Mark Liniger - Academia.edu (original) (raw)

Papers by Mark Liniger

Journal of geophysical research. Atmospheres : JGR, Jan 16, 2015

Climate indices help to describe the past, present, and the future climate. They are usually clos... more Climate indices help to describe the past, present, and the future climate. They are usually closer related to possible impacts and are therefore more illustrative to users than simple climate means. Indices are often based on daily data series and thresholds. It is shown that the percentile-based thresholds are sensitive to the method of computation, and so are the climatological daily mean and the daily standard deviation, which are used for bias corrections of daily climate model data. Sample size issues of either the observed reference period or the model data lead to uncertainties in these estimations. A large number of past ensemble seasonal forecasts, called hindcasts, is used to explore these sampling uncertainties and to compare two different approaches. Based on a perfect model approach it is shown that a fitting approach can improve substantially the estimates of daily climatologies of percentile-based thresholds over land areas, as well as the mean and the variability. T...

A study is undertaken of the substructure of an upper-level potential-vorticity streamer that app... more A study is undertaken of the substructure of an upper-level potential-vorticity streamer that approached the European Alps during the eld phase of the Mesoscale Alpine Programme (MAP). The diagnosis is based upon a Lagrangian Forward Projection (LFP) technique which can provide a spatial re nement of the operational European Centre for Medium-Range Weather Forecasts analysis elds. The reconstructed elds capture several notable ne-scale features of the streamer's structure that include spiral arms of a vortex-like feature and a richly structured western ank to the streamer comprising a deep primary fold surmounted by a signi cant secondary fold with an intermediate distinctive striation that extends back into the stratosphere.

Journal of Geophysical Research-Atmospheres, 2004

1] The distribution of extratropical potential vorticity (PV) on isentropic surfaces that transec... more 1] The distribution of extratropical potential vorticity (PV) on isentropic surfaces that transect the tropopause is a key feature of planetary-scale teleconnection patterns, synoptic-scale weather systems, and mesoscale stratosphere-troposphere exchange. Here a Northern Hemisphere January and July climatology is presented for the mean and variability patterns of the PV using the so-called European Centre for Medium-Range Weather Forecasts reanalysis-15 (ERA-15) data set. It is derived taking into account the strong seasonal cycle of the tropopause height and the sharp quasi-latitudinal gradient of PV on the isentropic surfaces together with the accompanying bimodality in the scale and amplitude of positive and negative anomalies. The bimodality is both emphasized and circumvented by comparing conventional standard deviation measures of the variability with those of separate depictions of the probability density function structures of positive and negative anomalies. It is shown that in winter the zonal heterogeneity is pronounced and the variability (e.g., storm track) patterns exhibit a rich spatial structure with marked differences between the Pacific and Atlantic. In contrast, in summer the heterogeneity on the lower stratospheric portion of the isentropic surfaces is much weaker, but there remain regions of high variability over oceanic regions on the tropospheric portion of the surfaces. The results relate directly to the structure and dynamics of storm tracks and their spatial and seasonal variation.

Journal of Climate, 2005

The ranked probability skill score (RPSS) is a widely used measure to quantify the skill of ensem... more The ranked probability skill score (RPSS) is a widely used measure to quantify the skill of ensemble forecasts. The underlying score is defined by the quadratic norm and is comparable to the mean squared error (mse) but it is applied in probability space. It is sensitive to the shape and the shift of the predicted probability distributions. However, the RPSS

