Present and future atmospheric blocking and its impact on European mean and extreme climate

Atmospheric blocking plays an important role in the mid-latitude climate variability and can be responsible for anomalous mean and/or extreme climate. In this study, a potential vorticity based blocking indicator is used to investigate the representation of Euro-Atlantic atmospheric blocking events in the ECHAM5/MPI-OM climate model. The impact of blocking events on present and future mean and extreme climate is studied by means of composite maps and correlation analyses. In comparison to ERA-40 re-analysis, the model represents the blocking frequency and seasonal distribution well. We show that European blocking events have a sustained influence particularly on anomalous cold winter temperatures in Europe. In a future climate, the blocking frequency is slightly diminished but the influence on the European winter climate remains robust. Due to a northeastward shift of the blocking pattern and an increase in maximum blocking duration, cold winter temperature extremes can still be expected in a future climat

Linkage of atmospheric blocks and synoptic-scale Rossby waves: a climatological analysis

The link between atmospheric blocking and propagating and breaking synoptic-scale Rossby waves (termed PV streamers) are explored for the climatological period 1958–2002, using the ERA-40 re-analysis data. To this end, potential vorticity (PV) based climatologies of blocking and breaking waves are used, and features of the propagating waves is extracted from Hovm¨oller diagrams. The analyses cover the Northern Hemisphere during winter, and they are carried out for the Atlantic and Pacific basins separately. The results show statistically significant wave precursor signals, up to 5 d prior to the blocking onset. In the Atlantic, the precursor signal takes the form of a coherent wave train, emanating approximately 110◦ upstream of the blocking location. In the Pacific, a single long-lived (10 d) northerly velocity signal preludes the blocking onset. A spatial analysis is conducted of the location, frequency and form of breaking synoptic-scale Rossby waves, prior to the onset, during the lifetime and after the blocking decay. It reveals that cyclonic streamers are present to the southwest and anticyclonic streamers to the south and southeast, approximately 43% (36%) of the time in the Atlantic (Pacific) basin, and this is significantly above a climatological distribution.ISSN:0280-6495ISSN:1600-087

Towards implementing climate services in Peru – The project CLIMANDES

CLIMANDES is a pilot twinning project between the National Weather Services of Peru and Switzerland (SENAMHI and MeteoSwiss), developed within the Global Framework for Climate Services of the World Meteorological Organization (WMO). Split in two modules, CLIMANDES aims at improving education in meteorology and climatology in support of the WMO Regional Training Center in Peru, and introducing user-tailored climate services in two pilot regions in the Peruvian Andes. Four areas were prioritized in the first phase of CLIMANDES lasting from 2012 to 2015 to introduce climate services in Peru. A demand study identified the user needs of climate services and showed that climate information must be reliable, of high-quality, and precise. The information should be accessible and timely, understandable and applicable for the users’ specific needs. Second, the quality of climate data was enhanced through the establishment of quality control and homogenization procedures at SENAMHI. Specific training and application of the implemented methods at stations in the pilot regions was promoted to ensure the sustainability of the work. Third, the specific work on climate data enabled the creation of a webpage to disseminate climate indicators among users. The forth priority of the project enhanced the broad communication strategy of SENAMHI through creation of a specialized network of journalists, diverse climate forums, and the establishment of a user database. The efforts accomplished within CLIMANDES improved the quality of the climate services provided by SENAMHI. The project hence contributed successfully to higher awareness and higher confidence in the climate information by SENAMHI.Por pare

The influence of station density on climate data homogenization

Relative homogenization methods assume that measurements of nearby stations experience similar climate signals and rely therefore on dense station networks with high-temporal correlations. In developing countries such as Peru, however, networks often suffer from low-station density. The aim of this study is to quantify the influence of network density on homogenization. To this end, the homogenization method HOMER was applied to an artificially thinned Swiss network. Four homogenization experiments, reflecting different homogenization approaches, were examined. Such approaches include diverse levels of interaction of the homogenization operators with HOMER, and different application of metadata. To evaluate the performance of HOMER in the sparse networks, a reference series was built by applying HOMER under the best possible conditions. Applied in completely automatic mode, HOMER decreases the reliability of temperature records. Therefore, automatic use of HOMER is not recommended. If HOMER is applied in interactive mode, the reliability of temperature and precipitation data may be increased in sparse networks. However, breakpoints must be inserted conservatively. Information from metadata should be used only to determine the exact timing of statistically detected breaks. Insertion of additional breakpoints based solely on metadata may lead to harmful corrections due to the high noise in sparse networks

Global climatologies of Eulerian and Lagrangian flow features based on ERA-Interim

This paper introduces a newly compiled set of feature-based climatologies identified from ERA-Interim (1979–2014). Two categories of flow features are considered: (i) Eulerian climatologies of jet streams, tropopause folds, surface fronts, cyclones and anticyclones, blocks, and potential vorticity streamers and cutoffs and (ii) Lagrangian climatologies, based on a large ensemble of air parcel trajectories, of stratosphere–troposphere exchange, warm conveyor belts, and tropical moisture exports. Monthly means of these feature climatologies are openly available at the ETH Zürich web page (http://eraiclim.ethz.ch) and are annually updated. Datasets at higher resolution can be obtained from the authors on request. These feature climatologies allow studying the frequency, variability, and trend of atmospheric phenomena and their interrelationships across temporal scales. To illustrate the potential of this dataset, boreal winter climatologies of selected features are presented and, as a first application, the very unusual Northern Hemispheric winter of 2009/10 is identified as the season when most of the considered features show maximum deviations from climatology. The second application considers dry winters in the western United States and reveals fairly localized anomalies in the eastern North Pacific of enhanced blocking and surface anticyclones and reduced cyclones

