scholarly journals Assessing the impact of SSTs on a simulated medicane using ensemble simulations

2018 ◽  
Author(s):  
Robin Noyelle ◽  
Uwe Ulbrich ◽  
Nico Becker ◽  
Edmund P. Meredith
Keyword(s):  
Climate Model ◽  
Regional Climate ◽  
Western Mediterranean ◽  
Tyrrhenian Sea ◽  
Western Mediterranean Basin ◽  
Minor Influence ◽  
Climate Model Simulations ◽  
Upper Level ◽  
A Minor ◽  
The Impact

Abstract. The sensitivity of the October 1996 medicane in the western Mediterranean basin to sea surface temperatures (SSTs) is investigated via 24-member ensembles of regional climate model simulations. Eleven ensembles are created by uniformly changing SSTs in a range of −4 K to +6 K from the observed field, with a 1 K step. By using a modified phase space diagram and a simple compositing method, it is shown that the SST state has a minor influence on the tracks of the cyclones, but a strong influence on their intensities. Increased SSTs lead to greater probabilities of tropical transitions, to stronger low- and upper-level warm cores, and to lower pressure minima. The tropical transition occurs sooner and lasts longer, which enables a greater number of transitioning cyclones to survive landfall over Sardinia and to re-intensify in the Tyrrhenian Sea. The results demonstrate that SSTs influence the intensity of fluxes from the sea, which leads to greater convective activity before the storms reach their maturity. These results suggest that the processes at steady-state for medicanes are very similar to tropical cyclones.

scholarly journals Assessing the impact of sea surface temperatures on a simulated medicane using ensemble simulations

2019 ◽  
Vol 19 (4) ◽  
pp. 941-955 ◽  
Author(s):  
Robin Noyelle ◽  
Uwe Ulbrich ◽  
Nico Becker ◽  
Edmund P. Meredith
Keyword(s):  
Climate Model ◽  
Regional Climate ◽  
Western Mediterranean ◽  
Sea Surface ◽  
Tyrrhenian Sea ◽  
Sea Surface Temperatures ◽  
Surface Temperatures ◽  
Western Mediterranean Basin ◽  
A Minor ◽  
The Impact

Abstract. The sensitivity of the October 1996 Medicane in the western Mediterranean basin to sea surface temperatures (SSTs) is investigated with a regional climate model via ensemble sensitivity simulations. For 11 SST states, ranging from −4 K below to +6 K above the observed SST field (in 1 K steps), 24-member ensembles of the medicane are simulated. By using a modified phase space diagram and a simple compositing method, it is shown that the SST state has a minor influence on the tracks of the cyclones but a strong influence on their intensities. Increased SSTs lead to greater probabilities of tropical transitions, to stronger lower- and upper-level warm cores and to lower pressure minima. The tropical transition occurs sooner and lasts longer, which enables a greater number of transitioning cyclones to survive landfall over Sardinia and re-intensify in the Tyrrhenian Sea. The results demonstrate that SSTs influence the intensity of fluxes from the sea, which leads to greater convective activity before the storms reach their maturity. These results suggest that the processes at steady state for medicanes are very similar to tropical cyclones.

scholarly journals Model and Observational Analysis of the Northeast U.S. Regional Climate and Its Relationship to the PNA and NAO Patterns during Early Winter

2006 ◽  
Vol 134 (11) ◽  
pp. 3479-3505 ◽  
Author(s):  
M. Notaro ◽  
W-C. Wang ◽  
W. Gong
Keyword(s):  
New York ◽  
Great Lakes ◽  
Large Scale ◽  
Climate Model ◽  
Regional Climate ◽  
Early Winter ◽  
Upper Level ◽  
Upper Level Jet ◽  
The Impact ◽  
Nao Pattern

Abstract The relationship between the large-scale circulation and regional climate of the northeast United States is investigated for early winter using observational data and the State University of New York at Albany regional climate model. Simulated patterns of temperature, precipitation, and atmospheric circulation compare well with observations, despite a cold, dry bias. Ten December runs are analyzed to investigate the impact of the Pacific–North American (PNA) pattern on temperature, precipitation, clouds, and circulation features. During a positive PNA pattern, the simulated and observed eastern U.S. jet shifts to the southeast, coinciding with cold, dry conditions in the Northeast. This shift and intensification of the upper-level jet stream during a positive PNA pattern coincides with a greater frequency of cyclones and anticyclones along a distinct southwest–northeast track. Despite increased cyclone activity, total wintertime precipitation is below normal during a positive PNA pattern because of enhanced stability and subsidence over land, along with lower-atmospheric moisture content. Lower surface air temperatures during a positive PNA pattern result in enhanced simulated cloud cover over the Great Lakes and Atlantic Ocean due to increased thermal contrast and fluxes of sensible and latent heat, and a reduction in clouds over land. Interactions between the PNA and North Atlantic Oscillation (NAO) patterns impact the Northeast winter climate. Observed frontal passages through New York are most abundant during a negative PNA and positive NAO pattern, with a zonal upper-level jet positioned over New York. A positive PNA pattern is frequently characterized by an earlier observed Great Lakes ice season, while the greatest lake-effect snowfall occurs during a positive PNA and negative NAO pattern. The NAO pattern has the largest impact on northeast U.S. temperatures and the eastern U.S. upper-level jet during a positive PNA pattern.

