A 10‐year integrated atmospheric water vapor record using precision filter radiometers at two high‐alpine sites

Nyeki, S.; Vuilleumier, Laurent; Morland, June; Bokoye, Amadou I.; Viatte, P.; Mätzler, Christian; Kämpfer, Niklaus

doi:10.1029/2005gl024079

Cited by 15 publications

(27 citation statements)

References 13 publications

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“…This introduces a negative fair weather bias in the IWV data, since cloudy conditions are often associated with higher IWV values. Nyeki et al (2005) found a small dry bias of 0.4 mm of a precision filter radiometer (sun photometer) with respect to a GPS receiver at Davos in Switzerland.…”

Section: Sun Photometermentioning

confidence: 99%

Tropospheric water vapour above Switzerland over the last 12 years

Morland

Coen²,

Hocke

et al. 2009

Atmos. Chem. Phys.

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Abstract. Integrated Water vapour (IWV) has been measured since 1994 by the TROWARA microwave radiometer in Bern, Switzerland. Homogenization techniques were used to identify and correct step changes in IWV related to instrument problems. IWV from radiosonde, GPS and sun photometer (SPM) was used in the homogenisation process as well as partial IWV columns between valley and mountain weather stations. The average IWV of the homogenised TROWARA time series was 14.4 mm over the 1996-2007 period, with maximum and minimum monthly average values of 22.4 mm and 8 mm occurring in August and January, respectively. A weak diurnal cycle in TROWARA IWV was detected with an amplitude of 0.32 mm, a maximum at 21:00 UT and a minimum at 11:00 UT. For 1996-2007, TROWARA trends were compared with those calculated from the Payerne radiosonde and the closest ECMWF grid point to Bern. Using least squares analysis, the IWV time series of radiosondes at Payerne, ECMWF, and TROWARA showed consistent positive trends from 1996 to 2007. The radiosondes measured an IWV trend of 0.45±0.29%/y, the TROWARA radiometer observed a trend of 0.39±0.44%/y, and ECMWF operational analysis gave a trend of 0.25±0.34%/y. Since IWV has a strong and variable annual cycle, a seasonal trend analysis (Mann-Kendall analysis) was also performed. The seasonal trends are stronger by a factor 10 or so compared to the full year trends above. The positive IWV trends of the summer months are partly compensated by the negative trends of the winter months. The strong seasonal trends of IWV on regional scale underline the necessity of long-term monitoring of IWV for detection,understanding, and forecast of climate change effects in the Alpine region.

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Section: Sun Photometermentioning

confidence: 99%

Tropospheric water vapour above Switzerland over the last 12 years

Morland

Coen²,

Hocke

et al. 2009

Atmos. Chem. Phys.

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“…Measurements are made in sunny conditions at time intervals of between 30 s and 2 min (depending on the station), and are averaged over hourly periods before being stored in the database. Continuous sun photometer measurements began at Davos in 1995 (Nyeki et al, 2005), at Jungfraujoch in 1999, at Locarno in 2001 and at Payerne in 2002. Since the CHARM network also measures global solar irradiance and infrared (long-wave) irradiance from the atmosphere, it provides the opportunity for linking IWV observations to changes in atmospheric radiation.…”

Section: Sun Photometer/precision Filter Radiometer Measurementsmentioning

confidence: 99%

The STARTWAVE atmospheric water database

et al. 2006

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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. • 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 caCorrespondence to: J. Morland (june.morland@mw.iap.unibe.ch) pabilites 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.

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“…Finally, the relatively low cost and easy deployment of sun photometers allowed the establishment of several international networks in the last 30 years worldwide. AErosol RObotic NETwork (AERONET) network (Holben et al, 1998;Smirnov et al, 2004), Global Atmospheric Watching Precision Filter Radiometer (GAW-PFR) network (Wehrli, 2000;Nyeki et al, 2005) and European Skynet Radiometers (ESR-SKYNET) network (Campanelli et al, 2012(Campanelli et al, , 2014 provide operationally free estimation of W or develop algorithms and open-source packages for improving the retrieval of this important atmospheric pa- rameter. However, the great problem of this methodology is the estimation of the sun-photometric calibration parameters.…”

mentioning

confidence: 99%

Precipitable water vapour content from ESR/SKYNET sun–sky radiometers: validation against GNSS/GPS and AERONET over three different sites in Europe

et al. 2018

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Abstract. The estimation of the precipitable water vapour content (W ) with high temporal and spatial resolution is of great interest to both meteorological and climatological studies. Several methodologies based on remote sensing techniques have been recently developed in order to obtain accurate and frequent measurements of this atmospheric parameter. Among them, the relative low cost and easy deployment of sun-sky radiometers, or sun photometers, operating in several international networks, allowed the development of automatic estimations of W from these instruments with high temporal resolution. However, the great problem of this methodology is the estimation of the sun-photometric calibration parameters. The objective of this paper is to validate a new methodology based on the hypothesis that the calibration parameters characterizing the atmospheric transmittance at 940 nm are dependent on vertical profiles of temperature, air pressure and moisture typical of each measurement site. To obtain the calibration parameters some simultaneously seasonal measurements of W , from independent sources, taken over a large range of solar zenith angle and covering a wide range of W , are needed. In this work yearly GNSS/GPS datasets were used for obtaining a table of photometric calibration constants and the methodology was applied and validated in three European ESR-SKYNET network sites, characterized by different atmospheric and climatic conditions: Rome, Valencia and Aosta. Results were validated against the GNSS/GPS and AErosol RObotic NETwork (AERONET) W estimations. In both the validations the agreement was very high, with a percentage RMSD of about 6, 13 and 8 % in the case of GPS intercomparison at Rome, Aosta and Valencia, respectively, and of 8 % in the case of AERONET comparison in Valencia.Analysing the results by W classes, the present methodology was found to clearly improve W estimation at low W content when compared against AERONET in terms of % bias, bringing the agreement with the GPS (considered the reference one) from a % bias of 5.76 to 0.52.

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A 10‐year integrated atmospheric water vapor record using precision filter radiometers at two high‐alpine sites

Cited by 15 publications

References 13 publications

Tropospheric water vapour above Switzerland over the last 12 years

Tropospheric water vapour above Switzerland over the last 12 years

The STARTWAVE atmospheric water database

Precipitable water vapour content from ESR/SKYNET sun–sky radiometers: validation against GNSS/GPS and AERONET over three different sites in Europe

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