Subseasonal predictions bridge the gap between medium‐range weather forecasts and seasonal climate predictions. This time horizon is of crucial importance for many planning purposes, including energy ...production and agriculture. The verification of such predictions is normally done for areal averages of upper‐air parameters. Only few studies exist that verify the forecasts for surface parameters with observational stations, although this is crucial for real‐world applications, which often require such predictions at specific surface locations. With this study we provide an extensive station‐based verification of subseasonal forecasts against 1,637 ground based observational time series across Europe. Twenty years of temperature and precipitation reforecasts of the European Centre for Medium‐Range Weather Forecasts Integrated Forecasting System are used to analyze the period of April 1995 to March 2014. A lead time and seasonally dependent bias correction is performed to correct the daily temperature and precipitation forecasts at all stations individually. Two bias correction techniques are compared, a mean debiasing method and a quantile mapping approach. Commonly used skill scores characterizing different aspects of forecast quality are computed for weekly aggregated forecasts with lead times of 5–32 days. Overall, promising skill is found for temperature in all seasons except spring. Temperature forecasts tend to show higher skill in Northern Europe and in particular around the Baltic Sea, and in winter. Bias correction is shown to be essential in enhancing the forecast skill in all four weeks for most of the stations and for both variables with QM generally performing better.
Key Points
We provide a station based verification of downscaled and bias‐corrected subseasonal temperature and precipitation predictions for entire Europe
Promising skill is found for weekly mean temperature up to 19‐24 days lead time, but limited to lead days 5‐11 for precipitation
Seasonal and spatial variations in the skill of the forecasts are discussed in the context of subseasonal to seasonal predictions
Abstract
The Alpine region recently experienced several dry summers with important and adverse impacts on economy, society and ecology. Here, we analyse drought indicators, evapotranspiration and ...meteorological data from point observations, reanalyses and regional climate model data to assess trends and drivers of summer drought in Switzerland in the period 1981–2020. The drought indicators from station observations and ERA5-Land and ERA5 reanalyses show a tendency towards drier summer half-years (climatic water balance: −39 mm decade
−1
, 0–1 m integrated soil water content: −5 to −7 mm decade
−1
) with a drying in most months from March to October. Both, increasing evapotranspiration (potential evapotranspiration: +21 mm decade
−1
or +7% K
−1
warming; actual evapotranspiration: +8 to +15 mm decade
−1
) and a non-significant precipitation decrease of 17 mm decade
−1
are identified as important and roughly equivalent drivers. The reanalyses show considerable differences for soil water and actual evapotranspiration, especially in drought summers. The ERA5 soil is clearly drier than the one in ERA5-Land. ERA5 evapotranspiration is smallest and partly soil moisture-limited in drought years while evapotranspiration in ERA5-Land is highest, still mainly energy-limited and scales well with temperature (+4% K
−1
warming). ERA5-Land seems to better match with
in situ
measurements of soil water and evapotranspiration than ERA5, but considerable differences with
in situ
measurements remain. Variability and trends of the drought drivers temperature and precipitation are also investigated in the EURO-CORDEX regional climate model ensemble. Most simulations considerably underestimate the recent warming and the ensemble shows a large possible range of precipitation changes with a mean change near zero. The summer precipitation-temperature scaling and the correlation between summer temperature and precipitation on the interannual time scale are mostly overestimated. Our results highlight that the analysis of Central European summer drought evolution and its drivers remains challenging especially with regional climate model data, but considerable uncertainties also exist in reanalyses.
