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  • 1
    Language: English
    In: Geophysical research letters, 2015-02-28, Vol.42 (4), p.1165-1172
    Description: Climate models project that heavy precipitation events intensify with climate change. It is generally accepted that extreme day‐long events will increase at a rate of about 6–7% per degree warming, consistent with the Clausius‐Clapeyron relation. However, recent studies suggest that subdaily (e.g., hourly) precipitation extremes may increase at about twice this rate. Conventional climate models are not suited to assess such events, due to the limited spatial resolution and the need to parametrize convective precipitation (i.e., thunderstorms and rain showers). Here we employ a convection‐resolving model using a horizontal grid spacing of 2.2 km across an extended region covering the Alps and its larger‐scale surrounding from northern Italy to northern Germany. Consistent with previous results, projections using a Representative Concentration Pathways version 8.5 greenhouse gas scenario reveal a significant decrease of mean summer precipitation. However, unlike previous studies, we find that both extreme day‐long and hour‐long precipitation events asymptotically intensify with the Clausius‐Clapeyron relation. Differences to previous studies might be due to the model or region considered, but we also show that it is inconsistent to extrapolate from present‐day precipitation scaling into the future. Key Point Extreme hourly precipitation intensifies with the Clausius‐Clapeyron scaling
    Subject(s): Clausius-Clapeyron scaling ; climate simulations ; convection-resolving model ; hourly precipitation
    ISSN: 0094-8276
    E-ISSN: 1944-8007
    Source: Alma/SFX Local Collection
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  • 2
    Language: English
    In: Journal of geophysical research. Atmospheres, 2014-07-16, Vol.119 (13), p.7889-7907
    Description: The uncertainties in current global and regional climate model integrations are partly related to the representation of clouds, moist convection, and complex topography, thus motivating the use of convection‐resolving models. On climate time scales, convection‐resolving methods have been used for process studies, but application to long‐term scenario simulations has been very limited. Here we present a convection‐resolving simulation for a 10 yearlong period (1998–2007) integrated with the Consortium for Small‐Scale Modeling in Climate Mode model. Two one‐way nested grids are used with horizontal resolutions of 2.2 km for a convection‐resolving model (CRM2) on an extended Alpine domain (1100 km × 1100 km) and 12 km for a convection‐parametrizing model (CPM12) covering Europe. CPM12 is driven by lateral boundary conditions from the ERA‐Interim reanalysis. Validation is conducted against high‐resolution surface data. The CRM2 model strongly improves the simulation of the diurnal cycles of precipitation and temperature, despite an enhanced warm bias and a tendency for the overestimation of precipitation over the Alps. The CPM12 model has a poor diurnal cycle associated with the use of parameterized convection. The assessment of extreme precipitation events reveals that both models adequately represent the frequency‐intensity distributions for daylong events in summer, but large differences occur for hourly precipitation. The CPM12 model underestimates the frequency of heavy hourly events, while CRM2 shows good agreement with observations in the summer season. We also present results on the scaling of precipitation extremes with local daily mean temperatures. In accordance with observations, CRM2 exhibits adiabatic scaling for intermediate hourly events (90th percentile) and superadiabatic scaling for extreme hourly events (99th and 99.9th percentiles) during the summer season. The CPM12 model partly reproduces this scaling as well. The excellent performance of CRM2 in representing hourly precipitation events in terms of intensity and scaling is highly encouraging, as this addresses a previously untested (and untuned) model capability. Key Points Convection‐resolving models improve the simulation of hourly precipitation
    Subject(s): Clausius-Clapeyron ; convection-resolving model ; hourly precipitation ; model evaluation
    ISSN: 2169-897X
    E-ISSN: 2169-8996
    Source: Alma/SFX Local Collection
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  • 3
    Language: English
    In: Nature geoscience, 2016-07-11, Vol.9 (8), p.584-589
    ISSN: 1752-0894
    E-ISSN: 1752-0908
    Source: Nature Journals Online
    Source: ProQuest Central
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  • 4
    Language: English
    In: Journal of geophysical research. Atmospheres, 2017-05-27, Vol.122 (10), p.5237-5258
    Description: Convection‐resolving models allow to explicitly resolve deep convection at horizontal grid spacings of O(1 km). On current supercomputers, refining the grid spacing to the kilometer scale is computationally still extremely demanding, and therefore, climate simulations at this resolution have so far largely been limited to subcontinental computational domains. However, new supercomputers that mix conventional multicore CPUs and accelerators possess properties beneficial for climate codes. Exploiting these capabilities allows expansion of the size of the computational domains to continental scales. Here we present such a convection‐resolving climate simulation, using a version of the COSMO model, capable of exploiting GPU accelerators. The simulation has a grid spacing of 2.2 km, 1536 × 1536 × 60 grid points, covers the period 1999–2008, and is driven by the ERA‐Interim reanalysis. An assessment of the 10‐year‐long simulation is conducted using a wide range of data sets, including several rain gauge networks, energy balance stations, and a remotely sensed lightning data set. Substantial improvements are found for the 2 km simulation in terms of the diurnal cycles of precipitation. This confirms results found in studies using smaller computational domains. However, the continental‐scale simulations also reveal deficiencies such as substantial performance differences between regions with and without strong orographic forcing. Analysis of the statistical distribution of updrafts and downdrafts shows an increase of the amplitude in seasons with convection and a pronounced asymmetry between updrafts and downdrafts. Furthermore, the analysis of lightning data shows that the convection‐resolving simulation is able to reproduce important features of the annual cycle of deep convection in Europe. Key Points Demonstration of convection‐resolving climate simulations on a continental‐scale computational domain Robust improvements in the representation of summer convection