International Journal of Climatology, 2006

This study discusses problems of the concept of normal period-based anomalies arising from climat... more This study discusses problems of the concept of normal period-based anomalies arising from climate variability and ongoing climate change. The widely used WMO 1961WMO -1990 standard normal period is compared to other consecutive 30-year normal periods in detail. Focus is given to the temperature distribution in Switzerland and on the European continent. In these regions, the temperature trend of the last decades led to an unusually high number of months with positive temperature anomalies relative to the WMO 61-90 standard normal period. Swiss anomalies based on the 61-90 normal are up to 1.25 K higher than those based on the Latest 30-years Running Normal (LRN). The probability to observe a positive temperature anomaly with respect to the 61-90 normal increased from 50% to near 80% for certain months of the year. Compared to the LRN, this change is statistically significant for 7 out of the 12 months on the 95% level. The strongest signal can be found for the summer months, whereas temperatures in fall do not show any trends. Similar results are found for more than 90% of the European continental area. For most regions, 2-5 are statistically inconsistent with the 61-90 distribution. For southern France, parts of Spain and southern Scandinavia even 7-9 months are inconsistent.

Journal of Geophysical Research-Atmospheres, 2006

ABSTRACT The 31 stations in the Global Positioning System (GPS) network of Switzerland span an al... more ABSTRACT The 31 stations in the Global Positioning System (GPS) network of Switzerland span an altitude range of 330 to 3584 m. The highest station in the network, Jungfraujoch, suffers from a constant negative bias in the Integrated Water Vapor (IWV) due to a protective radome. We compared Jungfraujoch GPS IWV measurements with coincident Precision Filter Radiometer (PFR) observations and showed that the bias in the GPS is fairly constant with respect to the time of year and to the PFR IWV value. A correction was developed for the GPS data and validated by comparison with coincident Raman lidar observations. The IWV observations from nine GPS stations, including Jungfraujoch, were then compared with the IWV field of the ECMWF 40 year reanalysis (ERA40) data. Altitude differences between the ERA40 surface level and the GPS stations resulted, as expected, in a positive bias in the ERA40 IWV. A fairly linear relationship, with an intercept of −0.3 mm, was found between this bias and the difference between the ERA40 surface pressure and the surface pressure at the GPS station. The ERA40 reanalysis captured water vapor variations on timescales of several days very well, as evidenced by an r2 correlation greater than 0.9 where the altitude difference between ERA40 and the GPS station was less than 1000 m. A comparison between ERA40 and GPS at Davos showed that the reanalysis underestimates IWV during winter temperature inversions.

Monthly Weather Review, 2007

The Brier skill score (BSS) and the ranked probability skill score (RPSS) are widely used measure... more The Brier skill score (BSS) and the ranked probability skill score (RPSS) are widely used measures to describe the quality of categorical probabilistic forecasts. They quantify the extent to which a forecast strategy improves predictions with respect to a (usually climatological) reference forecast. The BSS can thereby be regarded as the special case of an RPSS with two forecast categories. From the work of Müller et al., it is known that the RPSS is negatively biased for ensemble prediction systems with small ensemble sizes, and that a debiased version, the RPSS D , can be obtained quasi empirically by random resampling from the reference forecast. In this paper, an analytical formula is derived to directly calculate the RPSS bias correction for any ensemble size and combination of probability categories, thus allowing an easy implementation of the RPSS D . The correction term itself is identified as the "intrinsic unreliability" of the ensemble prediction system. The performance of this new formulation of the RPSS D is illustrated in two examples. First, it is applied to a synthetic random white noise climate, and then, using the ECMWF Seasonal Forecast System 2, to seasonal predictions of near-surface temperature in several regions of different predictability. In both examples, the skill score is independent of ensemble size while the associated confidence thresholds decrease as the number of ensemble members and forecast/observation pairs increase.

