Estimation of the refractive index structure parameter from single-level daytime routine weather data
Boer, A. van de; Moene, A.F. ; Graf, A. ; Simmer, C. ; Holtslag, A.A.M. - \ 2014
Applied Optics 53 (2014)26. - ISSN 1559-128X - p. 5944 - 5960.
obukhov similarity functions - water-vapor - optical turbulence - sonic anemometer - surface fluxes - energy-balance - temperature - radiation - land - heat
Atmospheric scintillations cause difficulties for applications where an undistorted propagation of electromagnetic radiation is essential. These scintillations are related to turbulent fluctuations of temperature and humidity that are in turn related to surface heat fluxes. We developed an approach that quantifies these scintillations by estimating Cn2 from surface fluxes that are derived from single-level routine weather data. In contrast to previous methods that are biased to dry and warm air, our method is directly applicable to several land surface types, environmental conditions, wavelengths, and measurement heights (lookup tables for a limited number of site-specific parameters are provided). The approach allows for an efficient evaluation of the performance of, e.g., infrared imaging systems, laser geodetic systems, and ground-to-satellite optical communication systems.We tested our approach for two grass fields in central and southern Europe, and for a wheat field in central Europe. Although there are uncertainties in the flux estimates, the impact on Cn2 is shown to be rather small. The Cn2 daytime estimates agree well with values determined from eddy covariance measurements for the application to the three fields. However, some adjustments were needed for the approach for the grass in southern Europe because of non-negligible boundary-layer processes that occur in addition to surface-layer processes.
Observational Support for the Stability Dependence of the Bulk Richardson Number across the Stable Boundary Layer
Basu, S. ; Holtslag, A.A.M. ; Caporaso, L. ; Riccio, A. ; Steeneveld, G.J. - \ 2014
Boundary-Layer Meteorology 150 (2014)3. - ISSN 0006-8314 - p. 515 - 523.
self-correlation - resistance laws - surface fluxes - least-squares - model - height - regression - formulations - parameter - breakdown
The bulk Richardson number (Ri Bh ; defined over the entire stable boundary layer) is commonly utilized in observational and modelling studies for the estimation of the boundary-layer height. Traditionally, Ri Bh is assumed to be a quasi-universal constant. Recently, based on large-eddy simulation and wind-tunnel data, a stability-dependent relationship has been proposed for Ri Bh . In this study, we analyze extensive observational data from several field campaigns and provide further support for this newly proposed relationship.
On the temporal upscaling of evapotranspiration from instantaneous remote sensing measurements to 8-day mean daily-sums
Ryu, Y. ; Baldocchi, D.D. ; Black, T.A. ; Moors, E.J. - \ 2012
Agricultural and Forest Meteorology 152 (2012). - ISSN 0168-1923 - p. 212 - 222.
carbon-dioxide exchange - net ecosystem productivity - co2 exchange - energy fluxes - water-vapor - heterogeneous landscape - temperate grassland - daily evaporation - surface fluxes - boundary-layer
The regular monitoring of evapotranspiration from satellites has been limited because of discontinuous temporal coverage, resulting in snapshots at a particular point in space and time. We developed a temporal upscaling scheme using satellite-derived instantaneous estimates of evapotranspiration to produce a daily-sum evapotranspiration averaged over an 8-day interval. We tested this scheme against measured evapotranspiration data from 34 eddy covariance flux towers covering seven plant functional types from boreal to tropical climatic zones. We found that the ratio of a half-hourly-sum of potential solar radiation (extraterrestrial solar irradiance on a plane parallel to the Earth’s surface) between 10:00 hh and 14:00 hh to a daily-sum of potential solar radiation provides a robust scaling factor to convert a half-hourly measured evapotranspiration to an estimate of a daily-sum; the estimated and measured daily sum evapotranspiration showed strong linear relation (r2 = 0.92) and small bias (-2.7%). By comparison, assuming a constant evaporative fraction (the ratio of evapotranspiration to available energy) during the daytime, although commonly used for temporal upscaling, caused 13 underestimation of evapotranspiration on an annual scale. The proposed temporal upscaling scheme requires only latitude, longitude and time as input. Thus it will be useful for developing continuous evapotranspiration estimates in space and time, which will improve continuous monitoring of hydrological cycle from local to global scales.
A comparison of different inverse carbon flux estimation approaches for application on a regional domain
Tolk, L.F. ; Dolman, A.J. ; Meesters, A.G.C.A. ; Peters, W. - \ 2011
Atmospheric Chemistry and Physics 11 (2011). - ISSN 1680-7316 - p. 10349 - 10365.