scholarly journals Secondary Cyclogenesis along an Occluded Front Leading to Damaging Wind Gusts: Windstorm Kyrill, January 2007

2015 ◽  
Vol 143 (4) ◽  
pp. 1417-1437 ◽  
Author(s):  
Patrick Ludwig ◽  
Joaquim G. Pinto ◽  
Simona A. Hoepp ◽  
Andreas H. Fink ◽  
Suzanne L. Gray
Keyword(s):  
Climate Model ◽  
Regional Climate ◽  
Surface Wind ◽  
Lower Troposphere ◽  
Spatiotemporal Resolution ◽  
Wind Gusts ◽  
Sensitivity Studies ◽  
Climate Model Simulations ◽  
Upper Level ◽  
Upper Level Jet

Abstract Windstorm Kyrill affected large parts of Europe in January 2007 and caused widespread havoc and loss of life. In this study the formation of a secondary cyclone, Kyrill II, along the occluded front of the mature cyclone Kyrill and the occurrence of severe wind gusts as Kyrill II passed over Germany are investigated with the help of high-resolution regional climate model simulations. Kyrill underwent an explosive cyclogenesis south of Greenland as the storm crossed poleward of an intense upper-level jet stream. Later in its life cycle secondary cyclogenesis occurred just west of the British Isles. The formation of Kyrill II along the occluded front was associated (i) with frontolytic strain and (ii) with strong diabatic heating in combination with a developing upper-level shortwave trough. Sensitivity studies with reduced latent heat release feature a similar development but a weaker secondary cyclone, revealing the importance of diabatic processes during the formation of Kyrill II. Kyrill II moved farther toward Europe and its development was favored by a split jet structure aloft, which maintained the cyclone’s exceptionally deep core pressure (below 965 hPa) for at least 36 h. The occurrence of hurricane-force winds related to the strong cold front over north and central Germany is analyzed using convection-permitting simulations. The lower troposphere exhibits conditional instability, a turbulent flow, and evaporative cooling. Simulation at high spatiotemporal resolution suggests that the downward mixing of high momentum (the wind speed at 875 hPa widely exceeded 45 m s−1) accounts for widespread severe surface wind gusts, which is in agreement with observed widespread losses.

scholarly journals New Tree-Ring Evidence from the Pyrenees Reveals Western Mediterranean Climate Variability since Medieval Times

2017 ◽  
Vol 30 (14) ◽  
pp. 5295-5318 ◽  
Author(s):  
Ulf Büntgen ◽  
Paul J. Krusic ◽  
Anne Verstege ◽  
Gabriel Sangüesa-Barreda ◽  
Sebastian Wagner ◽  
...  
Keyword(s):  
Climate Variability ◽  
Climate Model ◽  
Regional Climate ◽  
Volcanic Eruptions ◽  
High Elevation ◽  
Western Mediterranean ◽  
European Alps ◽  
Model Simulations ◽  
Latewood Density ◽  
Western Mediterranean Basin

Paleoclimatic evidence is necessary to place the current warming and drying of the western Mediterranean basin in a long-term perspective of natural climate variability. Annually resolved and absolutely dated temperature proxies south of the European Alps that extend back into medieval times are, however, mainly limited to measurements of maximum latewood density (MXD) from high-elevation conifers. Here, the authors present the world’s best replicated MXD site chronology of 414 living and relict Pinus uncinata trees found >2200 m above mean sea level (MSL) in the Spanish central Pyrenees. This composite record correlates significantly ( p ≤ 0.01) with May–June and August–September mean temperatures over most of the Iberian Peninsula and northern Africa ( r = 0.72; 1950–2014). Spanning the period 1186–2014 of the Common Era (CE), the new reconstruction reveals overall warmer conditions around 1200 and 1400, and again after around 1850. The coldest reconstructed summer in 1258 (−4.4°C compared to 1961–90) followed the largest known volcanic eruption of the CE. The twentieth century is characterized by pronounced summer cooling in the 1970s, subsequently rising temperatures until 2003, and a slowdown of warming afterward. Little agreement is found with climate model simulations that consistently overestimate recent summer warming and underestimate preindustrial temperature changes. Interannual–multidecadal covariability with regional hydroclimate includes summer pluvials after large volcanic eruptions. This study demonstrates the relevance of updating MXD-based temperature reconstructions, not only back in time but also toward the present, and emphasizes the importance of comparing temperature and hydroclimatic proxies, as well as model simulations for understanding regional climate dynamics.

