3,776 research outputs found
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Stratospheric dynamics and midlatitude jets under geoengineering with space mirrors and sulfate and titania aerosols
The impact on the dynamics of the stratosphere of three approaches to geoengineering by solar radiation management is investigated using idealized simulations of a global climate model. The approaches are geoengineering with sulfate aerosols, titania aerosols, and reduction in total solar irradiance (representing mirrors placed in space). If it were possible to use stratospheric aerosols to counterbalance the surface warming produced by a quadrupling of atmospheric carbon dioxide concentrations, tropical lower stratospheric radiative heating would drive a thermal wind response which would intensify the stratospheric polar vortices. In the Northern Hemisphere this intensification results in strong dynamical cooling of the polar stratosphere. Northern Hemisphere stratospheric sudden warming events become rare (one and two in 65 years for sulfate and titania, respectively). The intensification of the polar vortices results in a poleward shift of the tropospheric midlatitude jets in winter. The aerosol radiative heating enhances the tropical upwelling in the lower stratosphere, influencing the strength of the Brewer-Dobson circulation. In contrast, solar dimming does not produce heating of the tropical lower stratosphere, and so there is little intensification of the polar vortex and no enhanced tropical upwelling. The dynamical response to titania aerosol is qualitatively similar to the response to sulfate
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Wintertime North American weather regimes and the Arctic stratospheric polar vortex
The impact of the Arctic stratospheric polar vortex on persistent weather regimes over North America is so far under-explored. Here we show the relationship between four wintertime North American weather regimes and the stratospheric vortex strength using reanalysis data. We find that the strength of the vortex significantly affects the behavior of the regimes. Whilst a regime associated with Greenland blocking is strongly favored following weak vortex events, it is not the primary regime associated with a widespread, elevated risk of extreme cold in North America. Instead, we find that the regime most strongly associated with widespread extremely cold weather does not show a strong dependency on the strength of the lower-stratospheric zonal-mean zonal winds. We also suggest that stratospheric vortex morphology may be particularly important for cold air outbreaks during this regime
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Meteorological source variability in atmospheric gravity wave parameters derived from a tropical infrasound station
Gravity waves are an important part of the momentum budget of the atmosphere. Despite this, parameterizations of gravity wave spectra in atmospheric models are poorly constrained. Gravity waves are formed by jet streams, flow over topography and convection, all of which produce pressure perturbations as they propagate over the Earthâs surface, detectable by microbarometer arrays used for sensing infrasound. In this study, observations of gravity waves between 2007 and 2011 at an infrasound station in the Ivory Coast, West Africa are combined with meteorological data to calculate parameters such as intrinsic phase speed and wavenumber. Through spectral analysis, the seasonal and daily variations in all gravity wave parameters are examined. The gravity wave back azimuth varies with the migration of the Inter-Tropical Convergence Zone, a region of intense convection, supporting previous studies. Daily variations in gravity wave arrivals at the station can be linked to two distinct convective cycles over the land and ocean. This was achieved by combining the gravity wave parameters with lightning strikes detected by the Met Officeâs Arrival Time Difference lightning detection system. Noise generated by turbulence in the middle of the day was found to attenuate smaller pressure amplitude gravity waves, artificially amplifying the daily variations in some gravity wave parameters. Detection of daily and seasonal variations in gravity wave parameters has the potential be used to improve the representation of gravity wave spectra in atmospheric models
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Chilean wildfires: probabilistic prediction, emergency response and public communication
The 2016/17 wildfire season in Chile was the worst on record, burning more than 600,000 hectares. Whilst wildfires are an important natural process in some areas of Chile supporting its diverse ecosystems, wildfires are also one of the biggest threats to Chileâs unique biodiversity and itâs timber and wine industries. They also pose a danger to human life and property due to the sharp wildland-urban interface that exists in many Chilean towns and cities. Wildfires are however difficult to predict due to the combination of physical (meteorology, vegetation and fuel condition), and human (population density and awareness level) factors. Most Chilean wildfires are started due to accidental ignition by humans. This accidental ignition could be minimized if an effective wildfire warning system alerted the population to the heightened danger of wildfires in certain locations and meteorological conditions. Here we demonstrate the design of a novel probabilistic wildfire prediction system. The system uses ensemble forecast meteorological data together with a longtime series of fire products derived from Earth Observation to predict not only fire occurrence, but in addition, how intense wildfires could be. The system provides wildfire risk estimation and associated uncertainty for up to 6 days in advance, and communicates it to a variety of end users. The advantage of this probabilistic wildfire warning system over deterministic systems is that it allows users to assess the confidence of a forecast and thus make more informed decisions regarding resource allocation and forest management. The approach used in this study could easily be adapted to communicate other probabilistic forecasts of natural hazards
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Understanding representations of uncertainty, an eye-tracking study â Part 1: The effect of anchoring
Geoscience communicators must think carefully about how
uncertainty is represented and how users may interpret these
representations. Doing so will help communicate risk more effectively, which
can elicit appropriate responses. Communication of uncertainty is not just a
geosciences problem; recently, communication of uncertainty has come to the
forefront over the course of the COVID-19 pandemic, but the lessons learned
from communication during the pandemic can be adopted across geosciences as
well. To test interpretations of environmental forecasts with uncertainty,
a decision task survey was administered to 65 participants who saw different
hypothetical forecast representations common to presentations of
environmental data and forecasts: deterministic, spaghetti plot with and
without a median line, fan plot with and without a median line, and box plot
with and without a median line. While participants completed the survey,
their eye movements were monitored with eye-tracking software. Participants'
eye movements were anchored to the median line, not focusing on possible
extreme values to the same extent as when no median line was present.
