Description: In the frame of the OASIS-YOPP project measurements of Integrated Water Vapor (IWV) and Temperature Profile (TP) have been carried out at the Thule High Arctic Atmospheric Observatory (THAAO, http://www.thuleatmos-it.it/) for the winter Arctic Special Observing Period of the YOPP (February 1st to March 31st 2018). The Observatory is located at South Mountain at 220 m a.s.l. in proximity of the Thule Air Base (76.5 °N, 68.8° W). IWV and TP are retrieved respectively from the 14 brightness temperatures (BTs) measured by a RPG HATPRO-G2 microwave radiometer (MWR) in the K and the V band (Rose, T., Crewell, S., and Löhnert, U.: A network suitable microwave radiometer for operational monitoring of the cloudy atmosphere, Atmos. Res., 75, 183-200, doi:10.1016/j.atmosres.2004.12.005, 2005). Values of IWV are derived by zenith measurements of BTs sampled at 2 s resolution, while TP are obtained by BTs sampled in the scanning mode with a temporal resolution of 15 minutes. Both the values of IWV and TP are estimated using a statistical multiple linear regression approach (Löhnert and Crewell, 2003) developed using 2250 high resolution radiosounding from Arctic stations (Thule, Eureka, Alert, Edgeminsonde, Danmarkshavn), which provides the regression coefficients to derive the IWV and TP from the measured BTs.

Description: Ship traffic, population, infrastructure development, and mining activities are expected to increase in the Arctic due to its rising temperatures. This is expected to produce a major impact on aerosol composition. Metals contained in atmospheric particles are powerful markers and can be extremely helpful to gain insights on the different aerosol sources. Thiswork aims at studying the sources of metals in the Arctic aerosol sampled at the Thule High Arctic Atmospheric Observatory (THAAO; Greenland, 76.5°N 68.8°W). Due to the particular composition of Greenlandic soils and to properties of other sources, it was possible to find several signatures of natural and anthropogenic aerosols transported from local and long-range regions. Arctic haze (AH) at Thule builds up on long-range transported aerosol mainly from Canada and Nord America. From a chemical standpoint, this aerosol is characterized by a high concentration of sulfate, Pb, As and Cd and by a La/Ce ratio larger than 1. The Ti/Al and Fe/Al ratios in the AH aerosol are lower (Ti/Al = 0.04 w/w; Fe/ Al= 0.79 w/w) than for local aerosol (Ti/Al= 0.07 w/w; Fe/Al = 0.89 w/w). Conversely, aerosol arising from coastal areas of South-West Greenland is characterized by a high concentration of V,Ni, and Cr. These metals, generally considered anthropogenic, arise heremainly fromnatural crustal sources. In some summer samples, however, the V/Ni ratio becomes larger than 3. In particular, cases displaying this characteristic ratio, as also shown by backward trajectories, are associated with sporadic transport to Thule of ship aerosol from ships passing through Baffin Bay and arriving to Thule during summer. Although further measurements are necessary to confirm the discussed results, the analysis carried out in this work on a large number of metals sampled in coastal Greenland aerosol is unprecedented.

Description: Published

Description: 140511

Description: 5A. Ricerche polari e paleoclima

Description: JCR Journal

Description: The Arctic climate is influenced by the interaction of shortwave (SW) and longwave (LW) radiation with the atmosphere and the surface. The comprehensive evolution of the Surface Radiative Fluxes (SRF) on different time scales is of paramount importance to understanding the complex mechanisms governing the Arctic climate. However, only a few sites located in the Arctic region provide long-term time series of SRF allowing for capturing the seasonality of atmospheric and surface parameters and carrying out validation of satellite products and/or reanalyses. This paper presents the daily and monthly SRF record collected at the Thule High Arctic Atmospheric Observatory (THAAO, 76.5° N, 68.8° W), in North-Western Greenland. The downwelling components of the SW (DSI) and the LW (DLI) irradiances have been measured at THAAO since 2009, while the collection of the upwelling SW (USI) and LW (ULI) irradiance was started in 2016, together with additional measurements, such as e.g., meteorological parameters and column water vapour. The datasets of DSI (Meloni et al., 2022a; https://doi.org/10.13127/thaao/dsi), USI (Meloni et al., 2022b; https://doi.org/10.13127/thaao/usi), DLI (Meloni et al., 2022c; https://doi.org/10.13127/thaao/dli), ULI (Meloni et al., 2022d; https://doi.org/10.13127/thaao/uli), and near surface air temperature (Muscari et al., 2018; https://doi.org/10.13127/thaao/met), can be accessed through the THAAO web site (https://www.thuleatmos-it.it/data). DSI is absent (solar zenith angle≥90°) from 29 October to 13 February, assuming maxima in June (monthly mean of 277.0 Wm-2), when it is about half of the total incoming irradiance. The USI maximum occurs in May (132.4 Wm-2) due to the combination of moderately high DSI values and high albedo. The shortwave surface albedo (A) assumes an average of 0.16 during summer, when the surface is free of snow. Differently, during months of snow-covered surface, when solar radiation allows estimating A, its values are greater than 0.6. A large interannual variability is observed in May and September, months characterized by rapidly changing surface conditions, which appear to be linked with air temperature anomalies. DLI and ULI maxima occur in July and August, and minima in February and March. ULI is always larger than DLI and shows a wider annual cycle. ULI is well described by a fourth-order polynomial fit to the air temperature (R2〉0.99 for monthly data and R2〉0.97 for daily data). The surface radiation budget (SRB) is positive from April to August, when absorption of solar radiation exceeds the infrared net cooling, with a maximum value of 153.2 Wm-2 in June. From November to February, during the polar night, the LW net flux varies between -34.5 and -43.0 Wm-2. In March and September, the negative LW net flux overcomes the positive SW contribution, producing a negative SRB. THAAO measurements show clear evidence of the influence of several regional weather/climate events, which appear strongly linked with SRF anomalies. These anomalies are found for example during summer 2012, when a large ice melting event took place over Greenland, and during winter 2019–2020, extraordinarily cold in the Arctic region.

