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991.
Ho-Jeong Shin Chan Joo Jang Il-Ung Chung 《Asia-Pacific Journal of Atmospheric Sciences》2017,53(4):411-419
Recently we have had abnormal weather events worldwide that are attributed by climate scientists to the global warming induced by human activities. If the global warming continues in the future and such events occur more frequently and someday become normal, we will have an unprecedented climate. This study intends to answer when we will have an unprecedented warm climate, focusing more on the regional characteristics of the timing of unprecedented climate. Using an in-situ observational data from weather stations of annual-mean surface air temperature in Korea from 1973 to 2015, we estimate a timing of unprecedented climate with a linear regression method. Based on the in-situ data with statistically significant warming trends at 95% confidence level, an unprecedented climate in Korea is projected to occur first in Cheongju by 2043 and last in Haenam by 2168. This 125-year gap in the timing indicates that a regional difference in timing of unprecedented climate is considerably large in Korea. Despite the high sensitivity of linear estimation to the data period and resolution, our findings on the large regional difference in timing of unprecedented climate can give an insight into making policies for climate change mitigation and adaptation, not only for the central government but for provincial governments. 相似文献
992.
Qi Zhang Ming Chang Shengzhen Zhou Weihua Chen Xuemei Wang Wenhui Liao Jianing Dai ZhiYong Wu 《Asia-Pacific Journal of Atmospheric Sciences》2017,53(4):519-536
There has been a rapid growth of reactive nitrogen (Nr) deposition over the world in the past decades. The Pearl River Delta region is one of the areas with high loading of nitrogen deposition. But there are still large uncertainties in the study of dry deposition because of its complex processes of physical chemistry and vegetation physiology. At present, the forest canopy parameterization scheme used in WRF-Chem model is a single-layer “big leaf” model, and the simulation of radiation transmission and energy balance in forest canopy is not detailed and accurate. Noah-MP land surface model (Noah-MP) is based on the Noah land surface model (Noah LSM) and has multiple parametric options to simulate the energy, momentum, and material interactions of the vegetation-soil-atmosphere system. Therefore, to investigate the improvement of the simulation results of WRF-Chem on the nitrogen deposition in forest area after coupled with Noah-MP model and to reduce the influence of meteorological simulation biases on the dry deposition velocity simulation, a dry deposition single-point model coupled by Noah- MP and the WRF-Chem dry deposition module (WDDM) was used to simulate the deposition velocity (Vd). The model was driven by the micro-meteorological observation of the Dinghushan Forest Ecosystem Location Station. And a series of numerical experiments were carried out to identify the key processes influencing the calculation of dry deposition velocity, and the effects of various surface physical and plant physiological processes on dry deposition were discussed. The model captured the observed Vd well, but still underestimated the Vd. The self-defect of Wesely scheme applied by WDDM, and the inaccuracy of built-in parameters in WDDM and input data for Noah-MP (e.g. LAI) were the key factors that cause the underestimation of Vd. Therefore, future work is needed to improve model mechanisms and parameterization. 相似文献
993.
Comparison of two drought indices in studying regional meteorological drought events in China 下载免费PDF全文
The composite-drought index (CI), improved weighted average of precipitation index (IWAP), and the objective identification technique for regional extreme events (OITREE) were employed to detect China's regional meteorological drought events (CRMDEs) during 1961–2010. Compared with existing references, CI and IWAP both showed strong ability in identifying CRMDEs. Generally, the results of CI and IWAP were consistent, especially for extreme and severe CRMDEs. During 1961–2010, although the frequencies of extreme and severe CRMDEs based on CI and IWAP both showed weak decreasing trends, the two mean-integrated indices both showed increasing but not significant trends. However, the results of IWAP were more reasonable than CI’s in two aspects. Firstly, the monthly frequency of extreme and severe CRMDEs based on IWAP showed a clear seasonal variation, which coincided with the seasonal variation of the East Asian monsoon over central–eastern China, whereas the frequency based on CI presented a much weaker seasonal variation. Secondly, the two sets of results were sometimes inconsistent with respect to the start and end times of a CRMDE, and CRMDEs based on CI generally showed two unreasonable phenomena: (1) under non-drought conditions, a severe drought stage could suddenly occur in a large area; and (2) during the following period, drought could alleviate gradually in cases of non-precipitation. Comparative analysis suggested that the IWAP drought index possesses obvious advantages in detecting and monitoring regional drought events. 相似文献
994.