Drought assessment in a changing climate with the joint deficit index

2020 ◽  
Author(s):  
Hans Van de Vyver ◽  
Joris Van den Bergh ◽  
Bert Van Schaeybroeck
Keyword(s):  
Climate Model ◽  
Regional Climate ◽  
Gaussian Copula ◽  
Drought Assessment ◽  
Covariance Models ◽  
Climate Model Simulations ◽  
Joint Deficit Index ◽  
The Impact

<p>The characterization of droughts is very dependent on the time scale that is involved. To obtain an overall drought assessment, the cumulative effects of water deficits over different times need to be examined together. For instance, the joint deficit index (JDI) is based on multivariate probabilities of precipitation over various time scales from 1- to 12-months, and was constructed from empirical copulas. We examine the Gaussian copula model for the JDI, and we model the covariance across the temporal scales with a two-parameter function that is commonly used in the specific context of spatial statistics or geostatistics. The validity of the covariance models is demonstrated with long-term precipitation series.</p><p>Next, we assess the impact of climate change on future droughts, based on the JDI. We select an ensemble of CORDEX regional climate model simulations, under the emission pathways RCP4.5 and RCP8.5. The CORDEX resolution used is 0.11 degree (EUR-11). In particular, distributional changes in the JDI are analysed for the Brussels-Capital Region. This area contains climatological and synoptic stations that are operated by the Royal Meteorological Institute of Belgium, with long-term series.</p><p> </p>

scholarly journals Where Does the Irrigation Water Go? An Estimate of the Contribution of Irrigation to Precipitation Using MERRA

2013 ◽  
Vol 14 (1) ◽  
pp. 275-289 ◽  
Author(s):  
Jiangfeng Wei ◽  
Paul A. Dirmeyer ◽  
Dominik Wisser ◽  
Michael G. Bosilovich ◽  
David M. Mocko
Keyword(s):  
Hydrological Model ◽  
Climate Model ◽  
Regional Climate ◽  
Back Trajectory ◽  
Percentage Increase ◽  
Weather Forecasts ◽  
Explicit Consideration ◽  
Precipitation Increase ◽  
Climate Model Simulations ◽  
The Impact

Abstract Irrigation is an important human activity that may impact local and regional climate, but current climate model simulations and data assimilation systems generally do not explicitly include it. The European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim) shows more irrigation signal in surface evapotranspiration (ET) than the Modern-Era Retrospective Analysis for Research and Applications (MERRA) because ERA-Interim adjusts soil moisture according to the observed surface temperature and humidity while MERRA has no explicit consideration of irrigation at the surface. But, when compared with the results from a hydrological model with detailed considerations of agriculture, the ET from both reanalyses show large deficiencies in capturing the impact of irrigation. Here, a back-trajectory method is used to estimate the contribution of irrigation to precipitation over local and surrounding regions, using MERRA with observation-based corrections and added irrigation-caused ET increase from the hydrological model. Results show substantial contributions of irrigation to precipitation over heavily irrigated regions in Asia, but the precipitation increase is much less than the ET increase over most areas, indicating that irrigation could lead to water deficits over these regions. For the same increase in ET, precipitation increases are larger over wetter areas where convection is more easily triggered, but the percentage increase in precipitation is similar for different areas. There are substantial regional differences in the patterns of irrigation impact, but, for all the studied regions, the highest percentage contribution to precipitation is over local land.

scholarly journals Explicit Convection and Scale-Aware Cumulus Parameterizations: High-Resolution Simulations over Areas of Different Topography in Germany

2018 ◽  
Vol 146 (6) ◽  
pp. 1925-1944 ◽  
Author(s):  
Andreas Wagner ◽  
Dominikus Heinzeller ◽  
Sven Wagner ◽  
Thomas Rummler ◽  
Harald Kunstmann
Keyword(s):  
High Resolution ◽  
Land Surface ◽  
Climate Model ◽  
Regional Climate ◽  
Surface Characteristics ◽  
Radar Data ◽  
Explicit Calculation ◽  
Climate Model Simulations ◽  
Convection Parameterization ◽  
The Impact

An increase in the spatial resolution of regional climate model simulations improves the representation of land surface characteristics and may allow the explicit calculation of important physical processes such as convection. The present study investigates further potential benefits with respect to precipitation, based on a small ensemble of high-resolution simulations with WRF with grid spacings up to 1 km. The skill of each experiment is evaluated regarding the temporal and spatial performance of the simulation of precipitation of one year over both a mountainous region in southwestern Germany and a mainly flat region in northern Germany. This study allows us to differentiate between the impact of grid spacing, topography, and convection parameterization. Furthermore, the performance of a state-of-the-art convection parameterization scheme in the gray zone of convection is evaluated against an explicit calculation of convection only. Our evaluation demonstrates the following: high-resolution simulations (5 and 1 km) are generally able to represent the diurnal cycle, structure, and intensity distribution of precipitation, when compared to observational datasets such as radar data and interpolated station data. The influence of the improved representation of the topography at higher resolution (1 km) becomes apparent in complex terrain, where the localization of precipitation maxima is more accurate, although these maxima are overestimated. In flat areas, differences in spatial evaluations arise between simulations with parameterized and explicitly calculated convection, whereas smaller grid spacings (1 km vs 5 km) show hardly any impact on precipitation results.

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