Final conference, Rome October 11, 2016 First measurements of the new 22 GHz water vapor spectrometer VESPA-22 obtained during the SVAAP campaign at Thule, Greenland Gabriele Mevi1,2, Giovanni Muscari1, Massimo Mari1, Daniela Meloni3, Tatiana Di Iorio3, Alcide di Sarra3, Giandomenico Pace3, Marco Cacciani4 1Istituto Nazionale di Geofisica e Vulcanologia, Italy, email: gabriele.mevi@ingv.it; 2Also at Mathematics and Physics Department, University of Roma Tre, Italy; 3Laboratory for Observations and Analyses of Earth and Climate, ENEA, Italy; 4Physics Department, University of Rome “La Sapienza”, Italy. Abstract Water vapor has a large impact on the Earth radiative budget, affecting both infrared and shortwave radiation. In the Arctic region, the importance of water vapor is enhanced by the so called Artic Amplification effect [Serreze and Francis, 2006], a positive feedback that links the quantity of water vapor in the troposphere, the presence of clouds, the ice coverage, and the surface temperature. Additionally, about 10% of the surface warming measured during the last two decades can be ascribed to stratospheric water vapor [Solomon et al., 2010]. The characterization of middle atmospheric water vapor profiles is also important to understand many chemical processes that occur in the Polar middle atmosphere, as water vapor is involved in the ozone chemistry. In order to identify and quantify the contribution of water vapor to the changes that are occurring in the Arctic, long-term measurements of tropospheric and stratospheric water vapor are necessary. With this purpose, during the SVAAP measurements campaign funded by the Italian PNRA (see the contribution by Meloni et al. to the ARCA conference) and in synergy with the ARCA project, a new 22 GHz spectrometer (the water Vapor Emission Spectrometer for Polar Atmospheres at 22 GHz, VESPA-22 [Bertagnolio et al., 2012]) was installed at Thule Air Base (76.5° N, 68.8° W), Greenland. VESPA-22 has been set-up for continuous unattended measurements. Since the early 90’s Thule Air Base has been hosting a NDACC (Network for the Detection of Atmospheric Composition Change) atmospheric observatory where instruments belonging to Italian (http://www.thuleatmos-it.it/), Danish and US research institutes and universities are installed to monitor the Arctic atmosphere and radiation budget. The SVAAP campaign took place in July 2016 and was mainly aimed at studying the role of water vapor and clouds in the radiation budget at the surface, which is also an important objective of the ARCA project. During the campaign we launched 23 radiosondes, carried out measurements of various atmospheric parameters (see contribution by Meloni et al.), and VESPA-22 operated side by side with the HATPRO microwave radiometer [Rose et al., 2006]. The campaign was characterized by ten days of fair weather followed by ten days of more unstable and cloudy conditions. VESPA-22 (figure 1) collects the microwave radiation emitted by the H2O rotational transition at 22.235 GHz with a spectral resolution of 31 kHz and a bandwidth of 500 MHz (figure 2). Using the relation between the emission line width and the atmospheric pressure, VESPA-22 spectral measurements can be inverted to obtain water vapor profiles from about 30 km up to 70 km with a vertical resolution of about 7 km and a temporal resolution of 1-2 profiles a day, depending on weather conditions (figure 3). The instrument can also retrieve the precipitable water vapor (PWV) by measuring the sky opacity 𝜏𝑧 with a temporal resolution of a few minutes and using the formula: PWV = aτz + bτzTatm + c (1) [Deuber et al., 2005] where 𝑇𝑎𝑡𝑚 is the mean tropospheric emission temperature calculated using radiosounding data, while a, b, and c are three site dependent coefficients. Equation 1 does not take