Based on combined thresholds of daily maximum and minimum temperatures, a compound heat wave is defined, and then changes in multiple aspects of such heat waves in China are estimated between 1961 and 2015. Our results intriguingly indicate that severe compound heat waves in northern China are characterized by excessively high intensity within short duration, while long duration determines great disaster-causing potential of severe events in the south. In the past few decades, large areas of China have experienced longer, stronger, and more frequent compound heat waves. Northern China has witnessed dramatic intensity increases, with a maximum amplification over 5°C decade–1; while remarkable lengthening in duration has been mostly recorded in the south, with a maximum trend over 1 day decade–1. The spatial extent affected by compound heat waves has significantly expanded since the 1960s, with the largest expanding rate over 6% decade–1 detected in North China and Northeast China. These systematic assessments serve to deepen our understanding of observed changes in compound heat waves across China, and may further shed some light on future adaptations and mitigations against an increasingly warming climate. 相似文献
995.
This study compares the impacts of interannual Arctic sea ice loss and ENSO events on winter haze days in mainland China through observational analyses and AGCM sensitivity experiments. The results suggest that (1) Arctic sea ice loss favors an increase in haze days in central–eastern China; (2) the impact of ENSO is overall contained within southern China, with increased (reduced) haze days during La Niña (El Niño) winters; and (3) the impacts from sea ice loss and ENSO are linearly additive. Mechanistically, Arctic sea ice loss causes quasi-barotropic positive height anomalies over the region from northern Europe to the Ural Mountains (Urals in brief) and weak and negative height anomalies over the region from central Asia to northeastern Asia. The former favors intensified frequency of the blocking over the regions from northern Europe to the Urals, whereas the latter favors an even air pressure distribution over Siberia, Mongolia, and East Asia. This large-scale circulation pattern favors more frequent occurrence of calm and steady weather in northern China and, as a consequence, increased occurrence of haze days. In comparison, La Niña (El Niño) exerts its influence along a tropical pathway by inducing a cyclonic (anticyclonic) lower-tropospheric atmospheric circulation response over the subtropical northwestern Pacific. The northeasterly (southwesterly) anomaly at the northwestern rear of the cyclone (anticyclone) causes reduced (intensified) rainfall over southeastern China, which favors increased (reduced) occurrence of haze days through the rain-washing effect. 相似文献
996.
The higher-order scalar concentration fluctuation properties are examined in the context of Monin–Obukhov similarity theory
for a variety of greenhouse gases that have distinct and separate source/sink locations along an otherwise ideal micrometeorological
field site. Air temperature and concentrations of water vapour, carbon dioxide and methane were measured at high frequency
(10 Hz) above a flat and extensive peat-land soil in the San Joaquin–Sacramento Delta (California, USA) area, subjected to
year-round grazing by beef cattle. Because of the heterogeneous distribution of the sources and sinks of CO2 and especially CH4 emitted by cattle, the scaling behaviour of the higher-order statistical properties diverged from predictions based on a
balance between their production and dissipation rate terms, which can obtained for temperature and H2O during stationary conditions. We identify and label these departures as ‘exogenous’ because they depend on heterogeneities
and non-stationarities induced by boundary conditions on the flow. Spectral analysis revealed that the exogenous effects show
their signatures in regions with frequencies lower than those associated with scalar vertical transport by turbulence, though
the two regions may partially overlap in some cases. Cospectra of vertical fluxes appear less influenced by these exogenous
effects because of the modulating role of the vertical velocity at low frequencies. Finally, under certain conditions, the
presence of such exogenous factors in higher-order scalar fluctuation statistics may be ‘fingerprinted’ by a large storage
term in the mean scalar budget. 相似文献
997.
