Evaluation of the Madden–Julian oscillation in HiRAM          下载免费PDF全文

Jie Jiang  Lu Wang  Jiuwei Zhao  Tim Li 《大气和海洋科学快报》2022,15(4):100194

The aim of this study was to understand the cause of Madden–Julian oscillation (MJO) bias in the High Resolution Atmospheric Model (HiRAM) driven by observed SST through process-oriented diagnosis. Wavenumber-frequency power spectrum and composite analyses indicate that HiRAM underestimates the spectral amplitude over the MJO band and mainly produces non-propagating rather than eastward-propagating intraseasonal rainfall anomalies, as observed. Column-integrated moist static energy (MSE) budget analysis is conducted to understand the MJO propagation bias in the simulation. It is found that the bias is due to the lack of a zonally asymmetric distribution of the MSE tendency anomaly in respect to the MJO convective center, which is mainly attributable to the bias in vertical MSE advection and surface turbulent flux. Further analysis suggests that it is the unrealistic simulation of MJO vertical circulation anomalies in the upper troposphere as well as overestimation of the Rossby wave response that results in the bias.摘要本研究评估了高分辨率大气环流模式HiRAM模拟的MJO. 结果表明, HiRAM模拟的MJO东传很弱. 我们通过计算整层积分的湿静力能 (MSE) 收支来诊断MJO东传模拟偏差的原因. 结果发现, MSE倾向相对于MJO对流中心的纬向非对称分布很弱是导致东传模拟偏弱的原因, 这主要是由MSE垂直平流和地表湍流通量的模拟偏差造成的. 进一步研究表明, 对流层上层MJO垂直环流结构的模拟偏差和MJO对流西侧的Rossby波环流偏强共同导致了模式的偏差. 本研究中指出的MJO传播模拟偏差的原因与之前基于多模式结果的结论不同, 这意味着要想了解特定模式的模拟偏差, 有必要对该模式进行具体分析.  相似文献   

Upper Ocean Temperatures Hit Record High in 2020     

Lijing CHENG  John ABRAHAM  Kevin ETRENBERTH  John FASULLO  Tim BOYER  Ricardo LOCARNINI  Bin ZHANG  Fujiang YU  Liying WAN  Xingrong CHEN  Xiangzhou SONG  Yulong LIU  Michael EMANN  Franco RESEGHETTI  Simona SIMONCELLI  Viktor GOURETSKI  Gengxin CHEN  Alexey MISHONOV  Jim REAGAN  Jiang ZHU 《大气科学进展》2021,38(4):523-530

The long-term warming of the ocean is a critical indicator of both the past and present state of the climate system. It also provides insights about the changes to come, owing to the persistence of both decadal variations and secular trends,which the ocean records extremely well(Hansen et al., 2011;IPCC, 2013;Rhein et al., 2013;Trenberth et al., 2016;Abram et al., 2019).  相似文献   

A mechanism for formation of the western North Pacific monsoon trough: nonlinear upscale cascade     

Qin  Chi  Li  Tim  Liu  Jia  Bi  Mingyu 《Climate Dynamics》2021,56(11):3889-3898

Linear and nonlinear barotropic vorticity model frameworks are constructed to understand the formation of the monsoon trough in boreal summer over the western North Pacific. The governing equation is written with respect to specified zonal background flows, and a wave perturbation is prescribed in the eastern boundary. Whereas a uniform background mean flow leads no scale contraction, a confluent background zonal flow causes the contraction of zonal wavelength. Under linear dynamics, the wave contraction leads to the development of smaller scale vorticity perturbations. As a result, there is no upscale cascade. Under nonlinear dynamics, cyclonic (anticyclonic) wave disturbances shift northward (southward) away from the central latitude due to the vorticity segregation process. The merging of small-scale cyclonic and anticyclonic perturbations finally leads to the generation of a pair of large-scale cyclonic and anti-cyclonic vorticity gyres, straddling across the central latitude. The large-scale cyclonic circulation due to nonlinear upscale cascade can be further strengthened through a positive convection-circulation feedback.