Geophysical Research Letters, 2007

Monthly Weather Review, 2007

This note describes how the widely used Brier and ranked probability skill scores (BSS and RPSS, ... more This note describes how the widely used Brier and ranked probability skill scores (BSS and RPSS, respectively) can be correctly applied to quantify the potential skill of probabilistic multimodel ensemble forecasts. It builds upon the study of Weigel et al. where a revised RPSS, the so-called discrete ranked probability skill score (RPSS D ), was derived, circumventing the known negative bias of the RPSS for small ensemble sizes. Since the BSS is a special case of the RPSS, a debiased discrete Brier skill score (BSS D ) could be formulated in the same way. Here, the approach of Weigel et al., which so far was only applicable to single model ensembles, is generalized to weighted multimodel ensemble forecasts. By introducing an "effective ensemble size" characterizing the multimodel, the new generalized RPSS D can be expressed such that its structure becomes equivalent to the single model case. This is of practical importance for multimodel assessment studies, where the consequences of varying effective ensemble size need to be clearly distinguished from the true benefits of multimodel combination. The performance of the new generalized RPSS D formulation is illustrated in examples of weighted multimodel ensemble forecasts, both in a synthetic random forecasting context, and with real seasonal forecasts of operational models. A central conclusion of this study is that, for small ensemble sizes, multimodel assessment studies should not only be carried out on the basis of the classical RPSS, since true changes in predictability may be hidden by bias effects-a deficiency that can be overcome with the new generalized RPSS D .

Monthly Weather Review, 2008

Monthly Weather Review, 2009

... 2005; Feddersen and Andersen 2005), but the conceptual differences between a reliability corr... more ... 2005; Feddersen and Andersen 2005), but the conceptual differences between a reliability correction by MMEC and a reliability correction ... quantifies how consistent the forecast probabilities are with the relative frequencies of the observed outcomes (eg, Mason and Stephenson ...

Journal of Geophysical Research-Atmospheres, 2010

1] The coarse spacing of automatic rain gauges complicates near-real-time spatial analyses of pre... more 1] The coarse spacing of automatic rain gauges complicates near-real-time spatial analyses of precipitation. We test the possibility of improving such analyses by considering, in addition to the in situ measurements, the spatial covariance structure inferred from past observations with a denser network. To this end, a statistical reconstruction technique, reduced space optimal interpolation (RSOI), is applied over Switzerland, a region of complex topography. RSOI consists of two main parts. First, principal component analysis (PCA) is applied to obtain a reduced space representation of gridded high-resolution precipitation fields available for a multiyear calibration period in the past. Second, sparse real-time rain gauge observations are used to estimate the principal component scores and to reconstruct the precipitation field. In this way, climatological information at higher resolution than the near-real-time measurements is incorporated into the spatial analysis. PCA is found to efficiently reduce the dimensionality of the calibration fields, and RSOI is successful despite the difficulties associated with the statistical distribution of daily precipitation (skewness, dry days). Examples and a systematic evaluation show substantial added value over a simple interpolation technique that uses near-real-time observations only. The benefit is particularly strong for larger-scale precipitation and prominent topographic effects. Small-scale precipitation features are reconstructed at a skill comparable to that of the simple technique. Stratifying the reconstruction method by the types of weather type classifications yields little added skill. Apart from application in near real time, RSOI may also be valuable for enhancing instrumental precipitation analyses for the historic past when direct observations were sparse.

Monthly Weather Review, 2010

... Corresponding author address: Felix Fundel, MeteoSchweiz, Kraehbuehlstrasse 58, 8044 Zurich, ... more ... Corresponding author address: Felix Fundel, MeteoSchweiz, Kraehbuehlstrasse 58, 8044 Zurich, Switzerland. Email: felix.fundel@meteoswiss.ch. 1. Introduction. ... 2004, 2006; Hamill and Whitaker 2006; Wilks and Hamill 2007; Hamill et al. 2008; Hagedorn et al. 2008). ...

