三组火山强迫资料差异及其对模式模拟结果的影响

Gao2008、Crowley2013和Sigl2015火山强迫资料,均基于极地冰芯重建.由于每组重建使用的冰芯数据和分析方法等不同,因此结果存在差异,从而影响气候模式应用.文中详细梳理三组火山强迫资料在原始冰芯数据、信号识别提取和沉积通量计算等方面的差异;介绍重建中涉及的对未知火山事件发生季节、纬度及从极地硫酸盐沉积...     

使用ECMWF集合预报数据集估计全球季节平均气候异常的潜在可预报性

利用ECMWF PROVOST项目产生的在给定海表温度强迫下的150(1979～1993)季节集合预报数据集，分析揭示了季节平均气候异常潜在可预报性的全球分布。首先，利用可再现的强迫模态重建集合资料场，在Kolmogorov-Smirnov(K-S)检验的基础上定义潜在可预报性指数PU^k，然后，将重建场的PU^k与重建场贡献于集合平均的方差比结合，提出了定量估计局地潜在可预报性的指数PI。以全球850hPa温度季节平均异常场为例，对PI进行定量计算表明：不仅大部分热带地区，而且热带外一些地区的季节平均气候异常具有潜在可预报性，主要分布在北美、南非和亚洲部分季风区；全球大部分潜在可预报地区主要受ENSO型强迫控制，而部分温带地区如中国华北、中亚、北美南部主要受非ENSO型强迫控制；局地潜在可预报性具有季节性，夏季可预报性较强，冬季较弱。通过与其他几种估计季节潜在可预报性的方法进行比较表明，本文提出的PI方法能更好地把热带外地区受外强迫控制的可预报信号提取出来。     

Evolution and Frontogenesis of an Imbalanced Flow —the Influence of Vapor Distribution and Orographic Forcing

If the initial fields are not in geostrophic balance, the adjustment and evolution will occur in the stratified fluid, and the frontogenesis will occur under suitable conditions. The evolution is studied here with a nonhydrostatic fully compressible meso-scale model (Advanced Regional Prediction System, ARPS). Four cases are designed and compared: (i) control experiment; (ii) with different initial temperature gradient; (iii) with vapor distribution; (iv) with orographic forcing. The results show that: (1) there is an inertial oscillation in the evolution of the imbalanced flow with the frequency of the local Coriolis f, and with its amplitude de-creasing with time. The stationary balanced state can only be approached as it cannot be reached in the limit duration of time, The energy conversion ratio varies in the range of [0, 1 / 3]; (2) the stronger initial tempera-ture gradient can make the final energy conversion ratio higher, and vice versa; (3) suitable vapor distribu-tion is favorable for the frontogenesis. It will bring forward the time of the frontogenesis, strengthen the in-tensity of the cold front, and influence the final energy conversion ratio; (4) the orographic forcing has an ev-idently strengthening effect on the frontogenesis. The strengthening effect on the frontogenesis and the influ-ence on the final energy conversion ratio depend on the relative location of the mountain to the cold front.     

Using the Climate Forecast System Reanalysis as weather input data for watershed models

Obtaining representative meteorological data for watershed‐scale hydrological modelling can be difficult and time consuming. Land‐based weather stations do not always adequately represent the weather occurring over a watershed, because they can be far from the watershed of interest and can have gaps in their data series, or recent data are not available. This study presents a method for using the Climate Forecast System Reanalysis (CFSR) global meteorological dataset to obtain historical weather data and demonstrates the application to modelling five watersheds representing different hydroclimate regimes. CFSR data are available globally for each hour since 1979 at a 38‐km resolution. Results show that utilizing the CFSR precipitation and temperature data to force a watershed model provides stream discharge simulations that are as good as or better than models forced using traditional weather gauging stations, especially when stations are more than 10 km from the watershed. These results further demonstrate that adding CFSR data to the suite of watershed modelling tools provides new opportunities for meeting the challenges of modelling un‐gauged watersheds and advancing real‐time hydrological modelling. Copyright © 2013 John Wiley & Sons, Ltd.     

Phase synchronization of slips by periodical (tangential and normal) mechanical forcing in the spring-slider model

In the present study, the character of slip regimes under weak external periodical (tangential and normal) mechanical forcing has been investigated in a laboratory spring-slider system. We report the experimental evidence of phase synchronization in a slip dynamics, induced by the external periodic mechanical impact. At certain conditions, we have a stick-slip effect in the spring-slider system. To describe this effect, we can use rate-and state-dependent friction law. In our experiments, the slip events are distinguished by acoustic emission bursts, which are generated by slider displacement. In addition to drag, the weak variable mechanical forcing was superimposed either tangential or normal to the slip plane. With increasing external forcing one can see increasing phase synchronization of the first arrivals (onsets) of stick-slip generated acoustic pulses. The grouping of the onsets in a certain phase of the external periodic forcing is considered as a hallmark of the phase synchronization. The onsets of stick-slip pulses in the case of normal mechanical forcing are shifted relative to onsets in the case of tangential forcing.     