We present an automated dynamic chamber system which is optimised for continuous unattended flux measurements of multiple non-reactive and reactive trace gases on grassland ecosystems. Main design ...features of our system are (a) highly transparent chamber walls consisting of chemically inert material, (b) individual purging flow units for each chamber, and (c) a movable lid for automated opening and closing of the chamber. The purging flow rate was chosen high enough to keep the mean residence time of the chamber air below one minute. This guarantees a proven efficient mixing of the chamber volume and a fast equilibration after lid closing. The dynamic chamber system is able to measure emission as well as deposition fluxes of trace gases. For the latter case, the modification of the turbulent transport by the chamber (compared to undisturbed ambient conditions) is quantitatively described by a bulk resistance concept. Beside a detailed description of the design and functioning of the system, results of field applications at two grassland sites are presented. In the first experiment, fluxes of five trace gases (CO2, H2O, NO, NO2, O3) were measured simultaneously on small grassland plots. It showed that the dynamic chamber system is able to detect the characteristic diurnal cycles with a sufficient temporal resolution. The results also demonstrated the importance of considering the chemical source/sink in the chamber due to gas phase reactions for the reactive compounds of the NO-NO2-O3 triad. In a second field experiment, chamber flux measurements of CO2 and methanol were compared to simultaneous independent eddy covariance flux measurements on the field scale. The fluxes obtained with the two methods showed a very good agreement indicating a minimal disturbance of the chambers on the physiological activity of the enclosed vegetation.
A system for fast ammonia (NH3) measurements with chemical ionisation mass spectrometry (CIMS) based on a commercial Proton Transfer Reaction-Mass Spectrometer (PTR-MS) is presented. It uses electron ...transfer reaction as ionisation pathway and features a drift tube of polyetheretherketone (PEEK) and silica-coated steel. Heating the instrumental inlet and the drift tube to 180 °C enabled an effective time resolution of ~1 s and made it possible to apply the instrument for eddy covariance (EC) measurements. EC fluxes of NH3 were measured over two agricultural fields in Oensingen, Switzerland, following fertilisations with cattle slurry. Air was aspirated close to a sonic anemometer at a flow of 100 STP L min−1 and was directed through a 23 m long 1/2" PFA tube heated to 150 °C to an air-conditioned trailer where the gas was sub-sampled from the large bypass stream. This setup minimised damping of fast NH3 concentration changes between the sampling point and the actual measurement. High-frequency attenuation loss of the NH3 fluxes of 20 to 40% was quantified and corrected for using an empirical ogive method. The instrumental NH3 background signal showed a minor interference with H2O which was characterised in the laboratory. The resulting correction of the NH3 flux after slurry spreading was less than 1‰. The flux detection limit of the EC system was about 5 ng m−2 s−1 while the accuracy of individual flux measurements was estimated 16% for the high-flux regime during these experiments. The NH3 emissions after broad spreading of the slurry showed an initial maximum of 150 μg m−2 s−1 with a fast decline in the following hours.
Abstract
To extract information on elemental components and PM characteristics from smoke number (SN) filter paper, we were performed elemental analysis by micro-PIXE. As a result of elemental ...analysis of the SN filter, information on the elemental composition of jet engine exhaust PM was obtained. Regarding the SN filter, jet engine exhaust PM have been collected for each difference in engine thrust of various aircraft engines at aircraft turbine engines test cells around the world. By periodically analyzing the elemental composition of such the SN filter, it is possible to grasp the characteristics of the emission PM of each aircraft engine and the transformation of the elemental composition of the emission PM with the passage of time of the jet engine. This was thought to lead to the evaluation of jet engine.
Despite recent evidence on an important role of volatile amines in the nucleation of particulate matter, very scarce information is available on their atmospheric abundance and source distribution. ...Previous measurements in animal housings had identified livestock husbandry as the main amine source, with trimethylamine (TMA) being the key component. This has led to the assumption that the agricultural sources for amines are similar as for ammonia, emitted throughout the cascade of animal excretion, storage and application in the field. In this study, we present the first micrometeorological flux measurements as well as dynamic enclosure experiments showing that the amine source strength from stored slurry is negligible, implying significant consequences for the global amine emission inventory. In the case of cattle, amine production is attributed to the animal's rumination activity and exhalation is suggested to be an important emission pathway, similar to the greenhouse gas methane. Fodder like hay and silage also emits volatile amines, potentially assigning these alkaloid compounds a key function in enhancing particle formation in remote areas.
Key Points
Assumptions on the main global amine sources are challanged by true measurements
Cattle amine production is attributed to rumination acitivity
Vegetation in senescent state (hay, silage) is an important global amine source
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