Journal of Agricultural Science, 2011

Journal of Geophysical Research-Biogeosciences, 2011

1] Simulations of the global water and carbon cycle are sensitive to the model representation of ... more 1] Simulations of the global water and carbon cycle are sensitive to the model representation of vegetation phenology. Current phenology models are empirical, and few predict both phenological timing and leaf state. Our previous study demonstrated how satellite data assimilation employing an Ensemble Kalman Filter yields realistic phenological model parameters for several ecosystem types. In this study the data assimilation framework is extended to global scales using a subgrid-scale representation of plant functional types (PFTs) and elevation classes. A reanalysis of vegetation phenology for 256 globally distributed regions is performed using 10 years of Moderate Resolution Imaging Spectroradiometer (MODIS) fraction of photosynthetically active radiation (FPAR) absorbed by vegetation and leaf area index (LAI) data. The 9 · 10 8 quality screened observations (corresponding to <1% of the globally available MODIS data) successfully constrain a posterior PFT-dependent phenological parameter set. It reduces the global FPAR and LAI prediction error to 20.6% and 14.8%, respectively, compared to the prior prediction error. A 50 year long (1960-2009) daily 1°× 1°global phenology data set with a mean FPAR and LAI prediction error of 0.065 (−) and 0.34 (m 2 m −2 ) is generated. Temperate phenology is best explained by a combination of light and temperature. Tropical evergreen phenology is found to be largely insensitive to moisture and light variations. Boreal phenology can be accurately predicted from local to global scales, while temperate and mediterranean landscapes might benefit from a better subgrid-scale PFT classification or from a more complex canopy radiative transfer model.

Quarterly Journal of the Royal Meteorological Society, 2002

Dynamical aspects of the life cycle of the winter storm 'Lothar' (24-26 December 1999) are invest... more Dynamical aspects of the life cycle of the winter storm 'Lothar' (24-26 December 1999) are investigated with the aid of the European Centre for Medium-Range Weather Forecasts analysis data and mesoscale model simulations. Neither of these datasets capture the full amplitude of the observed extreme pressure fall and surface wind speeds, but they do help identify a range of key dynamical and physical features that characterize the development of this unusual event. The analysis and interpretation is primarily based upon the evolution of the lower-and upper-level potential vorticity (PV) eld complemented by three-dimensional trajectory calculations.

Quarterly Journal of the Royal Meteorological Society, 2008

Journal of geophysical research. Atmospheres : JGR, Jan 16, 2015

Climate indices help to describe the past, present, and the future climate. They are usually clos... more Climate indices help to describe the past, present, and the future climate. They are usually closer related to possible impacts and are therefore more illustrative to users than simple climate means. Indices are often based on daily data series and thresholds. It is shown that the percentile-based thresholds are sensitive to the method of computation, and so are the climatological daily mean and the daily standard deviation, which are used for bias corrections of daily climate model data. Sample size issues of either the observed reference period or the model data lead to uncertainties in these estimations. A large number of past ensemble seasonal forecasts, called hindcasts, is used to explore these sampling uncertainties and to compare two different approaches. Based on a perfect model approach it is shown that a fitting approach can improve substantially the estimates of daily climatologies of percentile-based thresholds over land areas, as well as the mean and the variability. T...

A study is undertaken of the substructure of an upper-level potential-vorticity streamer that app... more A study is undertaken of the substructure of an upper-level potential-vorticity streamer that approached the European Alps during the eld phase of the Mesoscale Alpine Programme (MAP). The diagnosis is based upon a Lagrangian Forward Projection (LFP) technique which can provide a spatial re nement of the operational European Centre for Medium-Range Weather Forecasts analysis elds. The reconstructed elds capture several notable ne-scale features of the streamer's structure that include spiral arms of a vortex-like feature and a richly structured western ank to the streamer comprising a deep primary fold surmounted by a signi cant secondary fold with an intermediate distinctive striation that extends back into the stratosphere.

