457 research outputs found
Modeling the Frozen-In Anticyclone in the 2005 Arctic Summer Stratosphere
Immediately following the breakup of the 2005 Arctic spring stratospheric vortex, a tropical air mass, characterized by low potential vorticity (PV) and high nitrous oxide (N2O), was advected poleward and became trapped in the easterly summer polar vortex. This feature, known as a "Frozen-In Anticyclone (FrIAC)", was observed in Earth Observing System (EOS) Aura Microwave Limb Sounder (MLS) data to span the potential temperature range from approximately 580 to 1100 K (approximately 25 to 40 km altitude) and to persist from late March to late August 2005. This study compares MLS N2O observations with simulations from the Global Modeling Initiative (GMI) chemistry and transport model, the GEOS-5/MERRA Replay model, and the VanLeer Icosahedral Triangular Advection isentropic transport model to elucidate the processes involved in the lifecycle of the FrIAC which is here divided into three distinct phases. During the "spin-up phase" (March to early April), strong poleward flow resulted in a tight isolated anticyclonic vortex at approximately 70-90 deg N, marked with elevated N2O. GMI, Replay, and VITA all reliably simulted the spin-up of the FrIAC, although the GMI and Replay peak N2O values were too low. The FrIAC became trapped in the developing summer easterly flow and circulated around the polar region during the "anticyclonic phase" (early April to the end of May). During this phase, the FrIAC crossed directly over the pole between the 7th and 14th of April. The VITA and Replay simulations transported the N2O anomaly intact during this crossing, in agreement with MLS, but unrealistic dispersion of the anomaly occurred in the GMI simulation due to excessive numerical mixing of the polar cap. The vortex associated with the FrIAC was apparently resistant to the weak vertical hear during the anticyclonic phase, and it thereby protected the embedded N20 anomaly from stretching. The vortex decayed in late May due to diabatic processes, leaving the N2O anomaly exposed to horizontal and vertical wind shears during the "shearing phase" (June to August). The observed lifetime of the FrIAC during this phase is consistent with time-scales calculated from the ambient horizontal and vertical wind shear. Replay maintained the horizontal structure of the N2O anomaly similar to NILS well into August. The VITA simulation also captured the horizontal structure of the FrIAC during this phase, but VITA eventually developed fine-scale N2O structure not observed in MLS data
Multi-model simulations of the impact of international shipping on Atmospheric Chemistry and Climate in 2000 and 2030
The global impact of shipping on atmospheric chemistry and radiative forcing, as well as the associated uncertainties, have been quantified using an ensemble of ten state-of-the-art atmospheric chemistry models and a predefined set of emission data. The analysis is performed for present-day conditions ( year 2000) and for two future ship emission scenarios. In one scenario ship emissions stabilize at 2000 levels; in the other ship emissions increase with a constant annual growth rate of 2.2% up to 2030 ( termed the "Constant Growth Scenario" (CGS)). Most other anthropogenic emissions follow the IPCC ( Intergovernmental Panel on Climate Change) SRES ( Special Report on Emission Scenarios) A2 scenario, while biomass burning and natural emissions remain at year 2000 levels. An intercomparison of the model results with observations over the Northern Hemisphere (25 degrees - 60 degrees N) oceanic regions in the lower troposphere showed that the models are capable to reproduce ozone (O-3) and nitrogen oxides (NOx= NO+ NO2) reasonably well, whereas sulphur dioxide (SO2) in the marine boundary layer is significantly underestimated. The most pronounced changes in annual mean tropospheric NO2 and sulphate columns are simulated over the Baltic and North Seas. Other significant changes occur over the North Atlantic, the Gulf of Mexico and along the main shipping lane from Europe to Asia, across the Red and Arabian Seas. Maximum contributions from shipping to annual mean near-surface O-3 are found over the North Atlantic ( 5 - 6 ppbv in 2000; up to 8 ppbv in 2030). Ship contributions to tropospheric O3 columns over the North Atlantic and Indian Oceans reach 1 DU in 2000 and up to 1.8 DU in 2030. Tropospheric O-3 forcings due to shipping are 9.8 +/- 2.0 mW/m(2) in 2000 and 13.6 +/- 2.3 mW/m(2) in 2030. Whilst increasing O-3, ship NOx simultaneously enhances hydroxyl radicals over the remote ocean, reducing the global methane lifetime by 0.13 yr in 2000, and by up to 0.17 yr in 2030, introducing a negative radiative forcing. The models show future increases in NOx and O-3 burden which scale almost linearly with increases in NOx emission totals. Increasing emissions from shipping would significantly counteract the benefits derived from reducing SO2 emissions from all other anthropogenic sources under the A2 scenario over the continents, for example in Europe. Globally, shipping contributes 3% to increases in O-3 burden between 2000 and 2030, and 4.5% to increases in sulphate under A2/CGS. However, if future ground based emissions follow a more stringent scenario, the relative importance of ship emissions will increase. Inter-model differences in the simulated O-3 contributions from ships are significantly smaller than estimated uncertainties stemming from the ship emission inventory, mainly the ship emission totals, the distribution of the emissions over the globe, and the neglect of ship plume dispersion
