31 research outputs found
Climate change and growing megacities: hazards and vulnerability
This paper is a review of geophysical and climatic trends associated with extreme weather events and natural hazards, their implications for urban areas and the effects of continued environmental modification due to urban expansion. It discusses how urban design, technological development and societal behaviour can either ameliorate or worsen climate-induced hazards in urban areas. Pressures – ranging from excessive rainfall causing urban flooding to urban temperature extremes driving air pollution – require more attention to understand, model and predict changes in hazards in urban areas. It concludes that involving different techniques for data analysis and system modelling is more appropriate for practical decision-making than a purely reductionist approach. Successfully determining the future environment of megacities will, however, require joint action with societally informed decision makers, grounded in sound scientific achievements
Stratosphere-troposphere transport in a numerical simulation of midlatitude convection
The transport of stratospheric air deep into the troposphere via convection is
investigated numerically using the UK Met Office Unified Model. A convective system
that formed on 27 June 2004 near southeast England, in the vicinity an upper level
potential vorticity anomaly and a lowered tropopause, provides the basis for analysis.
Transport is diagnosed using a stratospheric tracer that can either be passed through or
withheld from the model’s convective parameterization scheme. Three simulations are
performed at increasingly finer resolutions, with horizontal grid lengths of 12, 4, and 1 km.
In the 12 and 4 km simulations, tracer is transported deeply into the troposphere by the
parameterized convection. In the 1 km simulation, for which the convective
parameterization is disengaged, deep transport is still accomplished but with a much
smaller magnitude. However, the 1 km simulation resolves stirring along the tropopause
that does not exist in the coarser simulations. In all three simulations, the concentration of
the deeply transported tracer is small, three orders of magnitude less than that of the
shallow transport near the tropopause, most likely because of the efficient dilution of
parcels in the lower troposphere
Simulating meteorological profiles to study noise propagation from freeways
Forecasts of noise pollution from a highway line segment noise source are obtained from a sound propagation model utilizing effective sound speed profiles derived from a Numerical Weather Prediction (NWP) limited area forecast with 1 km horizontal resolution and near-ground vertical resolution finer than 20 m. Methods for temporal along with horizontal and vertical spatial nesting are demonstrated within the NWP model for maintaining forecast feasibility. It is shown that vertical nesting can improve the prediction of finer structures in near-ground temperature and velocity profiles, such as morning temperature inversions and low level jet-like features. Accurate representation of these features is shown to be important for modeling sound refraction phenomena and for enabling accurate noise assessment. Comparisons are made using the parabolic equation model for predictions with profiles derived from NWP simulations and from field experiment observations during mornings on November 7 and 8, 2006 in Phoenix, Arizona. The challenges faced in simulating accurate meteorological profiles at high resolution for sound propagation applications are highlighted and areas for possible improvement are discussed
Seasonal hydroclimatic impacts of Sun Corridor expansion
Conversion of natural to urban land forms imparts influence on local and regional hydroclimate via modification of the surface energy and water balance, and consideration of such effects due to rapidly expanding megapolitan areas is necessary in light of the growing global share of urban inhabitants. Based on a suite of ensemble-based, multi-year simulations using the Weather Research and Forecasting (WRF) model, we quantify seasonally varying hydroclimatic impacts of the most rapidly expanding megapolitan area in the US: Arizona’s Sun Corridor, centered upon the Greater Phoenix metropolitan area. Using a scenario-based urban expansion approach that accounts for the full range of Sun Corridor growth uncertainty through 2050, we show that built environment induced warming for the maximum development scenario is greatest during the summer season (regionally averaged warming over AZ exceeds 1 °C). Warming remains significant during the spring and fall seasons (regionally averaged warming over AZ approaches 0.9 °C during both seasons), and is least during the winter season (regionally averaged warming over AZ of 0.5 °C). Impacts from a minimum expansion scenario are reduced, with regionally averaged warming ranging between 0.1 and 0.3 °C for all seasons except winter, when no warming impacts are diagnosed. Integration of highly reflective cool roofs within the built environment, increasingly recognized as a cost-effective option intended to offset the warming influence of urban complexes, reduces urban-induced warming considerably. However, impacts on the hydrologic cycle are aggravated via enhanced evapotranspiration reduction, leading to a 4% total accumulated precipitation decrease relative to the non-adaptive maximum expansion scenario. Our results highlight potentially unintended consequences of this adaptation approach within rapidly expanding megapolitan areas, and emphasize the need for undeniably sustainable development paths that account for hydrologic impacts in addition to continued focus on mean temperature effects
Mixing layer formation near the tropopause due to gravity wave-critical level interactions in a cloud-resolving model
10.1175/JAS-3289.1Journal of the Atmospheric Sciences61243112-312
Observation and simulation of wave breaking in the southern hemispheric stratosphere during VORCORE
An interesting occurrence of a Rossby wave breaking event observed during the
VORCORE experiment is presented and explained. Twenty-seven balloons were
launched inside the Antarctic polar vortex. Almost all of these balloons
evolved in the stratosphere around 500K within the vortex, except the one
launched on 28 October 2005. In this case, the balloon was caught within a
tongue of high potential vorticity (PV), and was ejected from the polar
vortex. The evolution of this event is studied for the period between 19 and
25 November 2005. It is found that at the beginning of this period, the polar
vortex experienced distortions due to the presence of Rossby waves. Then,
these waves break and a tongue of high PV develops. On 25 November, the
tongue became separated from the vortex and the balloon was ejected into the
surf zone. Lagrangian simulations demonstrate that the air masses surrounding
the balloon after its ejection were originating from the vortex edge. The
wave breaking and the development of the tongue are confined within a region
where a planetary Quasi-Stationary Wave 1 (QSW1) induces wind speeds with
weaker values. The QSW1 causes asymmetry in the wind speed and the horizontal
PV gradient along the edge of the polar vortex, resulting in a localized jet.
Rossby waves with smaller scales propagating on top of this jet amplify as
they enter the jet exit region and then break. The role of the QSW1 on the
formation of the weak flow conditions that caused the non-linear wave
breaking observed near the vortex edge is confirmed by three-dimensional
numerical simulations using forcing with and without the contribution of the
QSW1