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991.
Meng-Dawn Cheng 《Journal of Atmospheric Chemistry》2018,75(1):1-16
Although a large volume of monitoring and computer simulation data exist for global coverage of HF, study of HF in the troposphere is still limited to industry whose primary interest is the safety and risk assessment of HF release because it is a toxic gas. There is very limited information on atmospheric chemistry, emission sources, and the behavior of HF in the environment. We provide a comprehensive review on the atmospheric chemistry of HF, modeling the reactions and transport of HF in the atmosphere, the removal processes in the vertical layer immediately adjacent to the surface (up to approximately 500 m) and recommend research needed to improve our understanding of atmospheric chemistry of HF in the troposphere. The atmospheric chemistry, emissions, and surface boundary layer transport of hydrogen fluoride (HF) are summarized. Although HF is known to be chemically reactive and highly soluble, both factors affect transport and removal in the atmosphere, the chemistry can be ignored when the HF concentration is at a sufficiently low level (e.g., 10 ppmv). At a low concentration, the capability for HF to react in the atmosphere is diminished and therefore the species can be mathematically treated as inert during the transport. At a sufficiently high concentration of HF (e.g., kg/s release rate and thousands of ppm), however, HF can go through a series of rigorous chemical reactions including polymerization, depolymerization, and reaction with water to form molecular complex. As such, the HF species cannot be considered as inert because the reactions could intimately influence the plume’s thermodynamic properties affecting the changes in plume temperature and density. The atmospheric residence time of HF was found to be less than four (4) days, and deposition (i.e., atmosphere to surface transport) is the dominant mechanism that controls the removal of HF and its oligomers from the atmosphere. The literature data on HF dry deposition velocity was relatively high compared to many commonly found atmospheric species such as ozone, sulfur dioxide, nitrogen oxides, etc. The global average of wet deposition velocity of HF was found to be zero based on one literature source. Uptake of HF by rain drops is limited by the acidity of the rain drops, and atmospheric particulate matter contributes negligibly to HF uptake. Finally, given that the reactivity of HF at a high release rate and elevated mole concentration cannot be ignored, it is important to incorporate the reaction chemistry in the near-field dispersion close to the proximity of the release source, and to incorporate the deposition mechanism in the far-field dispersion away from the release source. In other words, a hybrid computational scheme may be needed to address transport and atmospheric chemistry of HF in a range of applications. The model uncertainty will be limited by the precision of boundary layer parameterization and ability to accurately model the atmospheric turbulence. 相似文献
992.
To assess the potential impact of climate changes on pasture production in the North Island, New Zealand, eight climate scenarios
of increased temperature and increased (or decreased) rainfall were investigated by integrating a polynomial regression model
for pasture production with a Geographic Information System (GIS). The results indicated that the climate change scenarios
assuming an increase in temperature by 1–2°C and a rainfall change by −20 to +20% would have a very significant impact on
pasture production with a predicted pasture production variation from −46.2 to +51.9% compared with the normal climate from
1961–1990. Increased temperature would generally have a positive effect on pasture production in the south and southeast of
the North Island, and increased rainfall would have a positive effect in the central, south and southeast of the North Island
and a negative effect in the north of the North Island. The interaction of decreased rainfall and increased temperature would
have a negative impact for the whole North Island except some central areas with high rainfall. Relevant management practices
for coping with potential climate change are discussed. 相似文献
993.
Allison L. Steiner Jeremy S. Pal Sara A. Rauscher Jason L. Bell Noah S. Diffenbaugh Aaron Boone Lisa C. Sloan Filippo Giorgi 《Climate Dynamics》2009,33(6):869-892
Coupling of the Community Land Model (CLM3) to the ICTP Regional Climate Model (RegCM3) substantially improves the simulation
of mean climate over West Africa relative to an older version of RegCM3 coupled to the Biosphere Atmosphere Transfer Scheme
(BATS). Two 10-year simulations (1992–2001) show that the seasonal timing and magnitude of mean monsoon precipitation more
closely match observations when the new land surface scheme is implemented. Specifically, RegCM3–CLM3 improves the timing
of the monsoon advance and retreat across the Guinean Coast, and reduces a positive precipitation bias in the Sahel and Northern
Africa. As a result, simulated temperatures are higher, thereby reducing the negative temperature bias found in the Guinean
Coast and Sahel in RegCM3–BATS. In the RegCM3–BATS simulation, warmer temperatures in northern latitudes and wetter soils
near the coast create excessively strong temperature and moist static energy gradients, which shifts the African Easterly
Jet further north than observed. In the RegCM3–CLM3 simulation, the migration and position of the African Easterly Jet more
closely match reanalysis winds. This improvement is triggered by drier soil conditions in the RegCM3–CLM3 simulation and an
increase in evapotranspiration per unit precipitation. These results indicate that atmosphere–land surface coupling has the
ability to impact regional-scale circulation and precipitation in regions exhibiting strong hydroclimatic gradients. 相似文献
994.