Large-scale transport into the Arctic: the roles of the midlatitude jet and the Hadley Cell
Transport from the Northern Hemisphere (NH) midlatitudes to the
Arctic plays a crucial role in determining the abundance of trace gases and
aerosols that are important to Arctic climate via impacts on radiation and
chemistry. Here we examine this transport using an idealized tracer with a
fixed lifetime and predominantly midlatitude land-based sources in models
participating in the Chemistry Climate Model Initiative (CCMI). We show that
there is a 25 %–45 % difference in the Arctic concentrations of this tracer
among the models. This spread is correlated with the spread in the location
of the Pacific jet, as well as the spread in the location of the Hadley Cell
(HC) edge, which varies consistently with jet latitude. Our results suggest
that it is likely that the HC-related zonal-mean meridional transport rather
than the jet-related eddy mixing is the major contributor to the inter-model
spread in the transport of land-based tracers into the Arctic. Specifically,
in models with a more northern jet, the HC generally extends further north
and the tracer source region is mostly covered by surface southward flow
associated with the lower branch of the HC, resulting in less efficient
transport poleward to the Arctic. During boreal summer, there are poleward
biases in jet location in free-running models, and these models likely
underestimate the rate of transport into the Arctic. Models using specified
dynamics do not have biases in the jet location, but do have biases in the
surface meridional flow, which may result in differences in transport into
the Arctic. In addition to the land-based tracer, the midlatitude-to-Arctic
transport is further examined by another idealized tracer with zonally
uniform sources. With equal sources from both land and ocean, the inter-model
spread of this zonally uniform tracer is more related to variations in
parameterized convection over oceans rather than variations in HC extent,
particularly during boreal winter. This suggests that transport of land-based
and oceanic tracers or aerosols towards the Arctic differs in pathways and
therefore their corresponding inter-model variabilities result from different
physical processes.</p
Howard's War on Terror: A Conceivable, Communicable and Coercive Foreign Policy Discourse
This article explores the relationship between language and political possibility. It is argued that John Howard’s language from 11 September 2001 to mid 2003 helped to enable the ‘War on Terror’ in an Australian context in three principal ways. Firstly, through contingent and contestable constructions of Australia, the world and their relationship, Howard’s language made interventionism conceivable. Secondly, emphasising shared values, mateship and mutual sacrifice in war, Howard embedded his foreign policy discourse in the cultural terrain of ‘mainstream Australia’, specifically framing a foreign policy discourse that was communicable to ‘battlers’ and disillusioned ‘Hansonites’. Thirdly, positioning alternatives as ‘un-Australian’, Howard’s language was particularly coercive, silencing potential oppositional voices
Interstellar OH+, H2O+ and H3O+ along the sight-line to G10.6-0.4
We report the detection of absorption lines by the reactive ions OH+, H2O+
and H3O+ along the line of sight to the submillimeter continuum source
G10.60.4 (W31C). We used the Herschel HIFI instrument in dual beam switch
mode to observe the ground state rotational transitions of OH+ at 971 GHz, H2O+
at 1115 and 607 GHz, and H3O+ at 984 GHz. The resultant spectra show deep
absorption over a broad velocity range that originates in the interstellar
matter along the line of sight to G10.60.4 as well as in the molecular gas
directly associated with that source. The OH+ spectrum reaches saturation over
most velocities corresponding to the foreground gas, while the opacity of the
H2O+ lines remains lower than 1 in the same velocity range, and the H3O+ line
shows only weak absorption. For LSR velocities between 7 and 50 kms we
estimate total column densities of (OH+) cm,
(H2O+) cm and (H3O+) cm. These detections confirm the role of O and OH in
initiating the oxygen chemistry in diffuse molecular gas and strengthen our
understanding of the gas phase production of water. The high ratio of the OH+
by the H2O+ column density implies that these species predominantly trace
low-density gas with a small fraction of hydrogen in molecular form
Herschel/HIFI observations of interstellar OH+ and H2O+ towards W49N: a probe of diffuse clouds with a small molecular fraction
We report the detection of absorption by interstellar hydroxyl cations and
water cations, along the sight-line to the bright continuum source W49N. We
