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Atmos. Meas. Tech., 11, 1099-1117, 2018
https://doi.org/10.5194/amt-11-1099-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
23 Feb 2018
VESPA-22: a ground-based microwave spectrometer for long-term measurements of polar stratospheric water vapor
Gabriele Mevi1,2, Giovanni Muscari1, Pietro Paolo Bertagnolio1,a, Irene Fiorucci1,b, and Giandomenico Pace3 1Istituto Nazionale di Geofisica e Vulcanologia, Rome, 00143, Italy
2Mathematics and Physics Department, Roma Tre University, Rome, 00146, Italy
3ENEA, Laboratory for Observations and Analyses of Earth and Climate, Rome, 00123, Italy
anow at: AECOM, Croydon, CRO 2AP, UK
bnow at: Istituto Paritario Vincenzo Pallotti, Rome, 00122, Italy
Abstract. The new ground-based 22 GHz spectrometer, VESPA-22 (water Vapor Emission Spectrometer for Polar Atmosphere at 22 GHz) measures the 22.23 GHz water vapor emission line with a bandwidth of 500 MHz and a frequency resolution of 31 kHz. The integration time for a measurement ranges from 6 to 24 h, depending on season and weather conditions. Water vapor spectra are collected using the beam-switching technique. VESPA-22 is designed to operate automatically with little maintenance; it employs an uncooled front-end characterized by a receiver temperature of about 180 K and its quasi-optical system presents a full width at half maximum of 3.5°. Every 30 min VESPA-22 measures also the sky opacity using the tipping curve technique. The instrument calibration is performed automatically by a noise diode; the emission temperature of this element is estimated twice an hour by observing alternatively a black body at ambient temperature and the sky at an elevation of 60°. The retrieved profiles obtained inverting 24 h integration spectra present a sensitivity larger than 0.8 from about 25 to 75 km of altitude during winter and from about 30 to 65 km during summer, a vertical resolution from about 12 to 23 km (depending on altitude), and an overall 1σ uncertainty lower than 7 % up to 60 km altitude and rapidly increasing to 20 % at 75 km.

In July 2016, VESPA-22 was installed at the Thule High Arctic Atmospheric Observatory located at Thule Air Base (76.5° N, 68.8° W), Greenland, and it has been operating almost continuously since then. The VESPA-22 water vapor mixing ratio vertical profiles discussed in this work are obtained from 24 h averaged spectra and are compared with version 4.2 of concurrent Aura/Microwave Limb Sounder (MLS) water vapor vertical profiles. In the sensitivity range of VESPA-22 retrievals, the intercomparison from July 2016 to July 2017 between VESPA-22 dataset and Aura/MLS dataset convolved with VESPA-22 averaging kernels shows an average difference within 1.4 % up to 60 km altitude and increasing to about 6 % (0.2 ppmv) at 72 km.

Citation: Mevi, G., Muscari, G., Bertagnolio, P. P., Fiorucci, I., and Pace, G.: VESPA-22: a ground-based microwave spectrometer for long-term measurements of polar stratospheric water vapor, Atmos. Meas. Tech., 11, 1099-1117, https://doi.org/10.5194/amt-11-1099-2018, 2018.
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Short summary
In July 2016, a new ground-based 22 GHz spectrometer for measuring lower and middle atmospheric water vapor was installed at the Thule High Arctic Atmospheric Observatory located at Thule Air Base (76.5° N, 68.8° W), Greenland. The spectrometer, VESPA-22, is designed to operate automatically with little maintenance. The intercomparison between VESPA-22 dataset and the satellite-based Microwave Limb Sounder dataset shows an average difference within 1.4 % up to 60 km altitude.
In July 2016, a new ground-based 22 GHz spectrometer for measuring lower and middle atmospheric...
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