Important factors governing the incompatible trends of annual pan evaporation: evidence from a small scale region 总被引:1,自引:0,他引:1
Many studies reported the coexisting trends of decreasing and increasing pan evaporation in some large scale regions. This
study proved that the coexisting trends also occurred in small scale region as well as in large scale region. To discover
the important factors governing the incompatible trends of annual pan evaporation, annual climatic data of ten meteorological
stations at the Liaohe Delta over recent 45 years were analyzed by the partial correlation analysis, and the results showed
the strongest statistically correlation between annual relative humidity and annual pan evaporation. Researches on two extreme
cases suggested there was obvious contrary trend between annual relative humidity and annual pan evaporation for one case,
in despite of slight contrary trend for another case. Generally, annual relative humidity most likely was an important factor
relating to the trend of annual pan evaporation. At the same time, an expanded urbanization and irrigation were seen around
these meteorological stations. Urbanization and irrigation exerted opposite effects on pan evaporation, they therefore were
speculated to be the ultimately inducements causing unbalanced relative humidity, and led to incompatible pan evaporation. 相似文献
995.
996.
Leonhard Gantner Vera Maurer Norbert Kalthoff Olga Kiseleva 《Boundary-Layer Meteorology》2017,162(3):475-502
A method to simulate characteristics of wind speed in the boundary layer of tropical cyclones in an idealized manner is developed and evaluated. The method can be used in a single-column modelling set-up with a planetary boundary-layer parametrization, or within large-eddy simulations (LES). The key step is to include terms in the horizontal velocity equations representing advection and centrifugal acceleration in tropical cyclones that occurs on scales larger than the domain size. Compared to other recently developed methods, which require two input parameters (a reference wind speed, and radius from the centre of a tropical cyclone) this new method also requires a third input parameter: the radial gradient of reference wind speed. With the new method, simulated wind profiles are similar to composite profiles from dropsonde observations; in contrast, a classic Ekman-type method tends to overpredict inflow-layer depth and magnitude, and two recently developed methods for tropical cyclone environments tend to overpredict near-surface wind speed. When used in LES, the new technique produces vertical profiles of total turbulent stress and estimated eddy viscosity that are similar to values determined from low-level aircraft flights in tropical cyclones. Temporal spectra from LES produce an inertial subrange for frequencies \(\gtrsim \)0.1 Hz, but only when the horizontal grid spacing \(\lesssim \)20 m. 相似文献
997.
Maciej Sadowski 《Climatic change》2008,90(4):443-451
Adopted by COP 10 (Dec 1/CP.10) and approved by the MOP1, the Buenos Aires programme of adaptation and response measures opens
doors to intensify preparations for expected climate change. By this decision the COP, requested the SBSTA to develop a structured
5-year programme of work of the SBSTA on the scientific, technical and socio-economic aspects of impacts of, and vulnerability
and adaptation to, climate change. Consequently, the COP, by its decision 2/CP.11, adopted the “Five-year programme of work
of the Subsidiary Body for Scientific and Technological Advice on impacts, vulnerability and adaptation to climate change”
Finally during COP12 this programme was approved as “Nairobi Work Programme on impacts, vulnerability and adaptation to climate
change”. This programme has fundamental significance not only for developing countries, but also for industrialized nations
in which some sectors of the or social life are particularly vulnerable to climate change, specifically, inter alia EIT countries and new EU Member States. Further development of this adaptation programme economy should contain steps that
provide optimum economic and social effectiveness, risk management, identification of vulnerable sectors and gaps in knowledge,
preparation of a list of policy options, including an analysis of cost effectiveness, selection of the most effective policies,
and a preparedness implementation plan. In Poland the preliminary adaptation programme covered agriculture, water management,
and coastal zone management. For the time being, gaps in knowledge and preparedness measures have been identified. An estimation
of possible impact on these areas was based on chosen GCMs, and sea level rise IPCC scenarios. In conclusion, it was stated
that the results achieved should be seen as a first step forward and a more comprehensive study is necessary to update the
results and cover other sectors of the economy, such as health protection, spatial planning, ecosystems and forestry, and
to develop specific guidelines and recommendations for policy-makers. 相似文献
998.
