Sea surface wind stress and drag coefficients: The hexos results

Turbulent fluxes have been measured in the atmospheric surface layer from a boom extending upwind from the Dutch offshore research platform Meetpost Noordwijk (MPN) during HEXMAX (Humidity Exchange over the Sea Main Experiment) in October–November, 1986. We started out to study eddy flux of water vapour, but discrepancies among simultaneous measurements made with three different anemometers led us to develop methods to correct eddy correlation measurements of wind stress for flow distortion by nearby objects. We then found excellent agreement among the corrected wind stress data sets from the three anemometers on the MPN boom and with eddy correlation measurements from a mast on a tripod. Inertial-dissipation techniques gave reliable estimates of wind stress from turbulence spectra, both at MPN and at a nearby ship. The data cover a range of wave ages and the results yield new insights into the variation of sea surface wind stress with sea state; two alternative formulas are given for the nondimensional surface roughness as a function of wave age.     

CGI程序与网站安全性

随着Internet的广泛应用,CGI在现在的互联网应用中也越来越广泛,CGI编程的安全问题也引起越来越多的重视。在此分析了CGI程序运行的中可能存在的漏洞,并提出了相应的简单防御方法。     

The impact of land cover change on the atmospheric circulation

 The NCAR Community Climate Model (version 3), coupled to the Biosphere Atmosphere Transfer scheme and a mixed layer ocean model is used to investigate the impact on the climate of a conservative change from natural to present land cover. Natural vegetation cover was obtained from an ecophysiologically constrained biome model. The current vegetation cover was obtained by perturbing the natural cover from forest to grass over areas where land cover has been observed to change. Simulations were performed for 17 years for each case (results from the last 15 years are presented here). We find that land cover changes, largely constrained to the tropics, SE Asia, North America and Europe, cause statistically significant changes in regional temperature and precipitation but cause no impact on the globally averaged temperature or precipitation. The perturbation in land cover in the tropics and SE Asia teleconnect to higher latitudes by changing the position and strength of key elements of the general circulation (the Hadley and Walker circulations). Many of the areas where statistically significant changes occur are remote from the location of land cover change. Historical land cover change is not typically included in transitory climate simulations, and it may be that the simulation of the patterns of temperature change over the twentieth century by climate models will be further improved by taking it into account. Received: 27 May 1999 / Accepted: July 2000     

The impact of global warming on the Southern Oscillation Index

The Southern Oscillation Index (SOI)??a measure of air pressure difference across the Pacific Ocean, from Tahiti in the south-east to Darwin in the west??is one of the world??s most important climatic indices. The SOI is used to track and predict changes in both the El Ni?o-Southern Oscillation phenomenon, and the Walker Circulation (WC). During El Ni?o, for example, the WC weakens and the SOI tends to be negative. Climatic variations linked to changes in the WC have a profound influence on climate, ecosystems, agriculture, and societies in many parts of the world. Previous research has shown that (1) the WC and the SOI weakened in recent decades and that (2) the WC in climate models tends to weaken in response to elevated atmospheric greenhouse gas concentrations. Here we examine changes in the SOI and air pressure across the Pacific in the observations and in numerous WCRP/CMIP3 climate model integrations for both the 20th and 21st centuries. The difference in mean-sea level air pressure (MSLP) between the eastern and western equatorial Pacific tends to weaken during the 21st century, consistent with previous research. Here we show that this primarily arises because of an increase in MSLP in the west Pacific and not a decline in the east. We also show, in stark contrast to expectations, that the SOI actually tends to increase during the 21st century, not decrease. Under global warming MSLP tends to increase at both Darwin and Tahiti, but tends to rise more at Tahiti than at Darwin. Tahiti lies in an extensive region where MSLP tends to rise in response to global warming. So while the SOI is an excellent indicator of interannual variability in both the equatorial MSLP gradient and the WC, it is a highly misleading indicator of long-term equatorial changes linked to global warming. Our results also indicate that the observed decline in the SOI in recent decades has been driven by natural, internally generated variability. The externally forced signal in the June?CDecember SOI during 2010 is estimated to be approximately 5% of the standard deviation of variability in the SOI during the 20th century. This figure is projected to increase to 40% by the end of the 21st century under the A2 SRES scenario. The 2010 global warming signal is already a major contributor to interdecadal variability in the SOI, equal to 45% of the standard deviation of 30-year running averages of the SOI. This figure is projected to increase to nearly 340% by the end of the 21st century. Implications that these discoveries have for understanding recent climatic change and for seasonal prediction are discussed.     