Journal of Geophysical Research-Atmospheres, 2004

1] The distribution of extratropical potential vorticity (PV) on isentropic surfaces that transec... more 1] The distribution of extratropical potential vorticity (PV) on isentropic surfaces that transect the tropopause is a key feature of planetary-scale teleconnection patterns, synoptic-scale weather systems, and mesoscale stratosphere-troposphere exchange. Here a Northern Hemisphere January and July climatology is presented for the mean and variability patterns of the PV using the so-called European Centre for Medium-Range Weather Forecasts reanalysis-15 (ERA-15) data set. It is derived taking into account the strong seasonal cycle of the tropopause height and the sharp quasi-latitudinal gradient of PV on the isentropic surfaces together with the accompanying bimodality in the scale and amplitude of positive and negative anomalies. The bimodality is both emphasized and circumvented by comparing conventional standard deviation measures of the variability with those of separate depictions of the probability density function structures of positive and negative anomalies. It is shown that in winter the zonal heterogeneity is pronounced and the variability (e.g., storm track) patterns exhibit a rich spatial structure with marked differences between the Pacific and Atlantic. In contrast, in summer the heterogeneity on the lower stratospheric portion of the isentropic surfaces is much weaker, but there remain regions of high variability over oceanic regions on the tropospheric portion of the surfaces. The results relate directly to the structure and dynamics of storm tracks and their spatial and seasonal variation.

Journal of Climate, 2005

The ranked probability skill score (RPSS) is a widely used measure to quantify the skill of ensem... more The ranked probability skill score (RPSS) is a widely used measure to quantify the skill of ensemble forecasts. The underlying score is defined by the quadratic norm and is comparable to the mean squared error (mse) but it is applied in probability space. It is sensitive to the shape and the shift of the predicted probability distributions. However, the RPSS

International Journal of Climatology, 2006

This study discusses problems of the concept of normal period-based anomalies arising from climat... more This study discusses problems of the concept of normal period-based anomalies arising from climate variability and ongoing climate change. The widely used WMO 1961WMO -1990 standard normal period is compared to other consecutive 30-year normal periods in detail. Focus is given to the temperature distribution in Switzerland and on the European continent. In these regions, the temperature trend of the last decades led to an unusually high number of months with positive temperature anomalies relative to the WMO 61-90 standard normal period. Swiss anomalies based on the 61-90 normal are up to 1.25 K higher than those based on the Latest 30-years Running Normal (LRN). The probability to observe a positive temperature anomaly with respect to the 61-90 normal increased from 50% to near 80% for certain months of the year. Compared to the LRN, this change is statistically significant for 7 out of the 12 months on the 95% level. The strongest signal can be found for the summer months, whereas temperatures in fall do not show any trends. Similar results are found for more than 90% of the European continental area. For most regions, 2-5 are statistically inconsistent with the 61-90 distribution. For southern France, parts of Spain and southern Scandinavia even 7-9 months are inconsistent.

Journal of Geophysical Research-Atmospheres, 2006

ABSTRACT The 31 stations in the Global Positioning System (GPS) network of Switzerland span an al... more ABSTRACT The 31 stations in the Global Positioning System (GPS) network of Switzerland span an altitude range of 330 to 3584 m. The highest station in the network, Jungfraujoch, suffers from a constant negative bias in the Integrated Water Vapor (IWV) due to a protective radome. We compared Jungfraujoch GPS IWV measurements with coincident Precision Filter Radiometer (PFR) observations and showed that the bias in the GPS is fairly constant with respect to the time of year and to the PFR IWV value. A correction was developed for the GPS data and validated by comparison with coincident Raman lidar observations. The IWV observations from nine GPS stations, including Jungfraujoch, were then compared with the IWV field of the ECMWF 40 year reanalysis (ERA40) data. Altitude differences between the ERA40 surface level and the GPS stations resulted, as expected, in a positive bias in the ERA40 IWV. A fairly linear relationship, with an intercept of −0.3 mm, was found between this bias and the difference between the ERA40 surface pressure and the surface pressure at the GPS station. The ERA40 reanalysis captured water vapor variations on timescales of several days very well, as evidenced by an r2 correlation greater than 0.9 where the altitude difference between ERA40 and the GPS station was less than 1000 m. A comparison between ERA40 and GPS at Davos showed that the reanalysis underestimates IWV during winter temperature inversions.

