Structure of the Western Tibetan Vortex inconsistent with a thermally-direct circulation

The Western Tibetan Vortex (WTV) is a large-scale circulation pattern identified from year-to-year circulation variability, which was used to understand the causal mechanisms for slowdown of the glacier melting over the western Tibetan Plateau (TP). A recent argument has suggested the WTV is the set of wind field anomalies resulting from variability in near-surface air temperatures over the western TP (above 1500 m), which, in turn, is likely driven by the surface net radiation. This study thereby evaluates the above putative thermal-direct mechanism. By conducting numerical sensitivity experiments using a global atmospheric circulation model, SAMIL, we find a WTV-like structure cannot be generated from a surface thermal forcing imposed on the western TP. A thermally-direct circulation generated by the surface or near surface heating is expect to cause upward motions and a baroclinic structure above it. In contrast, downward motions and a quasi-barotropic are observed in the vertical structure of the WTV. Besides, we find variability of the surface net radiation (sum of the surface shortwave and longwave net radiation) over the western TP can be traced back to the WTV variability based on ERA5 data. The anticyclonic (cyclonic) WTV reduces (increases) the cloudiness through the anomalous downward (upward) motions, causes more (less) input shortwave net radiation and thereby more (less) surface net radiations, resulting in the warmer (cooler) surface and near-surface air temperature over the western TP. The argument is constructive in encouraging examination of the radiative balance processes that complements previous studies.

Impact of Solar Activity on Global Atmospheric Circulation Based on SD-WACCM-X Simulations from 2002 to 2019

In this study, a global atmospheric model, Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (SD-WACCM-X), and the residual circulation principle were used to study the global atmospheric circulation from the lower to upper atmosphere (~500 km) from 2002 to 2019. Our analysis shows that the atmospheric circulation is clearly influenced by solar activity, especially in the upper atmosphere, which is mainly characterized by an enhanced atmospheric circulation in years with high solar activity. The atmospheric circulation in the upper atmosphere also exhibits an ~11 year period, and its variation is highly correlated with the temporal variation in the F10.7 solar index during the same time series, with a maximum correlation coefficient of up to more than 0.9. In the middle and lower atmosphere, the impact of solar activity on the atmospheric circulation is not as obvious as in the upper atmosphere due to some atmospheric activities such as the Quasi-Biennial Oscillation (QBO), El Niño–Southern Oscillation (ENSO), sudden stratospheric warming (SSW), volcanic forcing, and so on. By comparing the atmospheric circulation in different latitudinal regions between years with high and low solar activity, we found the atmospheric circulation in mid- and high-latitude regions is more affected by solar activity than in low-latitude and equatorial regions. In addition, clear seasonal variation in atmospheric circulation was detected in the global atmosphere, excluding the regions near 10−4 hPa and the lower atmosphere, which is mainly characterized by a flow from the summer hemisphere to the winter hemisphere. In the middle and low atmosphere, the atmospheric circulation shows a quasi-biennial oscillatory variation in the low-latitude and equatorial regions. This work provides a referable study of global atmospheric circulation and demonstrates the impacts of solar activity on global atmospheric circulation.

The jet stream and climate change

This article introduces factors contributing significantly to climate change that have been largely neglected in both the scientific and popular press. These factors have immediate implications for public policy directed at slowing, halting and even reversing climate change and its effects. This article argues that in addition to the known contributions made by greenhouse gasses, climate change is also driven by shifts in the patterns of global atmospheric circulation which are influenced by persistent, large-scale vortices caused by the wake turbulence left by commercial air traffic. Because this traffic is highly concentrated along the most frequently traveled routes, the vortices aircraft create have transformed into semi-permanent atmospheric circulation which have widespread effects on how the atmosphere traps and releases heat. It is also possible that these changes alter the loss of water from the atmosphere. This would endanger all life on earth, not just the human population.

Inconsistent Global Kinetic Energy Spectra in Reanalyses and Models

Global upper tropospheric kinetic energy (KE) spectra in several global atmospheric circulation datasets are examined. The datasets considered include the ERA-Interim, JRA-55, and ERA5 reanalyses and two versions of NOAA-GFS analyses at horizontal resolutions ranging from 0.7° to 0.12°. The mesoscale portions of the spectra are found to be highly inconsistent. This is shown to be mainly due to inconsistencies in the scale-dependent numerical damping and in the large contributions to the global mesoscale KE from the KE in convective regions and near orography.The spectra also generally have a steeper mesoscale slope than the -5/3 slope of the observational Nastrom-Gage spectrum pursued at many modeling centers. The sensitivity of the slope in global models to 1) stochastically perturbing diabatic tendencies and 2) decreasing the horizontal hyper-viscosity coefficient is explored in large ensembles of 10-day forecasts made with the NCEP-GFS (0.7° grid) model. Both changes lead to larger mesoscale KE and a flatter spectral slope. The effect is stronger in the modified hyper-viscosity experiment.These results show that (a) despite assimilating vastly more observations than used in the original Nastrom-Gage studies, current high-resolution global analyses still do not converge to a single “true” global mesoscale KE spectrum, and (b) model KE spectra can be made flatter not just by increasing model resolution but also by perturbing model physics and decreasing horizontal diffusion. Such sensitivities and lack of consensus on the spectral slope also raise the possibility that the true global mesoscale spectral slope may not be a precisely -5/3 slope.

