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61.
Atmospheric boundary-layer structure observed during a haze event due to forest-fire smoke 总被引:1,自引:0,他引:1
Markus?PahlowEmail author Jan?Kleissl Marc?B.?Parlange 《Boundary-Layer Meteorology》2005,114(1):53-70
During a haze event in Baltimore, U.S.A. from July 6 to 8, 2002, smoke from forest fires in the Québec region (Canada), degraded air quality and impacted upon local climate, decreasing solar radiation and air temperature. The smoke particles in and above the atmospheric boundary layer (ABL) served as a tracer and provided a unique opportunity to investigate the ABL structure, especially entrainment. Elastic backscatter lidar measurements taken during the haze event distinctly reveal the downward sweeps (or wisps) of smoke-laden air from the free atmosphere into the ABL. Visualisations of mechanisms such as dry convection, the entrainment process, detrainment, coherent entrainment structures, and mixing inside the ABL, are presented. Thermals overshooting at the ABL top are shown to create disturbances in the form of gravity waves in the free atmosphere aloft, as evidenced by a corresponding ripple structure at the bottom of the smoke layer. Lidar data, aerosol ground-based measurements and supporting meteorological data are used to link free atmosphere, mixed-layer and ground-level aerosols. During the peak period of the haze event (July 7, 2002), the correlation between time series of elastic backscatter lidar data within the mixed layer and the scattering coefficient from a nephelometer at ground level was found to be high (R=0.96 for z =324 m, and R=0.89 for z=504 m). Ground-level aerosol concentration was at a maximum about 2 h after the smoke layer intersected with the growing ABL, confirming that the wisps do not initially reach the ground. 相似文献
62.
A fast coupled global climate model (CGCM) is used to study the sensitivity of El Ni?o Southern Oscillation (ENSO) characteristics to a new interactive flux correction scheme. With no flux correction applied our CGCM reveals typical bias in the background state: for instance, the cold tongue in the tropical east Pacific becomes too cold, thus degrading atmospheric sensitivity to variations of sea surface temperature (SST). Sufficient atmospheric sensitivity is essential to ENSO. Our adjustment scheme aims to sustain atmospheric sensitivity by counteracting the SST drift in the model. With reduced bias in the forcing of the atmosphere, the CGCM displays ENSO-type variability that otherwise is absent. The adjustment approach employs a one-way anomaly coupling from the ocean to the atmosphere: heat fluxes seen by the ocean are based on full SST, while heat fluxes seen by the atmosphere are based on anomalies of SST. The latter requires knowledge of the model??s climatological SST field, which is accumulated interactively in the spin-up phase (??training??). Applying the flux correction already during the training period (by utilizing the evolving SST climatology) is necessary for efficiently reducing the bias. The combination of corrected fluxes seen by the atmosphere and uncorrected fluxes seen by the ocean implies a restoring mechanism that counteracts the bias and allows for long stable integrations in our CGCM. A suite of sensitivity runs with varying training periods is utilized to study the effect of different levels of bias in the background state on important ENSO properties. Increased duration of training amplifies the coupled sensitivity in our model and leads to stronger amplitudes and longer periods of the Nino3.4 index, increased emphasis of warm events that is reflected in enhanced skewness, and more pronounced teleconnections in the Pacific. Furthermore, with longer training durations we observe a mode switch of ENSO in our model that closely resembles the observed mode switch related to the mid-1970s ??climate shift??. 相似文献
63.
Kristie?L.?EbiEmail author Jessica?Hartman Nathan?Chan John?Mcconnell Michael?Schlesinger John?Weyant 《Climatic change》2005,73(3):375-393
Climate is one factor that determines the potential range of malaria. As such, climate change may work with or against efforts
to bring malaria under control. We developed a model of future climate suitability for stable Plasmodium falciparum malaria transmission in Zimbabwe. Current climate suitability for stable malaria transmission was based on the MARA/ARMA
model of climatic constraints on the survival and development of the Anopheles vector and the Plasmodium falciparum malaria parasite. We explored potential future geographic distributions of malaria using 16 projections of climate in 2100.
The results suggest that, assuming no future human-imposed constraints on malaria transmission, changes in temperature and
precipitation could alter the geographic distribution of malaria in Zimbabwe, with previously unsuitable areas of dense human
population becoming suitable for transmission. Among all scenarios, the highlands become more suitable for transmission, while
the lowveld and areas with low precipitation show varying degrees of change, depending on climate sensitivity and greenhouse
gas emission stabilization scenarios, and depending on the general circulation model used. The methods employed can be used
within or across other African countries. 相似文献
64.
Anil?KumarEmail author Fei?Chen Dev?Niyogi Joseph?G.?Alfieri Michael?Ek Kenneth?Mitchell 《Boundary-Layer Meteorology》2011,138(2):263-284
Accurately representing complex land-surface processes balancing complexity and realism remains one challenge that the weather
modelling community is facing nowadays. In this study, a photosynthesis-based Gas-exchange Evapotranspiration Model (GEM)
is integrated into the Noah land-surface model replacing the traditional Jarvis scheme for estimating the canopy resistance
and transpiration. Using 18-month simulations from the High Resolution Land Data Assimilation System (HRLDAS), the impact
of the photosynthesis-based approach on the simulated canopy resistance, surface heat fluxes, soil moisture, and soil temperature
over different vegetation types is evaluated using data from the Atmospheric Radiation Measurement (ARM) site, Oklahoma Mesonet,
2002 International H2O Project (IHOP_2002), and three Ameriflux sites. Incorporation of GEM into Noah improves the surface energy fluxes as well
as the associated diurnal cycle of soil moisture and soil temperature during both wet and dry periods. An analysis of midday,
average canopy resistance shows similar day-to-day trends in the model fields as seen in observed patterns. Bias and standard
deviation analyses for soil temperature and surface fluxes show that GEM responds somewhat better than the Jarvis scheme,
mainly because the Jarvis approach relies on a parametrised minimum canopy resistance and meteorological variables such as
air temperature and incident radiation. The analyses suggest that adding a photosynthesis-based transpiration scheme such
as GEM improves the ability of the land-data assimilation system to simulate evaporation and transpiration under a range of
soil and vegetation conditions. 相似文献
65.
