H.P. Schmid

Montane ecosystem productivity responds more to global circulation patterns than climatic trends

Regional ecosystem productivity is highly sensitive to inter-annual climate variability, both within and outside the primary carbon uptake period. However, Earth system models lack sufficient spatial scales and ecosystem processes to resolve how these processes may change in a warming climate. Here, we show, how for the European Alps, mid-latitude Atlantic ocean winter circulation anomalies drive high-altitude summer forest and grassland productivity, through feedbacks among orographic wind circulation patterns, snowfall, winter and spring temperatures, and vegetation activity. Therefore, to understand future global climate change influence to regional ecosystem productivity, Earth systems models need to focus on improvements towards topographic downscaling of changes in regional atmospheric circulation patterns and to lagged responses in vegetation dynamics to non-growing season climate anomalies.

Measuring the 3-D wind vector with a weight-shift microlight aircraft

This study investigates whether the 3-D wind vector can be measured reliably from a highly transportable and low-cost weight-shift microlight aircraft. Therefore we draw up a transferable procedure to accommodate flow distortion originating from the aircraft body and -wing. This procedure consists of the analysis of aircraft dynamics and seven successive calibration steps. For our aircraft the horizontal wind components receive their greatest single amendment (14 %, relative to the initial uncertainty) from the correction of flow distortion magnitude in the dynamic pressure computation. Conversely the vertical wind component is most of all improved (31 %) by subsequent steps considering the 3-D flow distortion distribution in the flow angle computations. Therein the influences of the aircraft’s trim (53 %), as well as changes in the aircraft lift (16 %) are considered by using the measured lift coefficient as explanatory variable. Three independent lines of analysis are used to evaluate the quality of the wind measurement: (a) A wind tunnel study in combination with the propagation of sensor uncertainties defines the systems input uncertainty to ≈0.6 m s−1 at the extremes of a 95 % confidence interval. (b) During severe vertical flight manoeuvres the deviation range of the vertical wind component does not exceed 0.3 m s −1. (c) The comparison with ground based wind measurements yields an overall operational uncertainty (root mean square error) of ≈0.4 m s−1 for the horizontal and≈0.3 m s−1 for the vertical wind components. No conclusive dependence of the uncertainty on the wind magnitude ( <8 m s−1) or true airspeed (ranging from 23–30 m s −1) is found. Hence our analysis provides the necessary basis to study the wind measurement precision and spectral quality, which is prerequisite for reliable Eddy-Covariance flux measurements. Correspondence to: W. Junkermann (wolfgang.junkermann@kit.edu)

A Simple New Model for Incoming Solar Radiation Dependent Only on Screen-Level Relative Humidity

AbstractGlobal incoming shortwave radiation (Rg) is the energy source for the majority of biogeochemical processes on Earth as well as for photovoltaic power production. Existing simple site-specific models to estimate Rg commonly use the daily range of air temperature as input variables. Here, the authors present a simple model for incoming shortwave radiation, requiring only screen-level relative humidity data (and site-specific astronomical information). The model was developed and parameterized using high-quality global radiation data covering a broad range of climate conditions. It was evaluated at independent sites, which were not involved in the process of model development and parameterization. The mean 1:1 slope was 1.02 with an average r2 of 0.98. Normalized root-mean-square error (NRMSE) averaged at 43%. Despite its simplicity, the new model clearly outperforms conventional approaches, and it comes close to more labor- and data-intensive alternative models.