Monthly Weather Review, 2007

The Brier skill score (BSS) and the ranked probability skill score (RPSS) are widely used measure... more The Brier skill score (BSS) and the ranked probability skill score (RPSS) are widely used measures to describe the quality of categorical probabilistic forecasts. They quantify the extent to which a forecast strategy improves predictions with respect to a (usually climatological) reference forecast. The BSS can thereby be regarded as the special case of an RPSS with two forecast categories. From the work of Müller et al., it is known that the RPSS is negatively biased for ensemble prediction systems with small ensemble sizes, and that a debiased version, the RPSS D , can be obtained quasi empirically by random resampling from the reference forecast. In this paper, an analytical formula is derived to directly calculate the RPSS bias correction for any ensemble size and combination of probability categories, thus allowing an easy implementation of the RPSS D . The correction term itself is identified as the "intrinsic unreliability" of the ensemble prediction system. The performance of this new formulation of the RPSS D is illustrated in two examples. First, it is applied to a synthetic random white noise climate, and then, using the ECMWF Seasonal Forecast System 2, to seasonal predictions of near-surface temperature in several regions of different predictability. In both examples, the skill score is independent of ensemble size while the associated confidence thresholds decrease as the number of ensemble members and forecast/observation pairs increase.

Geophysical Research Letters, 2007

Monthly Weather Review, 2007

This note describes how the widely used Brier and ranked probability skill scores (BSS and RPSS, ... more This note describes how the widely used Brier and ranked probability skill scores (BSS and RPSS, respectively) can be correctly applied to quantify the potential skill of probabilistic multimodel ensemble forecasts. It builds upon the study of Weigel et al. where a revised RPSS, the so-called discrete ranked probability skill score (RPSS D ), was derived, circumventing the known negative bias of the RPSS for small ensemble sizes. Since the BSS is a special case of the RPSS, a debiased discrete Brier skill score (BSS D ) could be formulated in the same way. Here, the approach of Weigel et al., which so far was only applicable to single model ensembles, is generalized to weighted multimodel ensemble forecasts. By introducing an "effective ensemble size" characterizing the multimodel, the new generalized RPSS D can be expressed such that its structure becomes equivalent to the single model case. This is of practical importance for multimodel assessment studies, where the consequences of varying effective ensemble size need to be clearly distinguished from the true benefits of multimodel combination. The performance of the new generalized RPSS D formulation is illustrated in examples of weighted multimodel ensemble forecasts, both in a synthetic random forecasting context, and with real seasonal forecasts of operational models. A central conclusion of this study is that, for small ensemble sizes, multimodel assessment studies should not only be carried out on the basis of the classical RPSS, since true changes in predictability may be hidden by bias effects-a deficiency that can be overcome with the new generalized RPSS D .

Monthly Weather Review, 2008

Monthly Weather Review, 2009

... 2005; Feddersen and Andersen 2005), but the conceptual differences between a reliability corr... more ... 2005; Feddersen and Andersen 2005), but the conceptual differences between a reliability correction by MMEC and a reliability correction ... quantifies how consistent the forecast probabilities are with the relative frequencies of the observed outcomes (eg, Mason and Stephenson ...