浅谈气象台站规划及其规划图测绘

气象台站规划必须适应气象业务及其现代化发展需要，同时也应满足职工生活要求 。从这一角度出发，阐明了分析规划时应考虑的因素，制定了台站基本建设规划的思路和方 向，提出了宜采取的办法。     

The impact of shale gas on the costs of climate policy

The use of shale gas is commonly considered as a low-cost option for meeting ambitious climate policy targets. This article explores global and country-specific effects of increasing global shale gas exploitation on the energy markets, on greenhouse gas emissions, and on mitigation costs. The global techno-economic partial equilibrium model POLES (Prospective Outlook on Long-term Energy Systems) is employed to compare policies which limit global warming to 2°C and baseline scenarios when the availability of shale gas is either high or low. According to the simulation results, a high availability of shale gas has rather small effects on the costs of meeting climate targets in the medium and long term. In the long term, a higher availability of shale gas increases baseline emissions of greenhouse gases for most countries and for the world, and leads to higher compliance costs for most, but not all, countries. Allowing for global trading of emission certificates does not alter these general results. In sum, these findings cast doubt on shale gas’s potential as a low-cost option for meeting ambitious global climate targets.

POLICY RELEVANCE

Many countries with a large shale gas resource base consider the expansion of local shale gas extraction as an option to reduce their GHG emissions. The findings in this article imply that a higher availability of shale gas in these countries might actually increase emissions and mitigation costs for these countries and also for the world. An increase in shale gas extraction may spur a switch from coal to gas electricity generation, thus lowering emissions. At the global level and for many countries, though, this effect is more than offset by a crowding out of renewable and nuclear energy carriers, and by lower energy prices, leading to higher emissions and higher mitigation costs in turn. These findings would warrant a re-evaluation of the climate strategy in most countries relying on the exploitation of shale gas to meet their climate targets.     

New Zealand's abandonment of the Carbon Neutral Public Service programme

In 2009, New Zealand's new National-led government abandoned the Carbon Neutral Public Service (CNPS) programme, a Labour-led government initiative intended to help Government achieve carbon neutrality within its core agencies. This short analysis article provides an overview and brief assessment of the CNPS initiative by drawing on the relevant scholarly literature and public documents relating to New Zealand's climate change agenda. It is argued that although the CNPS programme faced a range of challenges it was successful in some respects. Although the Labour-led government was keen to act on climate change mitigation, New Zealand no longer intends to take a lead on carbon neutrality under the National-led government.     

The climatic impact of supervolcanic ash blankets

Supervolcanoes are large caldera systems that can expel vast quantities of ash, volcanic gases in a single eruption, far larger than any recorded in recent history. These super-eruptions have been suggested as possible catalysts for long-term climate change and may be responsible for bottlenecks in human and animal populations. Here, we consider the previously neglected climatic effects of a continent-sized ash deposit with a high albedo and show that a decadal climate forcing is expected. We use a coupled atmosphere-ocean General Circulation Model (GCM) to simulate the effect of an ash blanket from Yellowstone volcano, USA, covering much of North America. Reflectivity measurements of dry volcanic ash show albedo values as high as snow, implying that the effects of an ash blanket would be severe. The modeling results indicate major disturbances to the climate, particularly to oscillatory patterns such as the El Niño Southern Oscillation (ENSO). Atmospheric disruptions would continue for decades after the eruption due to extended ash blanket longevity. The climatic response to an ash blanket is not significant enough to instigate a change to stadial periods at present day boundary conditions, though this is one of several impacts associated with a super-eruption which may induce long-term climatic change.     

