Search results for "Diurnal cycle"
showing 10 items of 24 documents
Insights into the summer diurnal cycle over Eastern South Africa.
2018
Abstract Adopting a state-of-the-art numerical model system, we investigate how the diurnal variations in precipitation and local breeze systems are characterized by lower-boundary conditions related to the Drakensberg highland and warm SST associated with the Agulhas Current. A control simulation can simulate the hydrometeorological climates in the region realistically, but the terrestrial rainfall is overestimated. During daytime, the precipitation is confined to the Drakensberg highland, and there is an onshore local breeze, while during midnight to morning, the rainfall is confined to the Agulhas Current, and the breeze is offshore. These variations are captured by the numerical simulat…
Development of a general model to estimate the instantaneous, daily, and daytime net radiation with satellite data on clear-sky days
2015
Net radiation is a key variable in computing evapotranspiration and is a driving force in many other physical and biological processes. Remote sensing techniques provide an unparalleled spatial and temporal coverage of land-surface attributes, and thus several studies have attempted to estimate net radiation by combining remote sensing observations with surface and atmospheric data. However, remote sensing provides instantaneous data, when many applications and models need information at other temporal scales. In this work, a new general methodology is proposed to estimate daily and daytime net radiation and to retrieve the diurnal cycle of net radiation. Four images were acquired on differ…
The 1-way on-line coupled model system MECO(n) – Part 4: Chemical evaluation (based on MESSy v2.52)
2016
Abstract. For the first time a simulation incorporating tropospheric and stratospheric chemistry using the newly developed MECO(n) model system is performed. MECO(n) is short for MESSyfied ECHAM and COSMO model nested n-times. It features an on-line coupling of the COSMO-CLM model, equipped with the Modular Earth Submodel System (MESSy) interface (called COSMO/MESSy), with the global atmospheric chemistry model ECHAM5/MESSy for Atmospheric Chemistry (EMAC). This on-line coupling allows a consistent model chain with respect to chemical and meteorological boundary conditions from the global scale down to the regional kilometre scale. A MECO(2) simulation incorporating one regional instance ov…
Remote sensing of chlorophyll fluorescence for estimation of stress in vegetation. Recommendations for future missions
2007
Vegetation monitoring is a key issue in Earth Observation due to its relation with the global CO2 cycle. Chlorophyll fluorescence (ChF) emitted by the vegetation is an accurate indicator of the plant status and their photosynthetic activity. This work analyses the diurnal evolution of the ChF emission spectrum and the fluorescence yield in order to determine the best conditions for remote sensing of ChF from a satellite platform. The ChF evolution is studied at leaf level during several diurnal cycles, in simulated conditions, for two species under different stress conditions. The analysis of the signal levels gives an estimation of the values of ChF emission which could be observed from a …
Sensitivity of low-level clouds and precipitation to anthropogenic aerosol emission in southern West Africa: a DACCIWA case study
2021
Abstract. During the West African summer monsoon, pollutants emitted in urbanized coastal areas modify cloud cover and precipitation patterns. The Dynamics-Aerosol-Chemistry-Cloud-Interactions in West Africa (DACCIWA) field campaign provided numerous aircraft-based and ground-based observations, which are used here to evaluate two experiments made with the coupled WRF-CHIMERE model, integrating both the direct and indirect aerosol effect on meteorology. During one well-documented week (1–7 July 2016), the impacts of anthropogenic aerosols on the diurnal cycle of low-level clouds and precipitation are analyzed in detail using high and moderate intensity of anthropogenic emissions in the expe…
Superparameterised cloud effects in the EMAC general circulation model (v2.50) – influences of model configuration
2020
A new module has been implemented in the fifth generation of the ECMWF/Hamburg (ECHAM5)/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model that simulates cloud-related processes on a much smaller grid. This so-called superparameterisation acts as a replacement for the convection parameterisation and large-scale cloud scheme. The concept of embedding a cloud-resolving model (CRM) inside of each grid box of a general circulation model leads to an explicit representation of cloud dynamics. The new model component is evaluated against observations and the conventional usage of EMAC using a convection parameterisation. In particular, effects of applying different configurat…
Study of the diurnal cycle of stressed vegetation for the improvement of fluorescence remote sensing
2006
Chlorophyll fluorescence (Chf) emission allows estimating the photosynthetic activity of vegetation - a key parameter for the carbon cycle models - in a quite direct way. However, measuring Chf is difficult because it represents a small fraction of the radiance to be measured by the sensor. This paper analyzes the relationship between the solar induced Chf emission and the photosynthetically active radiation (PAR) in plants under water stress condition. The solar induced fluorescence emission is measured at leaf level by means of three different methodologies. Firstly, an active modulated light fluorometer gives the relative fluorescence yield. Secondly, a quantitative measurement of the Ch…
Sensitivity analysis of the fraunhofer line discrimination method for the measurement of chlorophyll fluorescence using a field spectroradiometer
2007
The Fraunhofer Line Discrimination (FLD) principle is established as a good method for remote sensing of solar induced chlorophyll fluorescence. Some improvements to the method are analysed in order to determine and reduce the sources of error in the estimation of the fluorescence emission. A sensitivity analysis has been performed over simulated data generated from real diurnal cycle measurements.
Effects of model configuration for superparametrised long-term simulations – Implementation of a cloud resolving model in EMAC (v2.50)
2019
Abstract. A new module has been implemented in the ECHAM5/MESSy Atmospheric Chemistry (EMAC) Model that simulates cloud related processes on a much smaller grid. This so called superparametrisation acts as a replacement for the convection parametrisation and large-scale cloud scheme. The concept of embedding an ensemble of cloud resolving models (CRMs) inside of each grid box of a general circulation model leads to an explicit representation of cloud dynamics. The new model component is evaluated against observations and the conventional usage of EMAC using a convection parametrisation. In particular, effects of applying different configurations of the superparametrisation are analyzed in a…
Evaluation of remote sensing of vegetation fluorescence by the analysis of diurnal cycles
2008
Chlorophyll fluorescence (ChF) emission is a direct indicator of the photosynthetic activity of vegetation, which is a key parameter of the carbon cycle. This paper analyses chlorophyll fluorescence evolution at leaf level during a complete diurnal cycle in simulated and natural conditions, for two species under different stress conditions. Absolute spectral radiance of the ChF emission is obtained allowing a quantitative derivation of the fluorescence yield of the ChF, which correlates well with established fluorescence instruments. The studied cases show that the ChF emission is mainly driven by the photosynthetic active radiation during the whole cycle, but the fluorescence yield is seve…