have used Herschel's HIFI instrument, in dual beam switch mode, to observe the
972 GHz N = 1 - 0 transition of OH+ and the 1115 GHz 1(11) - 0(00) transition
of ortho-H2O+. The resultant spectra show absorption by ortho-H2O+, and strong
absorption by OH+, in foreground material at velocities in the range 0 to 70
km/s with respect to the local standard of rest. The inferred OH+/H2O+
abundance ratio ranges from ~ 3 to ~ 15, implying that the observed OH+ arises
in clouds of small molecular fraction, in the 2 - 8% range. This conclusion is
confirmed by the distribution of OH+ and H2O+ in Doppler velocity space, which
is similar to that of atomic hydrogen, as observed by means of 21 cm absorption
measurements, and dissimilar from that typical of other molecular tracers. The
observed OH+/H abundance ratio of a few E-8 suggests a cosmic ray ionization
rate for atomic hydrogen of (0.6 - 2.4) E-16 s-1, in good agreement with
estimates inferred previously for diffuse clouds in the Galactic disk from
observations of interstellar H3+ and other species.Comment: Accepted for publication in A&A Letter
Assessing the Effects of Personal Characteristics and Context on U.S. House Speakers’ Leadership Styles, 1789-2006
Research on congressional leadership has been dominated in recent decades by contextual interpretations that see leaders’ behavior as best explained by the environment in which they seek to exercise leadership—particularly, the preference homogeneity and size of their party caucus. The role of agency is thus discounted, and leaders’ personal characteristics and leadership styles are underplayed. Focusing specifically on the speakers of the U.S. House of Representatives from the first to the 110th Congress, we construct measures of each speaker’s commitment to comity and leadership assertiveness. We find the scores reliable and then test the extent to which a speaker’s style is the product of both political context and personal characteristics. Regression estimates on speakers’ personal assertiveness scores provide robust support for a context-plus-personal characteristics explanation, whereas estimates of their comity scores show that speakers’ personal backgrounds trump context
Detection of interstellar oxidaniumyl: abundant H2O+ towards the star-forming regions DR21, Sgr B2, and NGC6334
We identify a prominent absorption feature at 1115 GHz, detected in first
HIFI spectra towards high-mass star-forming regions, and interpret its
astrophysical origin. The characteristic hyperfine pattern of the H2O+
ground-state rotational transition, and the lack of other known low-energy
transitions in this frequency range, identifies the feature as H2O+ absorption
against the dust continuum background and allows us to derive the velocity
profile of the absorbing gas. By comparing this velocity profile with velocity
profiles of other tracers in the DR21 star-forming region, we constrain the
frequency of the transition and the conditions for its formation. In DR21, the
velocity distribution of H2O+ matches that of the [CII] line at 158\mu\m and of
OH cm-wave absorption, both stemming from the hot and dense clump surfaces
facing the HII-region and dynamically affected by the blister outflow. Diffuse
foreground gas dominates the absorption towards Sgr B2. The integrated
intensity of the absorption line allows us to derive lower limits to the H2O+
column density of 7.2e12 cm^-2 in NGC 6334, 2.3e13 cm^-2 in DR21, and 1.1e15
cm^-2 in Sgr B2.Comment: Accepted for publication in A&
Smokers' recall of Australian graphic cigarette packet warnings & awareness of associated health effects, 2005-2008
Extent: 11p.Background: In 2006, Australia introduced graphic cigarette packet warnings. The new warnings include one of 14 pictures, many depicting tobacco-related pathology. The warnings were introduced in two sets; Set A in March and Set B from November. This study explores their impact on smokers’ beliefs about smoking related illnesses. This study also examines the varying impact of different warnings, to see whether warnings with visceral images have greater impact on smokers’ beliefs than other images. Methods: Representative samples of South Australian smokers were interviewed in four independent cross-sectional omnibus surveys; in 2005 (n = 504), 2006 (n = 525), 2007 (n = 414) and 2008 (n = 464). Results: Unprompted recall of new graphic cigarette warnings was high in the months following their introduction, demonstrating that smokers’ had been exposed to them. Smokers also demonstrated an increase in awareness about smoking-related diseases specific to the warning messages. Warnings that conveyed new information and had emotive images demonstrated greater impact on recall and smokers’ beliefs than more familiar information and less emotive images. Conclusions: Overall graphic pack warnings have had the intended impact on smokers. Some have greater impact than others. The implications for policy makers in countries introducing similar warnings are that fresh messaging and visceral images have the greatest impact.Caroline L Miller, Pascale G Quester, David J Hill and Janet E Hille
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