Anna Maria Sempreviva

Mixing Height Over Water And Its Role On The Correlation Between Temperature And Humidity Fluctuations In The Unstable Surface Layer

Results from an experimental investigation of themixing height over inner Danish waters carriedout from September 1990 to October 1992, are discussed.The statistical analysis of the mixed-layer height (zi)over the sea does not exhibit the dailyvariation that is characteristic of the mixed layerover land, but it is nearly constant over a24-hour cycle. During summer, the mixed layer ishigher than during winter. A second inversionwas often observed.A case study of the development of the mixed layerover the sea under near-neutral and unstableatmospheric conditions during six consecutivedays is presented. A zero-order mixed-layer heightmodel is applied. In addition to momentum and heatfluxes the effect of subsidence was found to be importantfor the evolution of the mixed layer over the sea. Themodelled evolution of zi compared successfullywith measurements.We have investigated the influence of themixed-layer height on the correlation coefficient RqTbetween temperature and humidity fluctuations usingthe values obtained with the model.We found that the evolution of RqT follows theevolution of the mixing height. An empirical modellinking the surface values of RqT to zi and the Obukhov scaling length L has been suggested. The modelreproduces the experimental features.

Transport of temperature and humidity variance and covariance in the marine surface layer

In this paper we address the budget of potential temperature T and moisture mixing ratio q variances as well as the q-T covariance budget. We focus on the vertical transport and study the quantities contained in these terms. Estimates of transport terms are rare and to the best of our knowledge they have never been shown together in the literature. For this purpose an extensive set of humidity and temperature turbulence data from two heights in a marine environment has been analysed. We discuss and compare our results with results from earlier studies for a range of stability from near-neutral to unstable. Similarity and differences between T and q behaviour in the surface layer over water are presented.

Humidity fluctuations in the marine boundary layer measured at a coastal site with an infrared humidity sensor

An extensive set of humidity turbulence data has been analyzed from 22-m height in the marine boundary layer. Fluctuations of humidity were measured by an “OPHIR”, an infrared humidity sensor with a 10 Hz scanning frequency and humidity spectra were produced. The shapes of the normalized spectra follow the established similarity functions. However the 10-min time averaged measurements underestimate the value of the absolute humidity. The importance of the humidity flux contribution in a marine environment in calculating the Obukhov stability length has been studied. Deviations from Monin-Obukhov similarity theory seem to be connected to a low correlation between humidity and temperature.

On the Temperature and Humidity Dissimilarity in the Marine Surface Layer

The dissimilarity of temperature and humidity transfer in the marine surface layer (MSL) is investigated through the relative transport efficiency and correlation coefficient of these two scalars. We examine their variability and relationship with mean values, as well as spectral characteristics. It is shown that the dissimilarity between these two scalars in the MSL is a function of stability, the boundary-layer depth, and flow steadiness. In general the temperature and humidity are less correlated in shallow marine boundary layers compared to deep marine boundary layers, due to the stronger impact of the boundary-layer scale in breaking the “same source, same sink” assumption for scalar similarity. This is supported by the combination of our spectral analysis of scalar fluxes and corresponding measured and modelled boundary-layer depth. This assumption is also broken in near-neutral conditions, when there is an efficient latent heat transfer but negligible sensible heat transfer. Our data suggest that parametrization of humidity fluxes via similarity theory could still be reliable when the correlation coefficient

Deposition of Nitrogen Compounds to the Danish Coastal Waters

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On the Anomalous Behaviour of Scalar Flux–Variance Similarity Functions Within the Canopy Sub-layer of a Dense Alpine Forest

>0.5, and in near-neutral conditions the humidity flux can be estimated without use of the sensible heat flux.

Offshore wind climatology over the Mediterranean basin

Neste trabalho investiga-se a camada limite atmosferica marinha diurna empregando a simulacao dos grandes turbilhoes (LES) e observacoes atmosfericas do Ligurian Air-Sea Interaction Experiment (LASIE). O codigo LES utilizado neste trabalho foi modificado para descrever a evolucao da camada limite sobe o mar. Os resultados da analise mostram que o modelo LES realistico e adequado para simular a camada limite atmosferica marinha.

The Temperature-Humidity Covariance in the Marine Surface Layer : A One-dimensional Analytical Model

Methods, parameterisations and models have been developed, which give insight in processes that are important for deposition of nitrogen compounds to the sea. This knowledge has been applied to the Kattegat Strait for which a nitrogen deposition of 960 kg N km-2 yr-1 was calculated with an atmospheric transport model.