太行山东麓一次强对流降雹过程中的地形强迫

利用WRF模式对2011年5月26日发生在太行山东麓的一次强对流降雹过程进行数值模拟,探讨了太行山及周边地形在本次强对流过程的作用。结果表明,控制华北平原的偏东暖湿气流受太行山阻挡并与切变线东南侧的西南暖湿气流汇合,在太行山东侧形成水汽高值区。太行山东坡下垫面向上热通量明显高于华北平原,午后850hPa高度山坡与平原的假相当位温梯度达到0.2 K·km~(-1),850~600 hPa假相当位温垂直梯度达4 K·km~(-1),对应上坡风的垂直速度大于1 m·s~(-1),热力环流为太行山东麓对流的发生提供了动力条件。太行山东侧暖湿气层之上为偏西干冷气流,由此形成的强热力不稳定与水汽高值区、上坡风共同造成太行山东麓强对流过程的发生。局地小尺度地形抬升与重力波共同促使太原盆地有对流单体生成,该单体移经太行山西侧迎风坡受阻挡抬升而增强,越过山顶后与维持在太行山东侧的对流单体发生合并,从而导致对流云的强烈发展。     

太阳辐射日变化对气候模拟的影响

本文用两层大气环流模式,作气候模拟对于太阳辐射日变化的敏感性试验.取实测的七月纬圈平均气候资料作为初始场,积分四十天,对后三十天的结果进行平均,作为模拟的月平均状态.另一个试验则是在模式中去掉太阳辐射的日变化,其它都和第一个试验相同。比较这两个试验的计算结果,发现:若忽略太阳辐射的日变化,(i)使纬圈平均降水和蒸发都减少,尤其在中纬陆地上更为显著;(ii)部分地区土壤湿度减少;(iii)云量增加;(iv)大气顶净辐射收入明显减少;(v)地表净加热明显减少;并使土壤湿度变化不大的地区地表温度明显降低. 我们还取了一月纬圈平均气候资料作为初始场,作了同样的数值试验。得到了类似的结果. 本文的结果表明,要作出正确的气候预测,以及作中、短期降水预报,考虑太阳辐射的日变化都是必要的.     

The impact of high altitude aircraft on the ozone layer in the stratosphere

The paper discusses the potential effects on the ozone layer of gases released by the engines of proposed high altitude supersonic aircraft. The major problem arises from the emissions of nitrogen oxides which have the potential to destroy significant quantities of ozone in the stratosphere. The magnitude of the perturbation is highly dependent on the cruise altitude of the aircraft. Furthermore, the depletion of ozone is substantially reduced when heterogeneous conversion of nitrogen oxides into nitric acid on sulfate aerosol particles is taken into account in the calculation. The sensitivity of the aerosol load on stratospheric ozone is investigated. First, the model indicates that the aerosol load induced by the SO₂ released by aircraft is increased by about 10–20% above the background aerosols at mid-high latitude of the Northern Hemisphere at 15 km for the NASA emission scenario A (the NASA emission scenarios are explained in Tables I to III). This increase in aerosol has small effects on stratospheric ozone. Second, when the aerosol load is increased following a volcanic eruption similar to the eruption of El Chichon (Mexico, April 1982), the ozone column in spring increases by as much as 9% in response to the injection of NO _x from the aircraft with the NASA emission scenario A. Finally, the modeled suggests that significant ozone depletion could result from the formation of additional polar stratospheric clouds produced by the injection of H₂O and HNO₃ by the aircraft engines.     

The impact of soil moisture on dispersion-related characteristics

This study investigates the impact of soil moisture availability on dispersion-related characteristics: surface fric-tion velocity (u*), characteristic scales of temperature and humidity (T* and q*), the planetary boundary layer height (h) and atmospheric stability classified by Monin-Obukhov length (L), Kazanski-Monin parameter (μ) and convective velocity scale (w*) during daytime convective condition using a one-dimensional primitive equation with a refined soil model.     

The impact of the unilateral EU commitment on the stability of international climate agreements

The negotiation strategy of the European Union was analysed with respect to the formation of an international climate agreement for the post-2012 era. Game theory was employed to explore the incentives for key players in the climate policy arena to join future climate agreements. A ?20% unilateral commitment strategy by the EU was compared with a multilateral ?30% emission reduction strategy for all Annex-B countries. Using a numerical integrated assessment climate—economy simulation model, we found that leakage, in the sense of strategic policy reactions on emissions, was negligible. The EU strategy to reduce emissions by 30% (compared with 1990 levels) by 2020, if other Annex-B countries follow suit, does not induce the participation of the USA with a comparable reduction commitment. However, we argue that the original EU proposal can be reshaped so as to stabilize a larger and more ambitious climate coalition than the Kyoto Protocol in its first commitment period.     