atmospheric transport - dioxide exchange - european forests - modeling system - surface fluxes - boundary-layer - co2 fluxes - assimilation - sensitivity - tower
We have implemented six different inverse carbon flux estimation methods in a regional carbon dioxide (CO2) flux modeling system for the Netherlands. The system consists of the Regional Atmospheric Mesoscale Modeling System (RAMS) coupled to a simple carbon flux scheme which is run in a coupled fashion on relatively high resolution (10 km). Using an Ensemble Kalman filter approach we try to estimate spatiotemporal carbon exchange patterns from atmospheric CO2 mole fractions over the Netherlands for a two week period in spring 2008. The focus of this work is the different strategies that can be employed to turn first-guess fluxes into optimal ones, which is known as a fundamental design choice that can affect the outcome of an inversion significantly. Different state-of-the-art approaches with respect to the estimation of net ecosystem exchange (NEE) are compared quantitatively: (1) where NEE is scaled by one linear multiplication factor per land-use type, (2) where the same is done for photosynthesis (GPP) and respiration (R) separately with varying assumptions for the correlation structure, (3) where we solve for those same multiplication factors but now for each grid box, and (4) where we optimize physical parameters of the underlying biosphere model for each land-use type. The pattern to be retrieved in this pseudo-data experiment is different in nearly all aspects from the first-guess fluxes, including the structure of the underlying flux model, reflecting the difference between the modeled fluxes and the fluxes in the real world. This makes our study a stringent test of the performance of these methods, which are currently widely used in carbon cycle inverse studies. Our results show that all methods struggle to retrieve the spatiotemporal NEE distribution, and none of them succeeds in finding accurate domain averaged NEE with correct spatial and temporal behavior. The main cause is the difference between the structures of the first-guess and true CO2 flux models used. Most methods display overconfidence in their estimate as a result. A commonly used daytime-only sampling scheme in the transport model leads to compensating biases in separate GPP and R scaling factors that are readily visible in the nighttime mixing ratio predictions of these systems. Overall, we recommend that the estimate of NEE scaling factors should not be used in this regional setup, while estimating bias factors for GPP and R for every grid box works relatively well. The biosphere parameter inversion performs good compared to the other inversions at simultaneously producing space and time patterns of fluxes and CO2 mixing ratios, but non-linearity may significantly reduce the information content in the inversion if true parameter values are far from the prior estimate. Our results suggest that a carefully designed biosphere model parameter inversion or a pixel inversion of the respiration and GPP multiplication factors are from the tested inversions the most promising tools to optimize spatiotemporal patterns of NEE.
Statistical properties of random CO2 flux measurement uncertainty inferred from model residuals
Richardson, A.D. ; Mahecha, M.D. ; Falge, E. ; Kattge, J. ; Moffat, A.M. ; Papale, D. ; Reichstein, M. ; Stauch, V.J. ; Braswell, B.H. ; Churkina, G. ; Kruijt, B. ; Hollinger, D.Y. - \ 2008
Agricultural and Forest Meteorology 148 (2008)1. - ISSN 0168-1923 - p. 38 - 50.
net ecosystem exchange - eddy-covariance measurements - carbon-dioxide exchange - long-term measurements - time-series data - spatial variability - spectral-analysis - soil respiration - turbulent fluxes - surface fluxes
Information about the uncertainties associated with eddy covariance measurements of surface-atmosphere CO2 exchange is needed for data assimilation and inverse analyses to estimate model parameters, validation of ecosystem models against flux data, as well as multi-site synthesis activities (e.g., regional to continental integration) and policy decision-making. While model residuals (mismatch between fitted model predictions and measured fluxes) can potentially be analyzed to infer data uncertainties, the resulting uncertainty estimates may be sensitive to the particular model chosen. Here we use 10 site-years of data from the CarboEurope program, and compare the statistical properties of the inferred random flux measurement error calculated first using residuals from five different models, and secondly using paired observations made under similar environmental conditions. Spectral analysis of the model predictions indicated greater persistence (i.e., autocorrelation or memory) compared to the measured values. Model residuals exhibited weaker temporal correlation, but were not uncorrelated white noise. Random flux measurement uncertainty, expressed as a standard deviation, was found to vary predictably in relation to the expected magnitude of the flux, in a manner that was nearly identical (for negative, but not positive, fluxes) to that reported previously for forested sites. Uncertainty estimates were generally comparable whether the uncertainty was inferred from model residuals or paired observations, although the latter approach resulted in somewhat smaller estimates. Higher order moments (e.g., skewness and kurtosis) suggested that for fluxes close to zero, the measurement error is commonly skewed and leptokurtic. Skewness could not be evaluated using the paired observation approach, because differencing of paired measurements resulted in a symmetric distribution of the inferred error. Patterns were robust and not especially sensitive to the model used, although more flexible models, which did not impose a particular functional form on relationships between environmental drivers and modeled fluxes, appeared to give the best results. We conclude that evaluation of flux measurement errors from model residuals is a viable alternative to the standard paired observation approach.