The Summer Surface Energy Balance of the High Antarctic Plateau 总被引:1,自引:0,他引:1
Dirk?van?AsEmail author Michiel?van?den?Broeke Carleen?Reijmer Roderik?van?de?Wal 《Boundary-Layer Meteorology》2005,115(2):289-317
The summertime surface energy balance (SEB) at Kohnen station, situated on the high Antarctic plateau (75°00′ S, 0°04′ E,
2892m above sea level) is presented for the period of 8 January to 9 February 2002. Shortwave and longwave radiation fluxes
were measured directly; the former was corrected for problems associated with the cosine response of the instrument. Sensible
and latent heat fluxes were calculated using the bulk method, and eddy-correlation measurements and the modified Bowen ratio
method were used to verify these calculated fluxes. The calculated sub-surface heat flux was checked by comparing calculated
to measured snow temperatures. Uncertainties in the measurements and energy-balance calculations are discussed.
The general meteorological conditions were not extraordinary during the period of the experiment, with a mean 2-m air temperature
of −27.5°C, specific humidity of 0.52×10−3kg kg−1 and wind speed of 4.1ms−1. The experiment covered the transition period from Antarctic summer (positive net radiation) to winter (negative net radiation),
and as a result the period mean net radiation, sensible heat, latent heat and sub-surface heat fluxes were small with values
of −1.1, 0.0, −1.0 and 0.7 Wm−2, respectively. Daily mean net radiation peaked on cloudy days (16 Wm−2) and was negative on clear-sky days (minimum of −19 W m−2). Daily mean sensible heat flux ranged from −8 to +10 Wm−2, latent heat flux from −4 to 0 Wm−2 and sub-surface heat flux from −8 to +7 Wm−2. 相似文献
66.
Recent glacial retreat in High Asia in China and its impact on water resource in Northwest China 总被引:48,自引:0,他引:48
YAO Tandong WANG Youqing LIU Shiying PU Jianchen SHEN Yongping & LU Anxin .Institute of Tibetan Plateau Research Chinese Academy of Sciences Beijing China .Cold Arid Regions Environmental Engineering Research Institute Chinese Academy of Sciences Lanzhou China 《中国科学D辑(英文版)》2004,47(12):1065-1075
There are about 46298 glaciers in the High Asiain China, the total glacial area is about 59406 km , andtotal glacial volume about 5590 km3. These glaciersmainly concentrate around the Himalayas Mountains,Nyainqentanglha Mountains, Kunlun Mountains,Karakoram Mountains and Tianshan Mountains. Theglaciers in the Tibetan Plateau are the major compo-nent of the glaciers in the High Asia in China. Theseglaciers extend north to the arid and desert regions,and become the main water resource in … 相似文献
67.
Influencing domain of peripheral sources in the urban heavy pollution process of Beijing 总被引:1,自引:0,他引:1
Multiple cities in a diveloped economic area may consist of a city cluster,and the difusion and mixing of its pollutants result in the effect of pollutants plume between cities and the large-scale regional pollution diffusion phenomenon.The distant transfer and diffusion of pollutants occurs when massive aerosols are affected by the dynamic porcess of large-scale circulations.Research suggesten that the life span of aerosol particles whose diameters are about 1 um is the longest.The longevity … 相似文献
68.
A 3-D convective cloud model with compressible non-hydrostatic dynamics and the spectral bin microphysics of a 2-D slab-symmetric
model has been used to simulate an observed supercell storm occurring on 29 June, 2000 near Bird City, Kansas, USA. The main
objective of this paper is to study the evolution of particles in this convective storm with bin spectral microphysics scheme.
Graupels form and grow through two mechanisms, deposition and riming, with the riming process dominant on top of the inflow
and in the upper portion of main updraft. Over the outflow and during the developing and mature stages of the storm, graupel
particles mainly grow through deposition with dominant unimodal spectra. Most fall out after growing up. Reducing initial
relative humidity disturbance (increasing initial potential temperature disturbance) has negative impact on the formation
and growth of graupels over the inflow (outflow). This study shows that large graupel and hail could be suppressed by altering
the deposition and coalescence process over the inflow and main updraft. At different locations of the convective cells and
with different initial humidity and potential temperature disturbance, the graupel formation and growth mechanisms are different,
so as to the feasible hail suppression locations and methods.
Supported by National Natural Science Foundation of China (Grant Nos. 40537034, 40805057), and Foundation of Key Laboratory
of Meteorological Disaster of Ministry of Education in Nanjing University of Information Science & Technology (Grant No. KLME060202) 相似文献
69.
Mafic granulite xenoliths have been discovered in many volcanoes (especially alkali basalt and kimberlite) all over the world. They formed generally in lower crust, and recorded lots of in- formation on the lithosphere formation and crust-mantle interacti… 相似文献
70.