Journal of Geophysical Research-Atmospheres, 2010

1] The coarse spacing of automatic rain gauges complicates near-real-time spatial analyses of pre... more 1] The coarse spacing of automatic rain gauges complicates near-real-time spatial analyses of precipitation. We test the possibility of improving such analyses by considering, in addition to the in situ measurements, the spatial covariance structure inferred from past observations with a denser network. To this end, a statistical reconstruction technique, reduced space optimal interpolation (RSOI), is applied over Switzerland, a region of complex topography. RSOI consists of two main parts. First, principal component analysis (PCA) is applied to obtain a reduced space representation of gridded high-resolution precipitation fields available for a multiyear calibration period in the past. Second, sparse real-time rain gauge observations are used to estimate the principal component scores and to reconstruct the precipitation field. In this way, climatological information at higher resolution than the near-real-time measurements is incorporated into the spatial analysis. PCA is found to efficiently reduce the dimensionality of the calibration fields, and RSOI is successful despite the difficulties associated with the statistical distribution of daily precipitation (skewness, dry days). Examples and a systematic evaluation show substantial added value over a simple interpolation technique that uses near-real-time observations only. The benefit is particularly strong for larger-scale precipitation and prominent topographic effects. Small-scale precipitation features are reconstructed at a skill comparable to that of the simple technique. Stratifying the reconstruction method by the types of weather type classifications yields little added skill. Apart from application in near real time, RSOI may also be valuable for enhancing instrumental precipitation analyses for the historic past when direct observations were sparse.

Monthly Weather Review, 2010

... Corresponding author address: Felix Fundel, MeteoSchweiz, Kraehbuehlstrasse 58, 8044 Zurich, ... more ... Corresponding author address: Felix Fundel, MeteoSchweiz, Kraehbuehlstrasse 58, 8044 Zurich, Switzerland. Email: felix.fundel@meteoswiss.ch. 1. Introduction. ... 2004, 2006; Hamill and Whitaker 2006; Wilks and Hamill 2007; Hamill et al. 2008; Hagedorn et al. 2008). ...

Journal of Agricultural Science, 2011

Journal of Geophysical Research-Biogeosciences, 2011

1] Simulations of the global water and carbon cycle are sensitive to the model representation of ... more 1] Simulations of the global water and carbon cycle are sensitive to the model representation of vegetation phenology. Current phenology models are empirical, and few predict both phenological timing and leaf state. Our previous study demonstrated how satellite data assimilation employing an Ensemble Kalman Filter yields realistic phenological model parameters for several ecosystem types. In this study the data assimilation framework is extended to global scales using a subgrid-scale representation of plant functional types (PFTs) and elevation classes. A reanalysis of vegetation phenology for 256 globally distributed regions is performed using 10 years of Moderate Resolution Imaging Spectroradiometer (MODIS) fraction of photosynthetically active radiation (FPAR) absorbed by vegetation and leaf area index (LAI) data. The 9 · 10 8 quality screened observations (corresponding to <1% of the globally available MODIS data) successfully constrain a posterior PFT-dependent phenological parameter set. It reduces the global FPAR and LAI prediction error to 20.6% and 14.8%, respectively, compared to the prior prediction error. A 50 year long (1960-2009) daily 1°× 1°global phenology data set with a mean FPAR and LAI prediction error of 0.065 (−) and 0.34 (m 2 m −2 ) is generated. Temperate phenology is best explained by a combination of light and temperature. Tropical evergreen phenology is found to be largely insensitive to moisture and light variations. Boreal phenology can be accurately predicted from local to global scales, while temperate and mediterranean landscapes might benefit from a better subgrid-scale PFT classification or from a more complex canopy radiative transfer model.

Quarterly Journal of the Royal Meteorological Society, 2002

Dynamical aspects of the life cycle of the winter storm 'Lothar' (24-26 December 1999) are invest... more Dynamical aspects of the life cycle of the winter storm 'Lothar' (24-26 December 1999) are investigated with the aid of the European Centre for Medium-Range Weather Forecasts analysis data and mesoscale model simulations. Neither of these datasets capture the full amplitude of the observed extreme pressure fall and surface wind speeds, but they do help identify a range of key dynamical and physical features that characterize the development of this unusual event. The analysis and interpretation is primarily based upon the evolution of the lower-and upper-level potential vorticity (PV) eld complemented by three-dimensional trajectory calculations.

Quarterly Journal of the Royal Meteorological Society, 2008