    Subject(s): convection resolving ; diurnal cycle ; graphics processing unit ; lightning ; moist convection ; regional climate model
    ISSN: 2169-897X
    E-ISSN: 2169-8996
    Source: Alma/SFX Local Collection
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  • 5
    Language: English
    In: Reviews of geophysics (1985), 2015-06, Vol.53 (2), p.323-361
    Description: Regional climate modeling using convection‐permitting models (CPMs; horizontal grid spacing 〈4 km) emerges as a promising framework to provide more reliable climate information on regional to local scales compared to traditionally used large‐scale models (LSMs; horizontal grid spacing 〉10 km). CPMs no longer rely on convection parameterization schemes, which had been identified as a major source of errors and uncertainties in LSMs. Moreover, CPMs allow for a more accurate representation of surface and orography fields. The drawback of CPMs is the high demand on computational resources. For this reason, first CPM climate simulations only appeared a decade ago. In this study, we aim to provide a common basis for CPM climate simulations by giving a holistic review of the topic. The most important components in CPMs such as physical parameterizations and dynamical formulations are discussed critically. An overview of weaknesses and an outlook on required future developments is provided. Most importantly, this review presents the consolidated outcome of studies that addressed the added value of CPM climate simulations compared to LSMs. Improvements are evident mostly for climate statistics related to deep convection, mountainous regions, or extreme events. The climate change signals of CPM simulations suggest an increase in flash floods, changes in hail storm characteristics, and reductions in the snowpack over mountains. In conclusion, CPMs are a very promising tool for future climate research. However, coordinated modeling programs are crucially needed to advance parameterizations of unresolved physics and to assess the full potential of CPMs. Key Points Convection‐permitting climate models reduce errors in large‐scale models Added value in convective processes, regional extremes, and over mountains Discusses challenges/potentials of convection‐permitting climate simulations
    Subject(s): added value ; Atmospheric Processes ; climate ; Climate Impact ; Climate Impacts ; Climate Interactions ; cloud resolving ; convection-permitting modeling ; Convective Processes ; ENVIRONMENTAL SCIENCES ; Extreme Events ; Global Change ; high resolution ; Hydrology ; Impacts of Global Change ; Mathematical Geophysics ; Natural Hazards ; nonhydrostatic modeling ; Persistence, Memory, Correlations, Clustering ; Physical Modeling ; Precipitation ; Regional Climate Change ; Regional Modeling ; Review ; Volcano ; Volcanology
    ISSN: 8755-1209
    E-ISSN: 1944-9208
    Source: Wiley Online Library All Journals
    Source: Alma/SFX Local Collection
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  • 6
    Language: English
    In: Climate dynamics, 2020-07, Vol.55 (1-2), p.35-59
    Subject(s): Analysis ; Climate
    ISSN: 0930-7575
    E-ISSN: 1432-0894
    Source: Academic Search Ultimate
    Source: Alma/SFX Local Collection
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  • 7
    Language: English
    In: Journal of climate, 2020-03-01, Vol.33 (5), p.1915-1933
    Description: AbstractThe “gray zone” of convection is defined as the range of horizontal grid-space resolutions at which convective processes are partially but not fully resolved explicitly by the model dynamics (typically estimated from a few kilometers to a few hundred meters). The representation of convection at these scales is challenging, as both parameterizing convective processes or relying on the model dynamics to resolve them might cause systematic model biases. Here, a regional climate model over a large European domain is used to study model biases when either using parameterizations of deep and shallow convection or representing convection explicitly. For this purpose, year-long simulations at horizontal resolutions between 50- and 2.2-km grid spacing are performed and evaluated with datasets of precipitation, surface temperature, and top-of-the-atmosphere radiation over Europe. While simulations with parameterized convection seem more favorable than using explicit convection at around 50-km resolution, at higher resolutions (grid spacing ≤ 25 km) models tend to perform similarly or even better for certain model skills when deep convection is turned off. At these finer scales, the representation of deep convection has a larger effect in model performance than changes in resolution when looking at hourly precipitation statistics and the representation of the diurnal cycle, especially over nonorographic regions. The shortwave net radiative balance at the top of the atmosphere is the variable most strongly affected by resolution changes, due to the better representation of cloud dynamical processes at higher resolutions. These results suggest that an explicit representation of convection may be beneficial in representing some aspects of climate over Europe at much coarser resolutions than previously thought, thereby reducing some of the uncertainties derived from parameterizing deep convection.