Towards implementing climate services in Peru – The project CLIMANDES

AbstractCLIMANDES is a pilot twinning project between the National Weather Services of Peru and Switzerland (SENAMHI and MeteoSwiss), developed within the Global Framework for Climate Services of the World Meteorological Organization (WMO). Split in two modules, CLIMANDES aims at improving education in meteorology and climatology in support of the WMO Regional Training Center in Peru, and introducing user-tailored climate services in two pilot regions in the Peruvian Andes.Four areas were prioritized in the first phase of CLIMANDES lasting from 2012 to 2015 to introduce climate services in Peru. A demand study identified the user needs of climate services and showed that climate information must be reliable, of high-quality, and precise. The information should be accessible and timely, understandable and applicable for the users’ specific needs. Second, the quality of climate data was enhanced through the establishment of quality control and homogenization procedures at SENAMHI. Specific training and application of the implemented methods at stations in the pilot regions was promoted to ensure the sustainability of the work. Third, the specific work on climate data enabled the creation of a webpage to disseminate climate indicators among users. The forth priority of the project enhanced the broad communication strategy of SENAMHI through creation of a specialized network of journalists, diverse climate forums, and the establishment of a user database.The efforts accomplished within CLIMANDES improved the quality of the climate services provided by SENAMHI. The project hence contributed successfully to higher awareness and higher confidence in the climate information by SENAMHI

Climate scenarios for Switzerland CH2018 - approach and implications

To make sound decisions in the face of climate change, government agencies, policymakers and private stakeholders require suitable climate information on local to regional scales. In Switzerland, the development of climate change scenarios is strongly linked to the climate adaptation strategy of the Confederation. The current climate scenarios for Switzerland CH2018 - released in form of six user-oriented products - were the result of an intensive collaboration between academia and administration under the umbrella of the National Centre for Climate Services (NCCS), accounting for user needs and stakeholder dialogues from the beginning. A rigorous scientific concept ensured consistency throughout the various analysis steps of the EURO-CORDEX projections and a common procedure on how to extract robust results and deal with associated uncertainties. The main results show that Switzerland?s climate will face dry summers, heavy precipitation, more hot days and snow-scarce winters. Approximately half of these changes could be alleviated by mid-century through strong global mitigation efforts. A comprehensive communication concept ensured that the results were rolled out and distilled in specific user-oriented communication measures to increase their uptake and to make them actionable. A narrative approach with four fictitious persons was used to communicate the key messages to the general public. Three years after the release, the climate scenarios have proven to be an indispensable information basis for users in climate adaptation and for downstream applications. Potential for extensions and updates has been identified since then and will shape the concept and planning of the next scenario generation in Switzerland

Climate Scenarios for Switzerland CH2018 – Approach and Implications

To make sound decisions in the face of climate change, government agencies, policymakers and private stakeholders require suitable climate information on local to regional scales. In Switzerland, the development of climate change scenarios is strongly linked to the climate adaptation strategy of the Confederation. The current climate scenarios for Switzerland CH2018 - released in form of six user-oriented products - were the result of an intensive collaboration between academia and administration under the umbrella of the National Centre for Climate Services (NCCS), accounting for user needs and stakeholder dialogues from the beginning. A rigorous scientific concept ensured consistency throughout the various analysis steps of the EURO-CORDEX projections and a common procedure on how to extract robust results and deal with associated uncertainties. The main results show that Switzerland’s climate will face dry summers, heavy precipitation, more hot days and snow-scarce winters. Approximately half of these changes could be alleviated by mid-century through strong global mitigation efforts. A comprehensive communication concept ensured that the results were rolled out and distilled in specific user-oriented communication measures to increase their uptake and to make them actionable. A narrative approach with four fictitious persons was used to communicate the key messages to the general public. Three years after the release, the climate scenarios have proven to be an indispensable information basis for users in climate adaptation and for downstream applications. Potential for extensions and updates has been identified since then and will shape the concept and planning of the next scenario generation in Switzerland

The variable link between PNA and NAO in observations and in multi-century CGCM simulations

The link between the Pacific/North American pattern (PNA) and the North Atlantic Oscillation (NAO) is investigated in reanalysis data (NCEP, ERA40) and multi-century CGCM runs for present day climate using three versions of the ECHAM model. PNA and NAO patterns and indices are determined via rotated principal component analysis on monthly mean 500 hPa geopotential height fields using the varimax criteria. On average, the multi-century CGCM simulations show a significant anti-correlation between PNA and NAO. Further, multi-decadal periods with significantly enhanced (high anti-correlation, active phase) or weakened (low correlations, inactive phase) coupling are found in all CGCMs. In the simulated active phases, the storm track activity near Newfoundland has a stronger link with the PNA variability than during the inactive phases. On average, the reanalysis datasets show no significant anti-correlation between PNA and NAO indices, but during the sub-period 1973–1994 a significant anti-correlation is detected, suggesting that the present climate could correspond to an inactive period as detected in the CGCMs. An analysis of possible physical mechanisms suggests that the link between the patterns is established by the baroclinic waves forming the North Atlantic storm track. The geopotential height anomalies associated with negative PNA phases induce an increased advection of warm and moist air from the Gulf of Mexico and cold air from Canada. Both types of advection contribute to increase baroclinicity over eastern North America and also to increase the low level latent heat content of the warm air masses. Thus, growth conditions for eddies at the entrance of the North Atlantic storm track are enhanced. Considering the average temporal development during winter for the CGCM, results show an enhanced Newfoundland storm track maximum in the early winter for negative PNA, followed by a downstream enhancement of the Atlantic storm track in the subsequent months. In active (passive) phases, this seasonal development is enhanced (suppressed). As the storm track over the central and eastern Atlantic is closely related to the NAO variability, this development can be explained by the shift of the NAO index to more positive values