Biases existing in the lateral boundary conditions (LBCs) influence climate simulations in regional climate models (RCMs). Correcting the biases in global climate model (GCM)-produced LBCs before running RCMs was proposed in previous studies as a possible way to reduce the GCM-related model dependence of future climate projections using RCMs. In this study the ICTP Regional Climate Model Version 4 (RegCM4) is used to investigate the impact of LBC bias correction on projected future changes of regional climate in West Africa. To accomplish this, two types of present versus future simulations are conducted using RegCM4: a control type where both the present and future LBCs are derived directly from the GCM output (as is done in most regional climate downscaling studies); an experiment type where the present-day LBCs are from reanalysis data and future LBCs are derived by combining the reanalysis data and the GCM-projected LBC changes. For each type of simulations, three different sets of LBCs are experimented on: 6-hourly synoptic forcing directly from the reanalysis or GCM, 6-hourly data interpolated from monthly climatology (without diurnal cycle), and 6-hourly data interpolated from the month-specific climatology of diurnal cycles. It is found that the simulations using different LBCs produce similar present-day summer rainfall patterns, but the predicted future changes differ significantly depending on how the LBC bias correction is treated. Specifically, both the bias correction applied at the synoptic scale and the bias correction applied to the monthly interpolated LBCs without diurnal cycle produce a spurious drying signal caused by physical inconsistency in the corrected future LBCs. Interpolated monthly LBCs with diurnal cycle alleviate the problem to a large extent. These results suggest that using bias-corrected LBCs to drive regional climate models may not guarantee reliable future projections although reasonable present climate can be simulated. Physical inconsistencies may be contained in the bias-corrected LBCs, increasing the uncertainties of RCM-produced future projections. 相似文献
999.
Thomas K. Flesch Lowry A. Harper Raymond L. Desjardins Zhiling Gao Brian P. Crenna 《Boundary-Layer Meteorology》2009,132(1):11-30
Inverse-dispersion calculations can be used to infer atmospheric emission rates through a combination of downwind gas concentrations
and dispersion model predictions. With multiple concentration sensors downwind of a compound source (whose component positions
are known) it is possible to calculate the component emissions. With this in mind, a field experiment was conducted to examine
the feasibility of such multi-source inferences, using four synthetic area sources and eight concentration sensors arranged
in different configurations. Multi-source problems tend to be mathematically ill-conditioned, as expressed by the condition
number κ. In our most successful configuration (average κ = 4.2) the total emissions from all sources were deduced to within 10% on average, while component emissions were deduced
to within 50%. In our least successful configuration (average κ = 91) the total emissions were calculated to within only 50%, and component calculations were highly inaccurate. Our study
indicates that the most accurate multi-source inferences will occur if each sensor is influenced by only a single source.
A “progressive” layout is the next best: one sensor is positioned to “see” only one source, the next sensor is placed to see
the first source and another, a third sensor is placed to see the previous two plus a third, and so on. When it is not possible
to isolate any sources κ is large and the accuracy of a multi-source inference is doubtful. 相似文献
1000.
Leena Järvi Ari-Juhani Punkka David M. Schultz Tuukka Petäjä Harri Hohti Janne Rinne Toivo Pohja Markku Kulmala Pertti Hari Timo Vesala 《Boundary-Layer Meteorology》2007,125(2):343-359
On the afternoon of 3 July 2004 in Hyytiälä (Juupajoki, Finland), convective cells produced a strong downburst causing forest damage. The SMEAR II field station, situated near the damage site, enabled a unique micrometeorological analysis of a microburst with differences above and inside the canopy. At the time of the event, a squall line associated with a cold front was crossing Hyytiälä with a reflectivity maximum in the middle of the squall line. A bow echo, rear-inflow notch, and probable mesovortex were observed in radar data. The bow echo moved west-north-west, and its apex travelled just north of Hyytiälä. The turbulence data were analysed at two locations above the forest canopy and at one location at sub-canopy. At 1412 EET (Eastern European Time, UTC+2), the horizontal and vertical wind speed increased and the wind veered, reflecting the arrival of a gust front. At the same time, the carbon dioxide concentration increased due to turbulent mixing, the temperature decreased due to cold air flow from aloft and aerosol particle concentration decreased due to rain scavenging. An increase in the number concentration of ultra-fine particles (< 10 nm) was detected, supporting the new particle formation either from cloud outflow or due to rain. Five minutes after the gust front (1417 EET), strong horizontal and downward vertical wind speed gusts occurred with maxima of 22 and 15 m s?1, respectively, reflecting the microburst. The turbulence spectra before, during and after the event were consistent with traditional turbulence spectral theory. 相似文献