The Total Solar Eclipse of March 2006: overview

International audienceThis paper provides an overview of integrated, multi-disciplinary effort to study the effects of a total solar eclipse on the environment, with special focus on the atmosphere. On the occasion of the 29 March 2006 total solar eclipse, visible over the Eastern Mediterranean, several research and academic institutes organised co-ordinated experimental campaigns, at different distances from the totality and in various environments in terms of air quality. The detailed results are presented in a number of scientific papers included in a Special Issue of Atmospheric Chemistry and Physics. The effects of the eclipse on the meteorology and the spectral solar radiation, the chemical response of the atmosphere to the abrupt "switch off" of the sun and the induced changes in the stratosphere and the ionosphere, have been among the issues covered. The rare event of a total solar eclipse provided the opportunity to evaluate 1-D and 3-D radiative transfer models (in the atmosphere and underwater), mesoscale meteorological, regional air quality and photochemical box models, against measurements. Within the challenging topics of this effort has been the investigation of eclipse impacts on ecosystems (field crops and marine plankton) and the identification of eclipse induced gravity waves, for the first time with simultaneous measurements at three altitudes namely the troposphere, the stratosphere and the ionosphere

Urban energy exchanges monitoring from space

One important challenge facing the urbanization and global environmental change community is to understand the relation between urban form, energy use and carbon emissions. Missing from the current literature are scientific assessments that evaluate the impacts of different urban spatial units on energy fluxes; yet, this type of analysis is needed by urban planners, who recognize that local scale zoning affects energy consumption and local climate. However, satellite-based estimation of urban energy fluxes at neighbourhood scale is still a challenge. Here we show the potential of the current satellite missions to retrieve urban energy budget, supported by meteorological observations and evaluated by direct flux measurements. We found an agreement within 5% between satellite and in-situ derived net all-wave radiation; and identified that wall facet fraction and urban materials type are the most important parameters for estimating heat storage of the urban canopy. The satellite approaches were found to underestimate measured turbulent heat fluxes, with sensible heat flux being most sensitive to surface temperature variation (-64.1, +69.3 W m-2 for ±2 K perturbation); and also underestimate anthropogenic heat flux. However, reasonable spatial patterns are obtained for the latter allowing hot-spots to be identified, therefore supporting both urban planning and urban climate modelling

The use of scenarios and models to evaluate the future of nature values and ecosystem services in Mediterranean forests

Science and society are increasingly interested in predicting the effects of global change and socio-economic development on natural systems, to ensure maintenance of both ecosystems and human well-being. The Intergovernmental Platform on Biodiversity and Ecosystem Services has identified the combination of ecological modelling and scenario forecasting as key to improving our understanding of those effects, by evaluating the relationships and feedbacks between direct and indirect drivers of change, biodiversity, and ecosystem services. Using as case study the forests of the Mediterranean basin (complex socio-ecological systems of high social and conservation value), we reviewed the literature to assess (1) what are the modelling approaches most commonly used to predict the condition and trends of biodiversity and ecosystem services under future scenarios of global change, (2) what are the drivers of change considered in future scenarios and at what scales, and (3) what are the nature and ecosystem service indicators most commonly evaluated. Our review shows that forecasting studies make relatively little use of modelling approaches accounting for actual ecological processes and feedbacks between different socio-ecological sectors; predictions are generally made on the basis of a single (mainly climate) or a few drivers of change. In general, there is a bias in the set of nature and ecosystem service indicators assessed. In particular, cultural services and human well-being are greatly underrepresented in the literature. We argue that these shortfalls hamper our capacity to make the best use of predictive tools to inform decision-making in the context of global change.This work was supported by the Spanish Government through the INMODES project (grant number CGL2017-89999-C2-2-R), the ERA-NET FORESTERRA project INFORMED (grant number 29183), and the project Boscos Sans per a una Societat Saludable funded by Obra Social la Caixa (https://obrasociallacaixa.org/). AMO and AA were supported by Spanish Government through the “Juan de la Cierva” fellowship program (IJCI-2016-30349 and IJCI-2016-30049, respectively). JVRD was supported by the Government of Asturias and the FP7-Marie Curie-COFUND program of the European Commission (Grant “Clarín” ACA17-02)