    ISSN: 0894-8755
    E-ISSN: 1520-0442
    Source: Academic Search Ultimate
    Source: Alma/SFX Local Collection
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  • 8
    Language: English
    In: Climate dynamics, 2020-07, Vol.55 (1-2), p.61-75
    Subject(s): Air pollution ; Analysis ; Climate models ; Global temperature changes ; Greenhouse gases ; Models ; Precipitation (Meteorology)
    ISSN: 0930-7575
    E-ISSN: 1432-0894
    Source: Academic Search Ultimate
    Source: Alma/SFX Local Collection
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  • 9
    Language: English
    In: Climatic change, 2016-07, Vol.137 (1), p.201-216
    Description: Many climate studies assess trends and projections in heavy precipitation events using precipitation percentile (or quantile) indices. Here we investigate three different percentile indices that are commonly used. We demonstrate that these may produce very different results and thus require great care with interpretation. More specifically, consideration is given to two intensity-based indices and one frequency-based index, namely (a) all-day percentiles, (b) wet-day percentiles, and (c) frequency indices based on the exceedance of a percentile threshold.Wet-day percentiles are conditionally computed for the subset of wet events (with precipitation exceeding some threshold, e.g. 1 mm/d for daily precipitation). We present evidence that this commonly used methodology can lead to artifacts and misleading results if significant changes in the wet-day frequency are not accounted for. Percentile threshold indices measure the frequency of exceedance with respect to a percentile-based threshold. We show that these indices yield an assessment of changes in heavy precipitation events that is qualitatively consistent with all-day percentiles, but there are substantial differences in quantitative terms. We discuss the reasons for these effects, present a theoretical assessment, and provide a series of examples using global and regional climate models to quantify the effects in typical applications.Application to climate model output shows that these considerations are relevant to a wide range of typical climate-change applications. In particular, wet-day percentiles generally yield different results, and in most instances should not be used for the impact-oriented assessment of changes in heavy precipitation events.
    Subject(s): Atmospheric Sciences ; Climate Change/Climate Change Impacts ; Climatic changes ; Earth Sciences ; Environment ; Precipitation variability ; Research
    ISSN: 0165-0009
    E-ISSN: 1573-1480
    Source: Alma/SFX Local Collection
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  • 10
    Language: English
    In: Climate dynamics, 2018-06, Vol.50 (11), p.4455-4480
    Description: Over the past few decades the horizontal resolution of regional climate models (RCMs) has steadily increased, leading to a better representation of small-scale topographic features and more details in simulating dynamical aspects, especially in coastal regions and over complex terrain. Due to its complex terrain, the broader Adriatic region represents a major challenge to state-of-the-art RCMs in simulating local wind systems realistically. The objective of this study is to identify the added value in near-surface wind due to the refined grid spacing of RCMs. For this purpose, we use a multi-model ensemble composed of CORDEX regional climate simulations at 0.11° and 0.44° grid spacing, forced by the ERA-Interim reanalysis, a COSMO convection-parameterizing simulation at 0.11° and a COSMO convection-resolving simulation at 0.02° grid spacing. Surface station observations from this region and satellite QuikSCAT data over the Adriatic Sea have been compared against daily output obtained from the available simulations. Both day-to-day wind and its frequency distribution are examined. The results indicate that the 0.44° RCMs rarely outperform ERA-Interim reanalysis, while the performance of the high-resolution simulations surpasses that of ERA-Interim. We also disclose that refining the grid spacing to a few km is needed to properly capture the small-scale wind systems. Finally, we show that the simulations frequently yield the accurate angle of local wind regimes, such as for the Bora flow, but overestimate the associated wind magnitude. Finally, spectral analysis shows good agreement between measurements and simulations, indicating the correct temporal variability of the wind speed.
    Subject(s): Adriatic region ; Atmospheric circulation ; Climate models ; Climatology ; Convection-resolving models ; CORDEX ; Earth Sciences ; Geophysics/Geodesy ; Models ; Oceanography ; Regional climate models ; Usage
    ISSN: 0930-7575
    E-ISSN: 1432-0894
    Source: Academic Search Ultimate
    Source: Alma/SFX Local Collection
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