AGW Observer

Observations of anthropogenic global warming

New research – atmospheric and oceanic circulation (August 10, 2016)

Posted by Ari Jokimäki on August 10, 2016

Some of the latest papers on atmospheric and oceanic circulation are shown below. First a few highlighted papers with abstracts and then a list of some other papers. If this subject interests you, be sure to check also the other papers – they are by no means less interesting than the highlighted ones.

Highlights

The North Atlantic Oscillation as a driver of rapid climate change in the Northern Hemisphere (Delworth et al. 2016) http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2738.html

Abstract: Pronounced climate changes have occurred since the 1970s, including rapid loss of Arctic sea ice, large-scale warming and increased tropical storm activity in the Atlantic. Anthropogenic radiative forcing is likely to have played a major role in these changes, but the relative influence of anthropogenic forcing and natural variability is not well established. The above changes have also occurred during a period in which the North Atlantic Oscillation has shown marked multidecadal variations. Here we investigate the role of the North Atlantic Oscillation in these rapid changes through its influence on the Atlantic meridional overturning circulation and ocean heat transport. We use climate models to show that observed multidecadal variations of the North Atlantic Oscillation can induce multidecadal variations in the Atlantic meridional overturning circulation and poleward ocean heat transport in the Atlantic, extending to the Arctic. Our results suggest that these variations have contributed to the rapid loss of Arctic sea ice, Northern Hemisphere warming, and changing Atlantic tropical storm activity, especially in the late 1990s and early 2000s. These multidecadal variations are superimposed on long-term anthropogenic forcing trends that are the dominant factor in long-term Arctic sea ice loss and hemispheric warming.

Evidence of global warming impact on the evolution of the Hadley Circulation in ECMWF centennial reanalyses (D’Agostino & Lionello, 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3250-0

Abstract: This study analyzes the evolution of the Hadley Circulation (HC) during the twentieth century in ERA-20CM (AMIP-experiment) and ERA-20C (reanalysis). These two recent ECMWF products provide the opportunity for a new analysis of the HC trends and of their uncertainties. Further, the effect of sea surface temperature forcing (including its uncertainty) and data assimilation are investigated. Also the ECMWF reanalysis ERA-Interim, for the period 1979–2010, is considered for a complementary analysis. Datasets present important differences in characteristics and trends of the HC. In ERA-20C HC is weaker (especially the Southern Hemisphere HC) and the whole Northern Hemisphere HC is located more southward than in ERA-20CM (especially in the boreal summer). In ERA-Interim HC is stronger and wider than both other simulations. In general, the magnitude of trends is larger and more statistically significant in ERA-20C than in ERA-20CM. The presence of large multidecadal variability across twentieth century raises doubts on the interpretation of recent behavior, such as the onset of sustained long term trends, particularly for the HC strength. In spite of this, the southward shift of the Southern Edge and widening of the Southern Hemisphere HC appear robust features in all datasets, and their trends have accelerated in the last three decades, but actual expansion rates remain affected by considerable uncertainty. Inconsistencies between datasets are attributed to the different reproduction of the links between the HC width and factors affecting it (such as mean global temperature, tropopause height, meridional temperature contrast and planetary waves), which appear more robust in ERA-20CM than in ERA-20C, particularly for the two latter factors. Further, in ERA-Interim these correlations are not statistically significant. These outcomes suggest that data assimilation degrades the links between the HC and features influencing its dynamics.

Impact of slowdown of Atlantic overturning circulation on heat and freshwater transports (Kelly et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069789/abstract

Abstract: Recent measurements of the strength of the Atlantic overturning circulation at 26°N show a 1 year drop and partial recovery amid a gradual weakening. To examine the extent and impact of the slowdown on basin wide heat and freshwater transports for 2004–2012, a box model that assimilates hydrographic and satellite observations is used to estimate heat transport and freshwater convergence as residuals of the heat and freshwater budgets. Using an independent transport estimate, convergences are converted to transports, which show a high level of spatial coherence. The similarity between Atlantic heat transport and the Agulhas Leakage suggests that it is the source of the surface heat transport anomalies. The freshwater budget in the North Atlantic is dominated by a decrease in freshwater flux. The increasing salinity during the slowdown supports modeling studies that show that heat, not freshwater, drives trends in the overturning circulation in a warming climate.