Wind profile diagnosis from surface routine meteorological data over a coastal area

A simple algorithm is proposed in order to transform routine surface wind speed observations near the coast to a wind at the height of the equilibrium planetary boundary layer as well as to any height over a relatively flat coastal region. The model is based on the well known internal boundary (IBL) concept, Monin-Obukhov similarity theory and the resistance law, and describes the effects of the roughness transition from sea to land as well as the effect of stability on the shape of the profiles and the IBL growth. The required input weather data are not more than surface wind speed, air temperature and total cloud cover. Satisfactory agreement was found between measurements at Hellinikon airport and estimations made with the scheme. The introduction of a transition layer above the IBL did not improve the agreement to any significant extent. Mean values of the estimated wind differed by less than 1 m s-1 from the observed ones, a difference within the accuracy of the reported rawinsonde values. The rms error varied in the range of 17-22% of the observed average value, giving the best agreement under unstable conditions. The correlation coefficient between the observed and the estimated values of the wind, at the height of the equilibrium planetary boundary layer, ranged between 0.74 and 0.90

Synergies between Urban Heat Island and Heat Waves in Athens (Greece), during an extremely hot summer (2012)

Heat waves (HWs) are recognized as a serious threat for human health worldwide, with urban areas being more vulnerable due to the urban heat island (UHI) effect and population density. Yet, in the climate change context, HWs are becoming more frequent, stronger and longer, which, coupled with intensifying urbanization exacerbates thermal risk for urban residents. Despite the profound impact of this global phenomenon there is no clear consensus so far on possible synergies between UHIs and HWs. The study sheds light on the complex synergies between UHIs and HWs focusing on coastal sites. A quite challenging period comprising five HW episodes during summer 2012 in Athens (Greece) was selected for analysis. A positive feedback between UHIs and HWs was found, with intensification of the average UHI magnitude by up to 3.5 °C during HWs, compared to summer background conditions. Our results contribute significantly to understanding synergies between UHIs and HWs that may strongly increase thermal risk in cities and vulnerability of urban population. © 2017 The Author(s)

Nocturnal boundary layer height prediction from surface routine meteorological data

A number of well known diagnostic equations for the determination of the height, h, of the nocturnal boundary layer, with minimum data requirements of at most surface wind speed, air temperature and total cloud cover, have been tested as to their effectiveness. The computed values have been compared with direct estimation of h, from temperature or wind profiles of rawinsonde ascents available at 00Z (02h LST). The comparison between computed and observed values shows that best agreement is found when the nocturnal boundary layer height is determined through wind profiles. The ratio of the computed to the observed values reveals a strong dependence on stability, resulting in overestimation by the models for very low stability and underestimation for strong stability. The simple expressions involving the wind speed rather than other stability parameters resulted in a better overall fit to the observed values. A simple prognostic model is shown to provide the best estimates of the NBL height compared to both wind and temperature profile definition

The effect of the total solar eclipse of 29 March 2006 on meteorological variables in Greece

International audienceThis paper examines the effect of the total solar eclipse of 29 March 2006 on meteorological variables across Greece. Integrated micrometeorological measurements were conducted at Kastelorizo, a small island within the path of totality, and other sites within the Greek domain, with various degrees of solar obscuration. The observations showed a dramatic reduction in the incoming global radiation and subsequent, pronounced changes in surface air temperature with the lowest temperature values occurring about 15 min after the full phase. The amplitude of the air temperature drop was not analogous to the obscuration percentage but was principally determined by the surrounding environment (mainly the sea influence), the background meteorological conditions and local cloudiness. Surface wind-speed decreased in most sites as a result of the cooling and stabilization of the atmospheric boundary layer. This perturbation provided a unique opportunity to apply a sensitivity analysis on the effect of the eclipse to the Weather Research and Forecast (WRF) numerical mesoscale meteorological model. Strong anomalies, not associated with a dynamic response, were simulated over land especially in surface air temperature. The simulated temperature drop pattern was consistent with the observations