The Høvsøre Tall Wind-Profile Experiment: A Description of Wind Profile Observations in the Atmospheric Boundary Layer

We present an analysis of data from a nearly 1-year measurement campaign performed at Høvsøre, Denmark, a coastal farmland area where the terrain is flat. Within the easterly sector upstream of the site, the terrain is nearly homogenous. This topography and conditions provide a good basis for the analysis of vertical wind-speed profiles under a wide range of atmospheric stability, turbulence, and forcing conditions. One of the objectives of the campaign was to serve as a benchmark for flow over flat terrain models. The observations consist of combined wind lidar and sonic anemometer measurements at a meteorological mast. The sonic measurements cover the first 100 m and the wind lidar measures above 100 m every 50 m in the vertical. Results of the analysis of observations of the horizontal wind-speed components in the range 10–1200 m and surface turbulence fluxes are illustrated in detail, combined with forcing conditions derived from mesoscale model simulations. Ten different cases are presented. The observed wind profiles approach well the simulated gradient and geostrophic winds close to the simulated boundary-layer height during both barotropic and baroclinic conditions, respectively, except for a low-level jet case, as expected. The simulated winds are also presented for completeness and show good agreement with the measurements, generally underpredicting the turning of the wind in both barotropic and baroclinic cases.     

Variations of atmospheric 14C concentrations over the Alleroød-Younger Dryas transition

Highly variable atmospheric radiocarbon concentrations are a distinct feature during the last deglaciation. The synchronisation of two high-resolution AMS ¹⁴C-dated records, Lake Go?ci??, and a floating Late Weichselian glacial varve chronology at the Allerød-Younger Dryas transition allowed us to assess in detail atmospheric Δ¹⁴C changes between late Allerød and early Preboreal. The combined data set shows a drastic rise in Δ¹⁴C during the first 200 years or so of Younger Dryas and the two following about 500 year-long ¹⁴C plateaux. Model experiments which included variations in the geomagnetic field, atmospheric CO₂ variations and a drastic reduction in North Atlantic Deep Water flux at the onset of Younger Dryas allowed to reproduce the distinct rise in Δ¹⁴C during the first 200 years of Younger Dryas fairly well. Also the drop in Δ¹⁴C at the Younger Dryas/Holocene boundary seems reasonably explained by changes in North Atlantic Deep Water circulation. However, the reason behind the anomalous behaviour of the Δ¹⁴C signal in the middle of Younger Dryas remains an open question.     

Indication of shrinking atmosphere above Tromsø (69°N, 19°E)

At Tromsø (69°N; 19°E), ionospheric data from 1952 onwards indicate that the mean altitude of the F2 layer is dropping by 4 km per decade on average. This effect is thought to be attributable to middle atmosphere cooling due to increasing concentrations of anthropogenic carbon dioxide and methane.