  相似文献   

Airborne Laser-Induced Fluorescence (LIF) Light Detection and Ranging (LiDAR) for the Quantification of Dissolved Organic Matter Concentration in Natural Waters     

Stephanie R. Rogers  Tim Webster  William Livingstone  Nelson J. O’Driscoll 《Estuaries and Coasts》2012,35(4):959-975

Analysis of dissolved organic matter (DOM) concentration and composition is essential to quantifying biological and chemical oxygen demand and atmosphere?Cocean heat flux exchange in natural waters. However, manual water sampling is costly and time consuming over large areas. The purpose of this research was to analyze the applicability of airborne laser-induced fluorescence light detection and ranging (LiDAR) for the detection of DOM in estuarine ecosystems impacted by agriculture. A fluorescence LiDAR system (Airborne Marine) (FLS-AM) was used to assess the DOM concentration of the Annapolis River and Basin, Nova Scotia, Canada, as well as three rivers and their estuaries in Prince Edward Island, Canada. Two FLS-AM flight missions were conducted in the summers of 2008 and 2009 and the resulting datasets were compared with spectral fluorescence signature (SFS DOM) and dissolved organic carbon (DOC) analysis of in situ water samples. Significant positive correlations were found at five of seven sites between the FLS-AM DOM and SFS DOM relationship which indicates that the FLS-AM sensor is a good surrogate for traditional sample collection of DOM data in estuaries in this region. Positive correlations were also found at all sites between FLS-AM DOM values and DOC. FLS-AM DOM patterns show that DOM values are significantly higher in rivers and estuaries that drain watersheds which are heavily impacted by agricultural practices. The results of this study show that the FLS-AM can be used efficiently as a general indicator for how estuaries are affected by runoff from agricultural watersheds in real time and thus reduce the requirement for traditional water sample collection and laboratory analysis methods.  相似文献   

Responding to change: Using scenarios to understand how socioeconomic factors may influence amplifying or dampening exploitation feedbacks among Tanzanian fishers     

Joshua.E. Cinner  Carl. Folke  Tim. Daw  Christina.C. Hicks   《Global Environmental Change》2011,21(1):7-12

Environmental change often requires societies to adapt. In some instances, these adaptations can create feedbacks that amplify the change. Alternatively, other adaptations may dampen the change. We used semi-structured interviews with 240 fishers from nine Tanzanian coastal communities to explore responses to four hypothetical scenarios of increasingly severe declines in their average catch (10%, 20%, 30% and 50%). Overall, a higher proportion of fishers said they would respond to decline using amplifying adaptations (such as fishing harder) than dampening adaptations (such as reducing effort), particularly in the scenarios with lower levels of decline. We used a redundancy analysis to explore whether certain types of responses were related to the fishers’ socioeconomic characteristics. Fishers that would employ amplifying responses had greater economic wealth but lacked options. Fishers who would adopt dampening responses possessed characteristics associated with having livelihood options. Fishers who would adopt neither amplifying nor dampening responses were less likely to belong to community groups and sold the largest proportion of their catch. This study provides novel contributions by differentiating aspects of adaptive capacity that will amplify versus dampen environmental change and by highlighting what the resource users’ themselves say regarding responding to environmental change. Although direct policy application is limited by the study's hypothetical scenario nature, it provides a good beginning to incorporating resource users’ voices into such policy discussions.  相似文献   

Changes of interannual NAO variability in response to greenhouse gases forcing     

Buwen Dong  Rowan T. Sutton  Tim Woollings 《Climate Dynamics》2011,37(7-8):1621-1641