Additionally, participants largely correctly interpreted extreme values from
the spaghetti and fan plots, but misinterpreted extreme values from the box
plot, perhaps because participants spent little time fixating on the key.
These results suggest that anchoring lines, such as median lines, should
only be used where users should be guided to particular values and where
extreme values are not as important in data interpretation. Additionally,
fan or spaghetti plots should be considered instead of box plots to reduce
misinterpretation of extreme values. Further study on the role of expertise
and the change in eye movements across the graph area and key is explored in more detail in the companion paper to this study (Williams et al., 2023; hereafter Part 2).</p
The potential to narrow uncertainty in projections of stratospheric ozone over the 21st century
Future stratospheric ozone concentrations will be determined both by changes in the concentration of ozone depleting substances (ODSs) and by changes in stratospheric and tropospheric climate, including those caused by changes in anthropogenic greenhouse gases (GHGs). Since future economic development pathways and resultant emissions of GHGs are uncertain, anthropogenic climate change could be a significant source of uncertainty for future projections of stratospheric ozone. In this pilot study, using an "ensemble of opportunity" of chemistry-climate model (CCM) simulations, the contribution of scenario uncertainty from different plausible emissions pathways for ODSs and GHGs to future ozone projections is quantified relative to the contribution from model uncertainty and internal variability of the chemistry-climate system. For both the global, annual mean ozone concentration and for ozone in specific geographical regions, differences between CCMs are the dominant source of uncertainty for the first two-thirds of the 21st century, up-to and after the time when ozone concentrations return to 1980 values. In the last third of the 21st century, dependent upon the set of greenhouse gas scenarios used, scenario uncertainty can be the dominant contributor. This result suggests that investment in chemistry-climate modelling is likely to continue to refine projections of stratospheric ozone and estimates of the return of stratospheric ozone concentrations to pre-1980 levels
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Understanding representations of uncertainty, an eye-tracking study â Part 2: The effect of expertise
As the ability to make predictions regarding uncertainty information
representing natural hazards increases, an important question for those
designing and communicating hazard forecasts is how visualizations of
uncertainty influence understanding amongst the intended, potentially
varied, target audiences. End-users have a wide range of differing expertise
and backgrounds, possibly influencing the decision-making process they
undertake for a given forecast presentation. Our previous, Part 1 study
(Mulder et al., 2023) examined how the presentation of uncertainty
information influenced end-user decision making. Here, we shift the focus to
examine the decisions and reactions of participants with differing areas of expertise
(meteorology, psychology, and graphic-communication students) when presented
with varied hypothetical forecast representations (boxplot, fan plot, or
spaghetti plot with and without median lines) using the same eye-tracking
methods and experiments. Participants made decisions about a fictional
scenario involving the choices between ships of different sizes in the face
of varying ice thickness forecasts. Eye movements to the graph area and key
and how they changed over time (early, intermediate, and later viewing
periods) were examined. More fixations (maintained gaze on one location)
and more fixation time were spent on the graph and key during early and
intermediate periods of viewing, particularly for boxplots and fan plots.