Atmospheric scattering of energetic electrons from near-Earth space

In near-Earth space, the magnetosphere, energetic electrons (tens to thousands of kiloelectron volts) orbit around Earth, forming the radiation belts. When scattered by magnetospheric processes, these electrons precipitate to the upper atmosphere, where they deplete ozone, a radiatively active gas, modifying global atmospheric circulation. Relativistic electrons (those above a few hundred kiloelectron volts), can reach the lowest altitudes and have the strongest effects on the upper atmosphere; their loss from the magnetosphere is also important for space weather. Previous models have only considered magnetospheric scattering and precipitation of energetic electrons; atmospheric scattering of such electrons has not been adequately considered, principally due to lack of observations. Here we report the first observations of this process. We find that atmospherically-scattered energetic (relativistic) electrons form a low-intensity, persistent “drizzle”, whose integrated energy flux is comparable to (greater than) that of the more intense but ephemeral precipitation by magnetospheric scattering. Thus, atmospheric scattering of energetic electrons is important for global atmospheric circulation, radiation belt flux evolution, and the repopulation of the magnetosphere with lower-energy, secondary electrons.

Global reorganization of atmospheric circulation during Dansgaard-Oschger cycles

<p>Ice core records from Greenland provide evidence for multiple abrupt warming events recurring at millennial time scales during the last glacial interval. Although climate transitions strongly resembling these Dansgaard-Oeschger (DO) transitions have been identified in several speleothem records, our understanding of the climate and ecosystem impacts of the Greenland warming events in lower latitudes remains incomplete.</p><p>Here, we investigate the influence of DO transitions on the global atmospheric circulation pattern. We comprehensively analyse d18O changes during DO transitions in a globally distributed dataset of speleothems (SISALv2; Comas-Bru et al., 2020). Speleothem d18O signals mostly reflect changes in precipitation amount and moisture source. Thereby this proxy allows us to infer spatially resolved changes in global atmospheric dynamics that are characteristically linked to DO transitions. We confirm the previously proposed shift of the Intertropical Convergence Zone towards more northerly positions. In addition, we find evidence for a similar northward shift of the westerly winds of the Northern Hemisphere. Furthermore, we identify a decreasing trend in the transition amplitudes with increasing distances from the North Atlantic region. This confirms previous suggestions of this region being the core and origin of these past abrupt climate changes.</p><p> </p><p>References:</p><p>Comas-Bru et al., 2020, Earth System Science Data 12, 2579–2606</p><p> </p>

Global patterns of oceanic dust deposition during Pliocene-Pleistocene transitions

<p>The is a mounting evidence that global emissions of dust were significantly higher during glacial than interglacial periods of the Pleistocene, and probably the Pliocene epochs. this pattern is observed in records from the low and mid latitudes, albeit with a varying degree of amplitude. During these time periods spanning 4 million years, the Earth climate underwent major transitions, such as the initiation of the Northern Hemisphere Glaciations and the Mid Pleistocene Transition. In parallel, dust transport and deposition on the oceans might have underwent stepwise increases, mainly during glacials. However, it is not clear yet if such changes are representative of global or regional climate response. Thus, dust records in marine sediments reflect changes in the different processes that drive the emission, transport, and deposition of dust on the oceans. In here, we report a compilation of marine dust records spanning the Pliocene-Pleistocene from all the major ocean basins. The synthesis of dust records on a global scale allows the identification of common patterns of variability and drivers. We analyse the data to infer changes in the global atmospheric circulation on orbital time scale, and to assess its meridional and zonal response during major climate transitions since the Pliocene.</p>

Jetwash-induced vortices and climate change

This article introduces factors contributing significantly to climate change that have been largely neglected in both the scientific and popular press. These factors have immediate implications for public policy directed at slowing, halting and even reversing climate change and its effects. This article argues that in addition to the known contributions made by greenhouse gasses, climate change is also driven by shifts in the patterns of global atmospheric circulation which are influenced by persistent, large-scale vortices caused by the wake turbulence left by commercial air traffic. Because this traffic is highly concentrated along the most frequently traveled routes, the vortices aircraft create have transformed into semi-permanent atmospheric circulation which have widespread effects on how the atmosphere traps and releases heat. It is also possible that these changes alter the loss of water from the atmosphere. This would endanger all life on earth, not just the human population.

A nonstationary analysis for investigating the multiscale variability of extreme surges: case of the English Channel coasts

This research examines the nonstationary dynamics of extreme surges along the English Channel coasts and seeks to make their connection to the climate patterns at different timescales by the use of a detailed spectral analysis in order to gain insights into the physical mechanisms relating the global atmospheric circulation to the local-scale variability of the monthly extreme surges. This variability highlights different oscillatory components from the interannual (∼1.5, ∼2–4, ∼5–8 years) to the interdecadal (∼12–16 years) scales with mean explained variances of ∼25 %–32 % and ∼2 %–4 % of the total variability, respectively. Using the two hypotheses that the physical mechanisms of the atmospheric circulation change according to the timescales and their connection with the local variability improves the prediction of the extremes, we have demonstrated statistically significant relationships of ∼1.5, ∼2–4, ∼5–8 and 12–16 years with the different climate oscillations of sea level pressure, zonal wind, North Atlantic Oscillation and Atlantic Multidecadal Oscillation, respectively. Such physical links have been used to implement the parameters of the time-dependent generalized extreme value (GEV) distribution models. The introduced climate information in the GEV parameters has considerably improved the prediction of the different timescales of surges with an explained variance higher than 60 %. This improvement exhibits their non-linear relationship with the large-scale atmospheric circulation.