The response of high-impact blocking weather systems to climate change (Kennedy et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069725/abstract

Abstract: Midlatitude weather and climate are dominated by the jet streams and associated eastward moving storm systems. Occasionally, however, these are blocked by persistent anticyclonic regimes known as blocking. Climate models generally predict a small decline in blocking frequency under anthropogenic climate change. However, confidence in these predictions is undermined by, among other things, a lack of understanding of the physical mechanisms underlying the change. Here we analyze blocking (mostly in the Euro-Atlantic sector) in a set of sensitivity experiments to determine the effect of different parts of the surface global warming pattern. We also analyze projected changes in the impacts of blocking such as temperature extremes. The results show that enhanced warming both in the tropics and over the Arctic act to strengthen the projected decline in blocking. The tropical changes are more important for the uncertainty in projected blocking changes, though the Arctic also affects the temperature anomalies during blocking.

The anomalous change in the QBO in 2015-16 (Newman et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070373/abstract

Abstract: The quasi-biennial oscillation (QBO) is a tropical lower stratospheric, downward propagating zonal wind variation, with an average period of ~28 months. The QBO has been constantly documented since 1953. Here we describe the evolution of the QBO during the Northern Hemisphere winter of 2015-16 using radiosonde observations and meteorological reanalyses. Normally, the QBO would show a steady downward propagation of the westerly phase. In 2015-16, there was an anomalous upward displacement of this westerly phase from ~30 hPa to 15 hPa. These westerlies impinge on, or “cut-off” the normal downward propagation of the easterly phase. In addition, easterly winds develop at 40 hPa. Comparisons to tropical wind statistics for the 1953-present record demonstrate that this 2015-16 QBO disruption is unprecedented.

Other papers

Impact of observed North Atlantic multidecadal variations to European summer climate: a linear baroclinic response to surface heating (Ghosh et al. 2016) http://rd.springer.com/article/10.1007%2Fs00382-016-3283-4

Gridded, monthly rainfall and temperature climatology for El Niño Southern Oscillation impacts in the United States (Dourte et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4820/abstract

Southern European rainfall reshapes the early-summer circumglobal teleconnection after the late 1970s (Lin et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3306-1

Moisture and heat budgets of the south American monsoon system: climatological aspects (Garcia et al. 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1882-y

The Relative Influence of ENSO and SAM on Antarctic Peninsula Climate (Clem et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025305/abstract

Sinuosity of mid-latitude atmospheric flow in a warming world (Cattiaux et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070309/abstract

ENSO response to high-latitude volcanic eruptions in the Northern Hemisphere: The role of the initial conditions (Pausata et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069575/abstract

Remote influence of Interdecadal Pacific Oscillation on the South Atlantic Meridional Overturning Circulation variability (Lopez et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069067/abstract

Robust response of the Amundsen Sea Low to stratospheric ozone depletion (England et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070055/abstract

The response of winter Pacific North American pattern to strong volcanic eruptions (Liu et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3287-0

Atlantic Multidecadal Variability in a model with an improved North Atlantic Current (Drews & Greatbatch, 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069815/abstract

Sub-decadal North Atlantic Oscillation variability in observations and the Kiel Climate Model (Reintges, Latif & Park, 2016) http://rd.springer.com/article/10.1007%2Fs00382-016-3279-0

Is there a robust effect of anthropogenic aerosols on the Southern Annular Mode? (Steptoe et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2015JD024218/abstract

Climate Signals in the Mid- to High-Latitude North Atlantic from Altimeter Observations (Li et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00670.1

Intensification and poleward shift of subtropical western boundary currents in a warming climate (Yang et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2015JC011513/abstract

Inter-basin effects of the Indian Ocean on Pacific decadal climate change (Mochizuki et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069940/abstract

The influence of boreal spring Arctic Oscillation on the subsequent winter ENSO in CMIP5 models (Chen et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3243-z

Relationship between North American winter temperature and large-scale atmospheric circulation anomalies and its decadal variation (Yu et al. 2016) http://iopscience.iop.org/article/10.1088/1748-9326/11/7/074001/meta

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