Koen De Ridder 《Boundary-Layer Meteorology》2010,134(2):257-267
In the roughness sublayer (RSL), Monin–Obukhov surface layer similarity theory fails. This is problematic for atmospheric
modelling applications over domains that include rough terrain such as forests or cities, since in these situations numerical
models often have the lowest model level located within the RSL. Based on empirical RSL profile functions for momentum and
scalar quantities, and scaling the height with the RSL height z
*, we derive a simple bulk transfer relation that accounts for RSL effects. To verify the validity of our approach, these relations
are employed together with wind speed and temperature profiles measured over boreal forest during the BOREAS experimental
campaign to estimate momentum and heat fluxes. It is demonstrated that, when compared with observed flux values, the inclusion
of RSL effects in the transfer relations yields a considerable improvement in the estimated fluxes. 相似文献
998.
Despite their importance for pollutant dispersion in urban areas, the special features of dispersion at street intersections
are rarely taken into account by operational air quality models. Several previous studies have demonstrated the complex flow
patterns that occur at street intersections, even with simple geometry. This study presents results from wind-tunnel experiments
on a reduced scale model of a complex but realistic urban intersection, located in central London. Tracer concentration measurements
were used to derive three-dimensional maps of the concentration field within the intersection. In combination with a previous
study (Carpentieri et al., Boundary-Layer Meteorol 133:277–296, 2009) where the velocity field was measured in the same model,
a methodology for the calculation of the mean tracer flux balance at the intersection was developed and applied. The calculation
highlighted several limitations of current state-of-the-art canyon dispersion models, arising mainly from the complex geometry
of the intersection. Despite its limitations, the proposed methodology could be further developed in order to derive, assess
and implement street intersection dispersion models for complex urban areas. 相似文献
999.
Frequency of Boundary-Layer-Top Fluctuations in Convective and Stable Conditions Using Laser Remote Sensing 总被引:1,自引:0,他引:1
Giovanni Martucci Renaud Matthey Valentin Mitev Hans Richner 《Boundary-Layer Meteorology》2010,135(2):313-331
The planetary boundary-layer (PBL) height is determined with high temporal and altitude resolution from lidar backscatter
profiles. Then, the frequencies of daytime thermal updrafts and downdrafts and of nighttime gravity waves are obtained applying
a fast Fourier transform on the temporal fluctuation of the PBL height. The principal frequency components of each spectrum
are related to the dominant processes occurring at the daytime and nighttime PBL top. Two groups of cases are selected for
the study: one group combines daytime cases, measured in weak horizontal wind conditions and dominated by convection. The
cases show higher updraft and downdraft frequencies for the shallow, convective boundary layer and lower frequencies for a
deep PBL. For cases characterized by strong horizontal winds, the frequencies directly depend on the wind speed. The temporal
variation of the PBL height is determined also in the likely presence of lee waves. For nighttime cases, the main frequency
components in the spectra do not show a real correlation with the nocturnal PBL height. Altitude fluctuations of the top of
the nocturnal boundary layer are observed even though the boundary layer is statically stable. These oscillations are associated
with the wind shear effect and with buoyancy waves at the PBL top. 相似文献
1000.
Ashok K. Luhar 《Boundary-Layer Meteorology》2010,135(2):301-311
Information concerning the average wind speed and the variances of lateral and longitudinal wind velocity fluctuations is
required by dispersion models to characterise turbulence in the atmospheric boundary layer. When the winds are weak, the scalar
average wind speed and the vector average wind speed need to be clearly distinguished and both lateral and longitudinal wind
velocity fluctuations assume equal importance in dispersion calculations. We examine commonly-used methods of estimating these
variances from wind-speed and wind-direction statistics measured separately, for example, by a cup anemometer and a wind vane,
and evaluate the implied relationship between the scalar and vector wind speeds, using measurements taken under low-wind stable
conditions. We highlight several inconsistencies inherent in the existing formulations and show that the widely-used assumption
that the lateral velocity variance is equal to the longitudinal velocity variance is not necessarily true. We derive improved
relations for the two variances, and although data under stable stratification are considered for comparison, our analysis
is applicable more generally. 相似文献