The impact of internal atmospheric variability on the North Pacific SST variability

The impact of internal atmospheric variability on North Pacific sea surface temperature (SST) variability is examined based on three coupled general circulation model simulations. The three simulations differ only in the level of atmospheric noise occuring over the ocean at the air-sea interface. The amplitude of atmospheric noise is controlled by use of the interactive ensemble technique. This technique simultaneously couples multiple realizations of a single atmospheric model to a single realization of an ocean model. The atmospheric component models all experience the same SST, but the ocean component is forced by the ensemble averaged fluxes thereby reducing the impact of internal atmospheric dynamics at the air-sea interface. The ensemble averaging is only applied at the air-sea interface so that the internal atmospheric dynamics (i.e., transients) of each atmospheric ensemble member is unaffected. This interactive ensemble technique significantly reduces the SST variance throughout the North Pacific. The reduction in SST variance is proportional to the number of ensemble members indicating that most of the variability can simply be explained as the response to atmospheric stochastic forcing. In addition, the impact of the internal atmospheric dynamics at the air-sea interface masks out much of the tropical-midlatitude SST teleconnections on interannual time scales. Once this interference is reduced (i.e., applying the interactive ensemble technique), tropical-midlatitude SST teleconnections are easily detected.     

The impact of logging on the surrounding flow in a managed forest

The influence of a freshly logged area in a managed pine forest on the flow field is investigated by comparing sodar wind profile data over the forest canopy with the synoptic wind field extracted from North American Regional Reanalysis, National Centers for Environmental Prediction. As a consequence of the pressure gradient arising from the sharp temperature difference between the clearcut and the surrounding uncut forests, the local wind direction over the forest measured with the sodar departs dramatically from the prevailing synoptic wind direction when the latter is transverse to the clearcut-sodar direction. Sodar measurements also indicate systematic strong updrafts during daytime followed by nighttime downdrafts with wind coming from the logged area. This suggests the presence of horizontal advection carrying daytime warm air (or nighttime cool air) from the clearcut to the forested area. This paper also examines the influence of wind velocity, clearcut fetch, and solar radiation on locally generated circulations and advection. The presence of local circulations arising from contrasting neighboring surface characteristics well outside the footprint is of particular relevance for atmospheric flux sites where robust surface?Catmosphere exchange values are sought. This study highlights the high level of circumspection required at the time of identifying locations for flux sites. It also suggests vigilant monitoring of the surrounding landscape during eddy?Cflux measurements particularly in actively managed landscapes.     

The climatic impact of a Sonoran vegetation discontinuity

The international fence separating Mexico and the United States is marked by a sharp vegetation discontinuity in the Sonoran Desert. Due to overgrazing, the Mexican side of the border has shorter grasses, more bare soil, and a higher albedo compared to the adjacent lands in the United States. In this investigation, long-term climate records are analyzed to determine the magnitude of any climatic differences associated with the spatial variation in the vegetation regime. The results suggest that summertime maximum temperatures recorded at the Mexican stations are significantly higher (by nearly 2.5 °C) than the Arizona stations when latitude and elevation are held constant. When only elevation is held constant, the difference in the maximum temperature jumps to approximately 4 dgC. No discernible changes in monthly and/or summer season precipitation could be identified in the records. These findings add support to other site-specific field measurements suggesting warming in desert areas where vegetation cover is decreasing and albedo is increasing.     

The impact of horizontal resolution on moist processes in the ECMWF model

Summer and winter climates simulated with the ECMWF (cycle 33) model at spectral scales T21, T42, T63 and T106 are analyzed to determine the impact of changes in horizontal resolution on atmospheric water vapor, clouds, convection, and precipitation. Qualitative changes in many moist processes occur in the transition from T21 to T42, especially in the tropics; at higher resolutions mostly incremental variations from patterns established at T42 result. Large-scale tropical moist processes are simulated more realistically at T21 than at finer resolutions, possibly reflecting a mismatch between the finer-scale dynamics and the scales at which the underlying assumptions of the physical parameterizations apply. Global precipitation increases monotonically with resolution, as a consequence of increasing convection. Global cloud cover, however, decreases in the transition from T21 to T42 due to drying of the tropics, but then increases slightly at finer resolutions. These small global increases are an outcome of compensating changes in different regions: decreases in cloud cover due to drying of the atmosphere at low latitudes are offset by high-latitude increases resulting from enhanced relative humidity associated with an intensifying atmospheric cold bias at finer resolutions.