Observations show that there was change in interannual North Atlantic Oscillation (NAO) variability in the mid-1970s. This change was characterized by an eastward shift of the NAO action centres, a poleward shift of zonal wind anomalies and a downstream extension of climate anomalies associated with the NAO. The NAO interannual variability for the period after the mid-1970s has an annular mode structure that penetrates deeply into the stratosphere, indicating a strengthened relationship between the NAO and the Arctic Oscillation (AO) and strengthened stratosphere-troposphere coupling. In this study we have investigated possible causes of these changes in the NAO by carrying out experiments with an atmospheric GCM. The model is forced either by doubling CO₂, or increasing sea surface temperatures (SST), or both. In the case of SST forcing the SST anomaly is derived from a coupled model simulation forced by increasing CO₂. Results indicate that SST and CO₂ change both force a poleward and eastward shift in the pattern of interannual NAO variability and the associated poleward shift of zonal wind anomalies, similar to the observations. The effect of SST change can be understood in terms of mean changes in the troposphere. The direct effect of CO₂ change, in contrast, can not be understood in terms of mean changes in the troposphere. However, there is a significant response in the stratosphere, characterized by a strengthened climatological polar vortex with strongly enhanced interannual variability. In this case, the NAO interannual variability has a strong link with the variability over the North Pacific, as in the annular AO pattern, and is also strongly related to the stratospheric vortex, indicating strengthened stratosphere-troposphere coupling. The similarity of changes in many characteristics of NAO interannual variability between the model response to doubling CO₂ and those in observations in the mid-1970s implies that the increase of greenhouse gas concentration in the atmosphere, and the resulting changes in the stratosphere, might have played an important role in the multidecadal change of interannual NAO variability and its associated climate anomalies during the late twentieth century. The weak change in mean westerlies in the troposphere in response to CO₂ change implies that enhanced and eastward extended mid-latitude westerlies in the troposphere might not be a necessary condition for the poleward and eastward shift of the NAO action centres in the mid-1970s.  相似文献   

Shallow degassing events as a trigger for very-long-period seismicity at Kīlauea Volcano,Hawai‘i     

Matthew Patrick  David Wilson  David Fee  Tim Orr  Don Swanson 《Bulletin of Volcanology》2011,73(9):1179-1186

The first eruptive activity at Kīlauea Volcano’s summit in 25 years began in March 2008 with the opening of a 35-m-wide vent in Halema‘uma‘u crater. The new activity has produced prominent very-long-period (VLP) signals corresponding with two new behaviors: episodic tremor bursts and small explosive events, both of which represent degassing events from the top of the lava column. Previous work has shown that VLP seismicity has long been present at Kīlauea’s summit, and is sourced approximately 1 km below Halema‘uma‘u. By integrating video observations, infrasound and seismic data, we show that the onset of the large VLP signals occurs within several seconds of the onset of the degassing events. This timing indicates that the VLP is caused by forces—sourced at or very near the lava free surface due to degassing—transmitted down the magma column and coupling to the surrounding rock at 1 km depth.  相似文献   

Lava tube shatter rings and their correlation with lava flux increases at Kīlauea Volcano,Hawai‘i     

Tim R. Orr 《Bulletin of Volcanology》2011,73(3):335-346

Shatter rings are circular to elliptical volcanic features, typically tens of meters in diameter, which form over active lava tubes. They are typified by an upraised rim of blocky rubble and a central depression. Prior to this study, shatter rings had not been observed forming, and, thus, were interpreted in many ways. This paper describes the process of formation for shatter rings observed at Kīlauea Volcano during November 2005–July 2006. During this period, tilt data, time-lapse images, and field observations showed that episodic tilt changes at the nearby Pu‘u ‘Ō‘ō cone, the shallow magmatic source reservoir, were directly related to fluctuations in the level of lava in the active lava tube, with periods of deflation at Pu‘u ‘Ō‘ō correlating with increases in the level of the lava stream surface. Increases in lava level are interpreted as increases in lava flux, and were coincident with lava breakouts from shatter rings constructed over the lava tube. The repetitive behavior of the lava flux changes, inferred from the nearly continuous tilt oscillations, suggests that shatter rings form from the repeated rise and fall of a portion of a lava tube roof. The locations of shatter rings along the active lava tube suggest that they form where there is an abrupt decrease in flow velocity through the tube, e.g., large increase in tube width, abrupt decrease in tube slope, and (or) sudden change in tube direction. To conserve volume, this necessitates an abrupt increase in lava stream depth and causes over-pressurization of the tube. More than a hundred shatter rings have been identified on volcanoes on Hawai‘i and Maui, and dozens have been reported from basaltic lava fields in Iceland, Australia, Italy, Samoa, and the mainland United States. A quick study of other basaltic lava fields worldwide, using freely available satellite imagery, suggests that they might be even more common than previously thought. If so, this confirms that episodic fluctuation in lava effusion rate is a relatively common process at basaltic volcanoes, and that the presence of shatter rings in prehistoric lava flow fields can be used as evidence that such fluctuations have occurred.  相似文献