Soren E. Larsen

The influence of thermal effects on the wind speed profile of the coastal marine boundary layer

The wind speed profile in a coastal marine environment is investigated with observations from the measurement program Rødsand, where meteorological data are collected with a 50 m high mast in the Danish Baltic Sea, about 11 km from the coast. When compared with the standard Monin—Obukhov theory the measured wind speed increase between 10 m and 50 m height is found to be systematically larger than predicted for stable and near-neutral conditions. The data indicate that the deviation is smaller for short (10–20 km) distances to the coast than for larger (>30 km) distances.The theory of the planetary boundary layer with an inversion lid offers a qualitative explanation for these findings. When warm air is advected over colder water, a capping inversion typically develops. The air below is constantly cooled by the water and gradually develops into a well-mixed layer with near-neutral stratification. Typical examples as well as scatter plots of the data are consistent with this explanation. The deviation of measured and predicted wind speed profiles is shown to be correlated with the estimated height and strength of the inversion layer.

Response of neutral boundary layers to changes of roughness

When air blows across a change in surface roughness, an internal boundary layer (IBL) develops within which the wind adapts to the new surface. This process is well described for short fetches, > 1 km. However, few data exist for large fetches on how the IBL grows to become a new equilibrium boundary layer where again the drag laws can be used to estimate the surface wind.To study this problem, data have been sampled for two years from four 30-m meteorological masts placed from 0 to 30 km inland from the North Sea coast of Jutland in Denmark. The present analysis is limited to neutral stratification, and the surface roughness is the main parameter. The analysis of wind data and two simple models, a surface layer and a planetary boundary layer (PBL) model, are described.Results from both models are discussed and compared with data analysis. Model parameters have been evaluated and the model sensitivity to those parameters has been investigated. Using the model parameters, a large-scale roughness length has been estimated.

Meteorological aspects of offshore wind energy: Observations from the Vindeby wind farm

The Vindeby monitoring project has been established to provide information on the worlds first offshore wind farm at Vindeby, Denmark. Over the course of the project, different aspects of offshore meteorology which are relevant to offshore wind energy production will be examined in addition to turbine loading and behaviour in offshore conditions. Here, the simplest aspects of coastal meteorology are investigated, namely, wind speed differences between land and sea, wind speed profiles, diurnal variability and turbine wake effects. Observations are compared with simple prediction methods in order to test commonly held assumptions about the differences between the wind climate over land and sea and also with results from Risos WAsP model.

Network science landers for Mars

Abstract The NetLander Mission will deploy four landers to the Martian surface. Each lander includes a network science payload with instrumentation for studying the interior of Mars, the atmosphere and the subsurface, as well as the ionospheric structure and geodesy. The NetLander Mission is the first planetary mission focusing on investigations of the interior of the planet and the large-scale circulation of the atmosphere. A broad consortium of national space agencies and research laboratories will implement the mission. It is managed by CNES (the French Space Agency), with other major players being FMI (the Finnish Meteorological Institute), DLR (the German Space Agency), and other research institutes. According to current plans, the NetLander Mission will be launched in 2005 by means of an Ariane V launch, together with the Mars Sample Return mission. The landers will be separated from the spacecraft and targeted to their locations on the Martian surface several days prior to the spacecrafts arrival at Mars. The landing system employs parachutes and airbags. During the baseline mission of one Martian year, the network payloads will conduct simultaneous seismological, atmospheric, magnetic, ionospheric, geodetic measurements and ground penetrating radar mapping supported by panoramic images. The payloads also include entry phase measurements of the atmospheric vertical structure. The scientific data could be combined with simultaneous observations of the atmosphere and surface of Mars by the Mars Express Orbiter that is expected to be functional during the NetLander Missions operational phase. Communication between the landers and the Earth would take place via a data relay onboard the Mars Express Orbiter.

Aspects Of The Atmospheric Surface Layers On Mars And Earth

The structures of mean flow and turbulence in the atmospheric surface boundary layer have been extensively studied on Earth, and to a far less extent on Mars, where only the Viking missions and the Pathfinder mission have delivered in-situ data. Largely the behaviour of surface-layer turbulence and mean flow on Mars is found to obey the same scaling laws as on Earth. The largest micrometeorological differences between the two atmospheres are associated with the low air density of the Martian atmosphere. Together with the virtual absence of water vapour, it reduces the importance of the atmospheric heat flux in the surface energy budget. This increases the temperature variation of the surface forcing the near-surface temperature gradient and thereby the diabatic heat flux to higher values than are typical on the Earth, resulting in turn in a deeper daytime boundary layer. As wind speed is much like that of the Earth, this larger diabatic heat flux is carried mostly by larger maximal values of T*, the surface scale temperature. The higher kinematic viscosity yields a Kolmogorov scale of the order of ten times larger than on Earth, influencing the transition between rough and smooth flow for the same surface features.The scaling laws have been validated analysing the Martian surface-layer data for the relations between the power spectra of wind and temperature turbulence and the corresponding mean values of wind speed and temperature. Usual spectral formulations were used based on the scaling laws ruling the Earth atmospheric surface layer, whereby the Earths atmosphere is used as a standard for the Martian atmosphere.

The NetLander atmospheric instrument system (ATMIS): description and performance assessment

Abstract The pointwise meteorological observations of the Viking Lander and Mars Pathfinder as well as the orbital mapping and sounding performed by, e.g., Mariner 9, Viking Orbiters and the Mars Global Surveyor have given a good understanding of the basic behaviour of the Martian atmosphere. However, the more detailed characterisation of the Martian circulation patterns, boundary layer phenomena and climatological cycles requires deployment of meteorological surface networks. The European NetLander concept comprising four well-instrumented landers is being studied for launch in 2005 and operations spanning at least a Martian year in 2006–2008. The landers are to be deployed to areas in both Martian hemispheres from equatorial regions to low mid-latitudes. The NetLander atmospheric instrument system (ATMIS) on board each of the landers is designed to measure atmospheric vertical profiles of density, pressure and temperature during the descent onto the surface, as well as pressure, atmospheric and ground temperatures, wind, atmospheric optical thickness and humidity through a full Martian year, possibly beyond. The main operational objective of this meteorological experiment is to provide a regular time series of the meteorological parameters as well as accelerated measurement campaigns. Such a data set would substantially improve our understanding of the atmospheric structure, dynamics, climatological cycles, and the atmosphere–surface interactions. The ATMIS sensor systems and measurement approaches described here are based on solutions and technologies tested for similar observations on Mars-96, Mars Pathfinder, Huygens, and Mars Polar Lander. Although the number of observation sites only permits characterisation of some components of the general circulation, the NetLander ATMIS will more than double the number of in situ vertical profiles (only three profiles — two from Viking Landers and one from Mars Pathfinder — are currently available and as envisioned at the time of writing, none of the 2001 and 2003 landers’ payloads include entry phase measurements of pressure or temperature), perform the first in situ meteorological observations in the southern low- and mid-latitudes and provide the first simultaneous in situ multi-site observations of the local and general circulation patterns, in a variety of locations and terrains. As such, NetLander ATMIS will be the precursor of more comprehensive meteorological surface networks for future Mars exploration.