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CreativeCommons  attribution  Tolkien  from twitter
9 days ago by tolkien
Global and Regional Increase of Precipitation Extremes under Global Warming - Papalexiou - - Water Resources Research - Wiley Online Library
Papalexiou et al 2019: Global warming is expected to change the regime of extreme precipitation. Physical laws translate increasing atmospheric heat into increasing atmospheric water content that drives precipitation changes. Within the literature, general agreement is that extreme precipitation is changing, yet different assessment methods, datasets, and study periods, may result in different patterns and rates of change. Here we perform a global analysis of 8730 daily precipitation records focusing on the 1964‐2013 period when the global warming accelerates. We introduce a novel analysis of the N largest extremes in records having N complete years within the study period. Based on these extremes, which represent more accurately heavy precipitation than annual maxima, we form time series of their annual frequency and mean annual magnitude. The analysis offers new insights and reveals: (1) global and zonal increasing trends in the frequency of extremes that are highly unlikely under the assumption of stationarity, and (2) magnitude changes that are not as evident. Frequency changes reveal a coherent spatial pattern with increasing trends being detected in large parts of Eurasia, North Australia, and the Midwestern United States. Globally, over the last decade of the studied period we find 7% more extreme events than the expected number. Finally, we report that changes in magnitude are not in general correlated with changes in frequency.
Climate_Science_study  extremePrecipitation  detection  attribution  MidWest 
11 days ago by huntercutting
Japan’s deadly heatwave would have been impossible without climate change — Quartz
Japan’s heatwave in July 2018 could not have happened without climate change.

That is the unequivocal conclusion of a report released last week, as the country battles yet another record-breaking heatwave.

The July 2018 heatwave, which killed 1,032 people, saw temperatures reach 41.1C (106F), the highest temperature ever recorded in the country. Torrential rains also triggered landslides and the worst flooding in decades.

Penned by the Meteorological Society of Japan, the study is the first to establish that some aspects of the international heatwave could not have occurred in the absence of global warming. Scientists reached this conclusion by employing a technique known as event attribution (EA).
Japan  Climate_Science_study  attribution  heatwaves 
15 days ago by huntercutting
Human Influence on Winter Precipitation Trends (1921–2015) over North America and Eurasia Revealed by Dynamical Adjustment - Guo - 2019 - Geophysical Research Letters - Wiley Online Library
Guoa et al. 2019: Detecting and attributing a human influence on observed rainfall trends is a major challenge due to the presence of large amplitude internal variability on all time scales and by limited temporal and spatial data coverage. Here we apply a “dynamical adjustment” methodology to a gridded archive of monthly precipitation to estimate an anthropogenic influence on long‐term (1920–2015) trends over North America and Eurasia during winter (November–March). This empirical approach aims to remove atmospheric circulation influences from precipitation variability and trends, thereby revealing the thermodynamically induced component as a residual. The geographical pattern and amplitude of this observed thermodynamic residual precipitation trend are in good agreement with anthropogenically forced trends obtained from ensembles of historical climate model simulations. Such consistency helps to reconcile observations and models and provides compelling evidence for a human influence on century‐scale precipitation trends over North America and Eurasia during the cold season.
Plain Language Summary

It is difficult to isolate the anthropogenic influence on long‐term precipitation trends due to confounding effects from internal variability. Here we remove the influence of atmospheric circulation variability, which is primarily unforced, from observed precipitation trends using an empirical approach called “dynamical adjustment.” This removal isolates the thermodynamic component of observed precipitation trends as a residual. We find that this thermodynamic component is in good agreement with the anthropogenic component determined from historical simulations from climate models. Thus, we conclude that we are able to identify a human influence on observed century‐scale precipitation trends over North America and Eurasia.
USA  precipitation  attribution  detection  Climate_Science_study 
18 days ago by huntercutting
A warming Arctic produces weather extremes in our latitudes -- ScienceDaily
Science Daily on Romanowski et al 2019: Atmospheric researchers at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) have now developed a climate model that can accurately depict the frequently observed winding course of the jet stream, a major air current over the Northern Hemisphere. The breakthrough came when the scientists combined their global climate model with a new machine learning algorithm on ozone chemistry. Using their new combo-model, they can now show that the jet stream's wavelike course in winter and subsequent extreme weather conditions cold air outbreaks in Central Europe and North America are the direct result of climate change. Their findings were released in the Nature online portal Scientific Reports on 28 May 2019.

"Our study shows that the changes in the jet stream are at least partly due to the loss of Arctic sea ice. If the ice cover continues to dwindle, we believe that both the frequency and intensity of the extreme weather events previously observed in the middle latitudes will increase," says Prof Markus Rex, Head of Atmospheric Research at the AWI. "In addition, our findings confirm that the more frequently occurring cold phases in winter in the USA, Europe and Asia are by no means a contradiction to global warming; rather, they are a part of anthropogenic climate change."
Climate_Science_study  circulationchanges  jetstream  Arctic_sea_ice  ArcticAmplifcation  warm-arctic-cold-continents  polarvortex  detection  attribution 
18 days ago by huntercutting
The role of stratospheric ozone for Arctic-midlatitude linkages | Scientific Reports
Romanowsky et al 2019: Arctic warming was more pronounced than warming in midlatitudes in the last decades making this region a hotspot of climate change. Associated with this, a rapid decline of sea-ice extent and a decrease of its thickness has been observed. Sea-ice retreat allows for an increased transport of heat and momentum from the ocean up to the tropo- and stratosphere by enhanced upward propagation of planetary-scale atmospheric waves. In the upper atmosphere, these waves deposit the momentum transported, disturbing the stratospheric polar vortex, which can lead to a breakdown of this circulation with the potential to also significantly impact the troposphere in mid- to late-winter and early spring. Therefore, an accurate representation of stratospheric processes in climate models is necessary to improve the understanding of the impact of retreating sea ice on the atmospheric circulation.

During low-ice conditions (LICE) conditions ERA-Interim reanalysis data shows enhanced upward wave propagation from the troposphere into the stratosphere that causes a disturbance of the stratospheric polar vortex, which leads to downward propagating signals in the dynamical atmospheric variables. This process influences tropospheric circulation patterns like the NAO, impacting the daily weather patterns of the midlatitudes. This mechanism can not be fully reproduced by the AGCM ECHAM6, which does not respond with a negative phase shift of the NAO during LICE conditions. Coupling ECHAM6 to the fast but accurate interactive ozone chemistry scheme SWIFT improves the interaction between stratospheric chemistry and dynamics due to a more realistic representation of stratospheric processes. These improvements in the stratosphere also lead to a change in tropospheric teleconnection patterns resulting in a negative NAO response that is comparable to changes seen in reanalysis data.

Our results imply that interactive stratospheric ozone chemistry in winter and spring is important to understand changes in tropospheric teleconnection patterns caused by decreasing Arctic sea ice via the stratospheric pathway. Being computationally feasible, we also suggest the implementation of the fast ozone chemistry scheme SWIFT into other AGCMs enabling very large ensemble sizes compared to classic Chemistry Climate Models.
circulationchanges  Arctic_sea_ice  ArcticAmplifcation  extremeweather  polarvortex  Climate_Science_study  attribution  detection 
18 days ago by huntercutting
To understand customers, first you need to understand their Device Graphs - MarTech Today
Martech Today explainer article on Device Graphs. Mentions vendors Drawbridge and Tapad. Explains significance for attribution
device  graph  ID  explainer  DIG30003  DIG70002  attribution 
19 days ago by pciszewski

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