/day, an accurate radiative heating rate calculation including all radiatively active species is required. In this paper, we revisit the calculations in Yang et al. [1] by developing a line-by-line radiative transfer model (LBLRTM-D4S) for multiple scattering atmospheres. We consider the cloud impact using the cloud fields based on active lidar and radar observations from CALIPSO and CloudSat so that the quantification of upward mass fluxes in tropical lower stratosphere can be extended to tropical upper troposphere. The annual mean mass fluxes and vertical velocities from LBLRTM-D4S are ∼14kgm−2 day−1 and 0.77mms−1, respectively, at 120hPa (15.5km), and ∼1.2kgm−2 day−1 and 0.13mms−1 at 60hPa (19.5km). We examine the accuracy of three commonly used efficient radiation models including Fu-Liou, RRTM, and SBDART in estimating tropical upward mass fluxes against the LBLRTM-D4S results.

Particle backscatter and relative humidity measured across cirrus clouds and comparison with microphysical cirrus modelling

Abstract. Advanced measurement and modelling techniques are employed to estimate the partitioning of atmospheric water between the gas phase and the condensed phase in and around cirrus clouds, and thus to identify in-cloud and out-of-cloud supersaturations with respect to ice. In November 2008 the newly developed balloon-borne backscatter sonde COBALD (Compact Optical Backscatter and AerosoL Detector) was flown 14 times together with a CFH (Cryogenic Frost point Hygrometer) from Lindenberg, Germany (52° N, 14° E). The case discussed here in detail shows two cirrus layers with in-cloud relative humidities with respect to ice between 50% and 130%. Global operational analysis data of ECMWF (roughly 1° × 1° horizontal and 1 km vertical resolution, 6-hourly stored fields) fail to represent ice water contents and relative humidities. Conversely, regional COSMO-7 forecasts (6.6 km × 6.6 km, 5-min stored fields) capture the measured humidities and cloud positions remarkably well. The main difference between ECMWF and COSMO data is the resolution of small-scale vertical features responsible for cirrus formation. Nevertheless, ice water contents in COSMO-7 are still off by factors 2–10, likely reflecting limitations in COSMO's ice phase bulk scheme. Significant improvements can be achieved by comprehensive size-resolved microphysical and optical modelling along backward trajectories based on COSMO-7 wind and temperature fields, which allow accurate computation of humidities, homogeneous ice nucleation, resulting ice particle size distributions and backscatter ratios at the COBALD wavelengths. However, only by superimposing small-scale temperature fluctuations, which remain unresolved by the numerical weather prediction models, can we obtain a satisfying agreement with the observations and reconcile the measured in-cloud non-equilibrium humidities with conventional ice cloud microphysics. Conversely, the model-data comparison provides no evidence that additional changes to ice-cloud microphysics – such as heterogeneous nucleation or changing the water vapour accommodation coefficient on ice – are required.

Development of cloud detection methods using CFH, GTS1, and RS80 radiosondes

The accuracies of three instruments in measuring atmospheric column humidity were assessed during an upper troposphere and lower stratosphere observation campaign conducted from 7 to 13 August 2009 in Kunming, China. The three instruments are a cryogenic frost-point hygrometer (CFH), a Vaisala RS80 radiosonde (RS80), and a GTS1 radiosonde (GTS1). The accuracy of relative humidity (RH) measurements made by the CFH, GTS1, and RS80 was similar between the surface and 500 hPa (∼5.5 km above sea level). However, above 500 hPa, the errors in RH measurements made by the RS80, relative to measurements made by the CFH, are much less than those detected with the GTS1. Three different retrieval methods for determining cloud boundaries from CFH, RS80, and GTS1 measurements were developed and take into account the differences in accuracy among the three instruments. The method for the CFH is based on RH thresholds at all levels, which demands high accuracy. Given that the accuracy of RH measurements decreases at higher altitudes, the cloud detection methods for RS80 and GTS1 are different for different altitude ranges. Below 5 km, the methods for the RS80 and the GTS1 are similar to that of the CFH; above 5 km, the methods for the RS80 and the GTS1 are both developed based on the second-order derivatives of temperature and RH with respect to height, but with different criteria applied. Comparisons of cloud-layer retrievals derived from the three measurements are also made.

Ground-based water vapor raman lidar measurements up to the upper troposphere and lower stratosphere for long-term monitoring

Abstract. Recognizing the importance of water vapor in the upper troposphere and lower stratosphere (UTLS) and the scarcity of high-quality, long-term measurements, JPL began the development of a powerful Raman lidar in 2005 to try to meet these needs. This development was endorsed by the Network for the Detection of Atmospheric Composition Change (NDACC) and the validation program for the EOS-Aura satellite. In this paper we review the stages in the instrumental development, data acquisition and analysis, profile retrieval and calibration procedures of the lidar, as well as selected results from three validation campaigns: MOHAVE (Measurements of Humidity in the Atmosphere and Validation Experiments), MOHAVE-II, and MOHAVE 2009. In particular, one critical result from this latest campaign is the very good agreement (well below the reported uncertainties) observed between the lidar and the Cryogenic Frost-Point Hygrometer in the entire lidar range 3–20 km, with a mean bias not exceeding 2% (lidar dry) in the lower troposphere, and 3% (lidar moist) in the UTLS. Ultimately the lidar has demonstrated capability to measure water vapor profiles from ∼1 km above the ground to the lower stratosphere with a precision of 10% or better near 13 km and below, and an estimated accuracy of 5%. Since 2005, nearly 1000 profiles have been routinely measured, and since 2009, the profiles have typically reached 14 km for one-hour integration times and 1.5 km vertical resolution, and can reach 21 km for 6-h integration times using degraded vertical resolutions. These performance figures show that, with our present target of routinely running our lidar two hours per night, 4 nights per week, we can achieve measurements with a precision in the UTLS equivalent to that achieved if launching one CFH per month.

Matching radiative transfer models and radiosonde data from the EPS/Metop Sodankylä campaign to IASI measurements

Abstract. Radiances observed from IASI are compared to calculated ones. Calculated radiances are obtained using several radiative transfer models (OSS, LBLRTM v11.3 and v11.6) on best estimates of the atmospheric state vectors. The atmospheric state vectors are derived from cryogenic frost point hygrometer and humidity dry bias corrected RS92 measurements flown on sondes launched 1 h and 5 min before IASI overpass time. The temperature and humidity best estimate profiles are obtained by interpolating or extrapolating these measurements to IASI overpass time. The IASI observed and calculated radiances match to within one sigma IASI instrument noise in the spectral region where water vapour is a strong absorber (wavenumber, ν, in the range of 1500 ≤ ν ≤ 1570 and 1615 ≤ ν ≤ 1800 cm−1).