The inclusion of median lines led to less fixations being made on all graph
types during early and intermediate viewing periods. No difference in eye
movement behaviour was found due to expertise; however, those with greater
expertise were more accurate in their decisions, particularly during more
difficult scenarios. Where scientific producers seek to draw users to the
central estimate, an anchoring line can significantly reduce cognitive load,
leading both experts and non-experts to make more rational decisions. When
asking users to consider extreme scenarios or uncertainty, different prior
expertise can lead to significantly different cognitive loads for processing
information, with an impact on one's ability to make appropriate decisions.</p
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Trends in Austral jet position in ensembles of high- and low-top CMIP5 models
Trends in the position of the DJF Austral jet have been analysed for multi-model ensemble simulations of a subset of high- and low-top models for the periods 1960-2000, 2000-2050, and 2050-2098 under the CMIP5 historical, RCP4.5, and RCP8.5 scenarios. Comparison with ERA-Interim,
CFSR and the NCEP/NCAR reanalysis shows that the DJF and annual mean jet positions in CMIP5 models are equatorward of reanalyses for the 1979-2006 mean. Under the RCP8.5 scenario, the mean jet position in the high-top models moves 3 degrees poleward of its 1860-1900 position by
2098, compared to just over 2 degrees for the low-top models.
Changes in jet position are linked to changes in the meridional temperature gradient. Compared to low-top models, the high-top models predict greater warming in the tropical upper troposphere due to
increased greenhouse gases for all periods considered: up to 0.28 K/decade more in the period 2050-2098 under the RCP8.5 scenario. Larger polar lower-stratospheric cooling is seen in high-top models: -1.64 K/decade compared to -1.40 K/decade in the period 1960-2000, mainly in response to ozone depletion, and -0.41 K/decade compared to -0.12 K/decade in the period 2050-2098, mainly in response to increases in greenhouse gases.
Analysis suggests that there may be a linear relationship between the trend in jet position and meridional temperature gradient, even under strong forcing. There were no clear indications of an approach to a geometric limit on the absolute magnitude of the poleward shift by 2100
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Comparison of co-located independent ground-based middle atmospheric wind and temperature measurements with numerical weather prediction models
High-resolution, ground-based and independent observations including co-located windradiometer, lidar stations, and infrasound instruments are used to evaluate the accuracy of general circulationmodels and data-constrained assimilation systems in the middle atmosphere at northern hemispheremidlatitudes. Systematic comparisons between observations, the European Centre for Medium-Range WeatherForecasts (ECMWF) operational analyses including the recent Integrated Forecast System cycles 38r1 and 38r2,the NASAâs Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalyses, and thefree-running climate Max Planck InstituteâEarth System ModelâLow Resolution (MPI-ESM-LR) are carried out inboth temporal and spectral dom ains. We ïŹnd that ECMWF and MERRA are broadly consistent with lidar and windradiometer measurements up to ~40 km. For both temperature and horizontal wind components, deviationsincrease with altitude as the assimilated observations become sparser. Between 40 and 60 km altitude, thestandard deviation of the mean difference exceeds 5 K for the temperature and 20 m/s for the zonal wind. Thelargest deviations are observed in winter when the variability from large-scale planetary waves dominates.Between lidar data and MPI-ESM-LR, there is an overall agreement in spectral amplitude down to 15â20 days. Atshorter time scales, the variability is lacking in the model by ~10 dB. Infrasound observations indicate a generalgood agreement with ECWMF wind and temperature products. As such, this study demonstrates the potentialof the infrastructure of the Atmospheric Dynamics Research Infrastructure in Europe project that integratesvarious measurements and provides a quantitative understanding of stratosphere-troposphere dynamicalcoupling for numerical weather prediction applications
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A risk-based framework for assessing the effectiveness of stratospheric aerosol geoengineering
Open Access journalCopyright: © 2014 Ferraro et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Geoengineering by stratospheric aerosol injection has been proposed as a policy response to warming from human emissions of greenhouse gases, but it may produce unequal regional impacts. We present a simple, intuitive risk-based framework for classifying these impacts according to whether geoengineering increases or decreases the risk of substantial climate change, with further classification by the level of existing risk from climate change from increasing carbon dioxide concentrations. This framework is applied to two climate model simulations of geoengineering counterbalancing the surface warming produced by a quadrupling of carbon dioxide concentrations, with one using a layer of sulphate aerosol in the lower stratosphere, and the other a reduction in total solar irradiance. The solar dimming model simulation shows less regional inequality of impacts compared with the aerosol geoengineering simulation. In the solar dimming simulation, 10% of the Earth's surface area, containing 10% of its population and 11% of its gross domestic product, experiences greater risk of substantial precipitation changes under geoengineering than under enhanced carbon dioxide concentrations. In the aerosol geoengineering simulation the increased risk of substantial precipitation change is experienced by 42% of Earth's surface area, containing 36% of its population and 60% of its gross domestic product.Natural Environment Research Council (NERC
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