An improved diagnostic stratocumulus scheme based on estimated inversion strength and its performance in GAMIL2

Based on satellite data and the estimated inversion strength (EIS) derived by Wood et al. (2006), a feasible and uncomplicated stratocumulus scheme is proposed, referred to as EIS scheme. It improves simulation of cloud radiative forcing (CRF) in the Grid-point Atmospheric Model of IAP/LASG version 2 (GAMIL2.0) model. When compared with the original lower troposphere stability (LTS) scheme, the EIS scheme reproduces more reasonable climatology distributions of clouds and CRF. The parameterization partly corrects CRF underestimation at mid and high latitudes and overestimation in the convective region. Such improvements are achieved by neglecting the effect of free-tropospheric stratification changes that follow a cooler moist adiabat at middle and high latitude, thereby improving simulated cloudiness. The EIS scheme also improves simulation of the CRF interannual variability. The positive net CRF and negative stratiform anomaly in the East Asian and western North Pacific monsoon regions (EAWNPMR) are well simulated. The EIS scheme is more sensitive to sea surface temperature anomalies (SSTA) than the LTS. Therefore, under the effect of a warmer SSTA in the EAWNPMR, the EIS generates a stronger negative stratiform response, which reduces radiative heating in the low and mid troposphere, in turn producing strong subsidence and negative anomalies of both moisture and cloudiness. Consequent decreases in cloud reflection and shading effects ultimately improve simulation of incoming surface shortwave radiative fluxes and CRF. Because of the stronger subsidence, a stronger anomalous anticyclone over the Philippines Sea is simulated by the EIS run, which leads to a better positive precipitation anomaly in eastern China during ENSO winter.     

Multiple time-scale modelling of the circulation in Torres Strait—Australia

Ocean circulation influences nearly all aspects of the marine ecosystem. This study describes the water circulation patterns on time scales from hours to years across Torres Strait and adjacent gulfs and seas, including the north of the Great Barrier Reef. The tridimensional circulation model incorporated realistic atmospheric and oceanographic forcing, including winds, waves, tides, and large-scale regional circulation taken from global model outputs. Simulations covered a hindcast period of 8 years (i.e. 01/03/1997–31/12/2004), allowing the tidal, seasonal, and interannual flow characteristics to be investigated. Results indicated that the most energetic current patterns in Torres Strait were strongly dominated by the barotropic tide and its spring-neap cycle. However, longer-term flow through the strait was mainly controlled by prevailing winds. A dominant westward drift developed in summer over the southeasterly trade winds season, which then weakened and reversed in winter over the northwesterly monsoon winds season. The seasonal flow through Torres Strait was strongly connected to the circulation in the north of the Great Barrier Reef, but showed little connectivity with the coastal circulation in the Gulf of Papua. Interannual variability in Torres Strait was highest during the monsoon period, reflecting variability in wind forcing including the timing of the monsoon. The characteristics of the circulation were also discussed in relation to fine sediment transport. Turbidity level in Torres Strait is expected to peak at the end of the monsoon, while it is likely to be at a low at the end of the trade season, eventually leading to a critically low bottom light level which constitutes a severe risk of seagrass dieback.     

新型地震预警方法研究及预警能力分析

本文研究了一种不同于传统地震预警方法的新型预警方法。这种预警方法利用数据同化技术对实时波动场进行精确估计,然后再利用基于辐射传输理论的蒙特卡洛直接模拟法对波动能量的传播做数值模拟,并最终计算预警目标区烈度并做阈值判断发出预警警报。整个预警过程无需触发、无需定位、无需测定震级、无需利用衰减关系,较传统预警方法具有明显不同的技术手段,比较有效避免了传统地震预警方法中一系列基于经验统计规律的误差累积和单纯依靠初至P波信息在应对复杂地震时的局限性。本文选择了2011年3月11日日本M_w9.0地震和2016年2月6日台湾M_w6.7美浓地震作为预警模拟震例,分析并论证了本文预警方法在处理网外地震、网内地震以及复杂地震时的预警能力,最终得出本文预警方法在应对网内地震时具有良好的预警准确性和时效性,以及相对于传统预警方法在处理复杂地震时具有较大的优势。最后,总结并展望了本文研究工作的不足之处和有待继续研究的地方。     

A Nonlinear Representation of Model Uncertainty in a Convective-Scale Ensemble Prediction System

How to accurately address model uncertainties with consideration of the rapid nonlinear error growth characteristics in a convection-allowing system is a crucial issue for performing convection-scale ensemble forecasts. In this study, a new nonlinear model perturbation technique for convective-scale ensemble forecasts is developed to consider a nonlinear representation of model errors in the Global and Regional Assimilation and Prediction Enhanced System(GRAPES)Convection-Allowing Ensemble Predi...