Description: In press

Description: OSA2: Evoluzione climatica: effetti e loro mitigazione

Description: JCR Journal

Description: Ground-based high resolution observations of downward longwave irradiance (DLI), surface air temperature, water vapour surface partial pressure and column amount, zenith sky infrared (IR) radiance in the atmospheric window, and all-sky camera images are regularly obtained at the Thule High Arctic Atmospheric Observatory (THAAO, 76.5° N, 68.8° W), North-West Greenland. The datasets for the years 2017 and 2018 have been used to assess the performance of different empirical formulas to infer clear sky DLI. An algorithm to identify clear sky observations has been developed, based on value, variability, and persistence of zenith sky IR radiance. Seventeen different formulas to estimate DLI have been tested against the THAAO dataset, using the originally determined coefficients. The formulas which combine information on total column water vapour and surface air temperature appear to perform better than others, with a mean bias with respect to the measured DLI smaller than 1 W/m2 and a root mean squared error (RMSE) around 6 W/m2. Some formulas, specifically developed for the Arctic, are found to produce poor statistical results; this is attributed partly to limitations in the originally used dataset, which does not cover a whole year, or is relative to very specific conditions (i.e., the ice sheet). The bias displays a significant improvement when the coefficients of the different formulas are calculated using the THAAO dataset. The presence of two full years of data allows the investigation of the inter-annual variability, and the use of different years for the determination of the coefficients and the evaluation of results. The smallest values of the bias and RMSE reach 0.1 W/m2 and 5 W/m2, respectively. Overall, best results are found for formulas which use both surface parameters and total water vapour column, and have been developed from global datasets. Conversely, formulas which express the atmospheric emissivity as a linear function of the logarithm of the column integrated water vapour appear to poorly reproduce the observations at THAAO.

Description: In press

Description: OSA2: Evoluzione climatica: effetti e loro mitigazione

Description: JCR Journal

Description: 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 500MHz 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 180K 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 1 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.

Description: Italian Antarctic Programme (PNRA) funded by MIUR through projects 2013/C3.03 and 2015/B3.01. Progetto Premiale ARCA.

Description: Published

Description: 1099-2018

Description: 5A. Paleoclima e ricerche polari

Description: JCR Journal

Description: In remote marine areas, biogenic productivity and atmospheric particulate are coupled through dimethylsulfide (DMS) emission by phytoplankton. Once in the atmosphere, the gaseous DMS is oxidized to produce H2SO4 and methanesulfonic acid (MSA); both species can a ect the formation of cloud condensation nuclei. This study analyses eight years of biogenic aerosol evolution and variability at two Arctic sites: Thule (76.5 N, 68.8 W) and Ny Ålesund (78.9 N, 11.9 E). Sea ice plays a key role in determining the MSA concentration in polar regions. At the beginning of the melting season, in April, up to June, the biogenic aerosol concentration appears inversely correlated with sea ice extent and area, and positively correlated with the extent of the ice-free area in the marginal ice zone (IF-MIZ). The upper ocean stratification induced by sea ice melting might have a role in these correlations, since the springtime formation of this surface layer regulates the accumulation of phytoplankton and nutrients, allowing the DMS to escape from the sea to the atmosphere. The multiyear analysis reveals a progressive decrease in MSA concentration in May at Thule and an increase in July August at Ny Ålesund. Therefore, while the MSA seasonal evolution is mainly related with the sea ice retreat in April, May, and June, the IF-MIZ extent appears as the main factor a ecting the longer-term behavior of MSA.

Description: MIUR PRIN 2007 and PRIN 2009, PNRA 2010-2012, PNRA 2015-2016, PNRA 2016-2018

Description: Published

Description: id 349

Description: 5A. Ricerche polari e paleoclima

Description: JCR Journal