Quality control of CarboEurope flux data - Part 1: Coupling footprint analyses with flux data quality assessment to evaluate sites in forest ecosystems
Gockede, M. ; Foken, T. ; Aubinet, M. ; Aurela, M. ; Banza, J. ; Bernhofer, C. ; Bonnefonds, J.M. ; Brunet, Y. ; Carrara, A. ; Clement, R. ; Dellwik, E. ; Elbers, J.A. ; Eugster, W. ; Fuhrer, J. ; Granier, A. ; Grunwald, T. ; Heinsch, B. ; Janssens, I.A. ; Knohl, A. ; Koeble, R. ; Laurila, T. ; Longdoz, B. ; Manca, G. ; Marek, M. ; Markkanen, T. ; Mateus, J. ; Matteucci, G. ; Mauder, M. ; Migliavacca, M. ; Minerbi, S. ; Moncrieff, J. ; Montagnani, L. ; Moors, E.J. ; Ourcival, J.M. ; Papale, D. ; Pereira, J.M. ; Pilegaard, K. ; Pita, G. ; Rambal, S. ; Rebmann, C. ; Rodrigues, A. ; Rotenberg, E. ; Sanz, M.J. ; Sedlak, P. ; Seufert, G. ; Siebicke, L. ; Soussana, J.F. ; Valentini, R. ; Vesala, T. ; Verbeeck, H. ; Yakir, D. - \ 2008
Biogeosciences 5 (2008)2. - ISSN 1726-4170 - p. 433 - 450.
warmtestroming - eddy-covariantie - gegevensanalyse - ecosystemen - bossen - atmosferische grenslaag - heat flow - eddy covariance - data analysis - ecosystems - forests - atmospheric boundary-layer - eddy covariance measurements - water-vapor - boundary-layer - heat-flux - turbulence statistics - correlation systems - stochastic-models - sonic anemometer - surface fluxes - carbon-dioxide
We applied a site evaluation approach combining Lagrangian Stochastic footprint modeling with a quality assessment approach for eddy-covariance data to 25 forested sites of the CarboEurope-IP network. The analysis addresses the spatial representativeness of the flux measurements, instrumental effects on data quality, spatial patterns in the data quality, and the performance of the coordinate rotation method. Our findings demonstrate that application of a footprint filter could strengthen the CarboEurope-IP flux database, since only one third of the sites is situated in truly homogeneous terrain. Almost half of the sites experience a significant reduction in eddy-covariance data quality under certain conditions, though these effects are mostly constricted to a small portion of the dataset. Reductions in data quality of the sensible heat flux are mostly induced by characteristics of the surrounding terrain, while the latent heat flux is subject to instrumentation-related problems. The Planar-Fit coordinate rotation proved to be a reliable tool for the majority of the sites using only a single set of rotation angles. Overall, we found a high average data quality for the CarboEurope-IP network, with good representativeness of the measurement data for the specified target land cover types.
Impacts of topography and land degradation on the sea breeze over eastern Spain
Miao, J.F. ; Kroon, L.J.M. ; Vilà-Guerau de Arellano, J. ; Holtslag, A.A.M. - \ 2003
Meteorology and Atmospheric Physics 84 (2003). - ISSN 0177-7971 - p. 157 - 170.
mesoscale circulations - coastal environment - numerical-model - surface fluxes - soil-moisture - lake breeze - james-bay - vegetation - heat - desertification
A three-dimensional non-hydrostatic atmospheric model RAMS, version3b, is used to examine the impact of complex topography on the sea breeze under heterogeneous and degradation land use characteristics. In the study, it is shown that topography plays an important role in the sea-breeze circulation by aligning the sea breeze front to the coastline and locating the convergence zones close to the mountain range. When the sea breeze is coupled with the upslope wind, the sea-breeze circulation is strengthened by the topography. Sensitivity analyses are carried out to determine the influence of vegetation and soil moisture, i.e., land surface modifications, to this thermally driven flow. Land degradation results in an enhanced sea-breeze circulation which is characterized by a stronger onshore flow, a stronger return current, a larger updraft velocity associated with the sea-breeze front and further inland penetration. Other important features are a deeper sea-breeze depth, a larger downdraft velocity behind the sea-breeze front, and a longer offshore extent. The results also show how land changes modify the sea breeze temporal evolution resulting in an earlier onset and later end. The study stresses the convenience of using three-dimensional models with detailed land surface information to model the sea breeze in complex terrain where land use is rapidly modified.
Representing the atmospheric boundary layer in climate models of intermediate compexity
Ronda, R.J. ; Haarsma, R.J. ; Holtslag, A.A.M. - \ 2003
Climate Dynamics 21 (2003)3-4. - ISSN 0930-7575 - p. 327 - 335.
general-circulation model - surface fluxes - part i - parameterization - simulations - turbulence - land - diffusion - schemes - energy
In this study the role of atmospheric boundary layer schemes in climate models is investigated. Including a boundary layer scheme in an Earth system model of intermediate complexity (EMIC) produces only minor differences in the estimated global distribution of sensible and latent heat fluxes over land (upto about 15% of the net radiation at the surface). However, neglecting of boundary layer processes, such as the development of a well-mixed layer over land or the impact of stability on the exchange coefficient in the surface layer, leads to erroneous surface temperatures, especially in convective conditions with low wind speeds. As these conditions occur frequently, introducing a boundary layer scheme in an EMIC gives reductions in June-July-August averaged surface temperature of 1¿2 °C in wet areas, to 5¿7 °C in desert areas. Even a relatively simple boundary layer scheme provides reasonable estimates of the surface fluxes and surface temperatures. Detailed schemes that solve explicitly the turbulent fluxes within the boundary layer are only required when vertical profiles of potential temperature are needed.