检索结果-内蒙古大学图书馆

Experimental Assessment of the Performance of High-Frequency CODAR and WERA Radars to Measure Ocean Currents in Partially Ice-Covered Waters

引用

JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第3期33卷 539-550页

作者： Kamli, Emna Chavanne, Cedric Dumont, Dany Univ Quebec Inst Sci Mer Rimouski 310 Allee UrsulinesCP 3300 Rimouski PQ G5L 3A1 Canada

High-frequency radars (HFRs) measure ocean surface currents remotely through the Bragg scattering of radio waves by surface gravity waves with wavelengths shorter than 50 m. HFR range is affected by sea ice, which dampens surface gravity waves and limits wind fetch for adjacent open waters. HFR range sensitivity to sea ice concentration was empirically determined for two types of HFR-Coastal Ocean Dynamics Applications Radar (CODAR) and Wellen Radar (WERA)-installed on the shores of the lower St. Lawrence estuary, Canada, during winter 2013. One CODAR was operating at 13.5 MHz on the southern shore, and one WERA was operating at 16.15 MHz on the northern shore. Ranges were determined using a signal-to-noise ratio threshold of 6 dB for first-order Bragg scattering measured by the receive antenna elements. Ranges were normalized for expected ranges in ice-free conditions, using empirical relationships determined during summer 2013 between the range and surface gravity wave energy at the Bragg frequencies. Normalized ranges Gamma decrease approximately linearly with increasing sea ice concentration C (averaged over the ice-free observational domain) with a slope close to -1 for both HFR types, that is, Gamma = 1 - C. However, for a given sea ice concentration, range can vary significantly depending on the sea ice spatial distribution.

关键词： Forecasting Geographic location/entity Radars/Radar observations Buoy observations observational techniques and algorithms Sea ice Remote sensing Instrumentation/sensors Hindcasts

来源：评论

学校读者我要写书评

暂无评论

Comparison of Meteorological Radar Signal Detectability with Noncoherent and Spectral-Based Processing

引用

JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第4期33卷 723-739页

作者： Mead, James B. ProSensing Inc 107 Sunderland Rd Amherst MA 01002 USA

Detection of meteorological radar signals is often carried out using power averaging with noise subtraction either in the time domain or the spectral domain. This paper considers the relative signal processing gain of these two methods, showing a clear advantage for spectral-domain processing when normalized spectral width is less than similar to 0.1. A simple expression for the optimal discrete Fourier transform (DFT) length to maximize signal processing gain is presented that depends only on the normalized spectral width and the time-domain weighting function. The relative signal processing gain between noncoherent power averaging and spectral processing is found to depend on a variety of parameters, including the radar wavelength, spectral width, available observation time, and the false alarm rate. Expressions presented for the probability of detection for noncoherent and spectral-based processing also depend on these same parameters. Results of this analysis show that DFT-based processing can provide a substantial advantage in signal processing gain and probability of detection, especially when the normalized spectral width is small and when a large number of samples are available. Noncoherent power estimation can provide superior probability of detection when the normalized spectral width is greater than similar to 0.1, especially when the desired false alarm rate exceeds 10%.

关键词： observational techniques and algorithms Data processing Radars/Radar observations

来源：评论

学校读者我要写书评

暂无评论

Polarimetric Variability of Classic Supercell Storms as a Function of Environment

引用

JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY 2016年第9期55卷 1907-1925页

作者： Van den Broeke, Matthew S. Univ Nebraska Lincoln Dept Earth & Atmospher Sci Lincoln NE USA

Classic supercell storms occur in a generally well understood environment characterized by instability and vertical wind shear. Within this broadly favorable environment, large day-to-day variability in environmental parameters may lead to widely varying radar presentation of storms. Of interest here is whether specific storm structures exhibit repeatable characteristics in similar environments and whether radar presentation can be predicted with knowledge of environmental characteristics. Specifically, this paper focuses on (i) updraft characteristics inferred using differential reflectivity ZDR columns, (ii) characteristics of storm-relative inflow inferred using ZDR arcs, and (iii) areal extent and cyclicality of polarimetrically inferred hailfall at low levels. Variability of these radar features is compared among storms in similar environments and among a larger subset of storms across highly varying environments. The similarity of storms in similar and different environments is quantified, and tornadic and nontornadic storms are compared. Associations between inferred updraft, inflow, and hailfall characteristics and environmental variables are discussed. Storm features generally exhibit greater similarity among storms in similar environments than across environments, although exceptions occur. The results indicate that many radar features of classic supercells may be useful to learn about microphysical variability across environments.

关键词： Atm/Ocean Structure/ Phenomena Supercells observational techniques and algorithms Radars/Radar observations Forecasting Nowcasting

来源：评论

学校读者我要写书评

暂无评论

Global Comparisons of Regional Life Cycle Properties and Motion of Multiday Convective Systems: Tropical and Midlatitude Land and Ocean

引用

JOURNAL OF CLIMATE 2016年第16期29卷 5837-5858页

作者： Vant-Hull, Brian Rossow, William Pearl, Cindy CUNY City Coll NOAA Cooperat Remote Sensing & Technol Inst New York NY 10031 USA CUNY City Coll Remote Sensing Climate Grp NOAA Cooperat Remote Sensing & Technol Ctr New York NY 10031 USA

Tracking of convective cloud systems (cloud-top temperature <245 K) in geosynchronous satellite images at 3-h intervals is used to determine life cycle statistics of convective systems in four regimes: tropical land and ocean and midlatitude land and ocean, including seasonal comparisons. The ISCCP tracking dataset covers the period 1984-2006. Only systems with lifetimes greater than or equal to 1 day that were moving predominantly eastward or westward are considered, with splits and merges combined into larger extended convective systems. The life cycle variables are lifetime (duration), maximum area, and minimum cloud-top temperature. These are compared to each other and to the speed of longitudinal motion. Distributions and relationships between the life cycle variables are similar to previous studies based on single-day lifetimes, but the current study is globally extensive (all longitudes at lower and middle latitudes) and multidecadal, which allows extension of such results to rarer, larger, and longer-lived convective systems than previous work. Velocity distributions were monomodal with tails skewed in the direction of the zonal mean wind, being almost purely eastward in the midlatitudes but nearly symmetric in both directions with a small westward bias in the tropics. Representative life cycles for each geographical region are formed by averaging together systems with similar lifetimes. These composite life cycles show that, except for the first and last days, the daily evolution of most system variables exhibits little variation during the average multiday convective life cycle, although the cloud area goes through one cycle of expansion and contraction in a lifetime.

关键词： Circulation/ Dynamics Clouds Large-scale motions Madden-Julian oscillation Mesoscale systems Physical Meteorology and Climatology Climatology observational techniques and algorithms Satellite observations

来源：评论

学校读者我要写书评

暂无评论

Synthetic Modeling for an Acoustic Exploration System for Physical Oceanography

引用

JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第1期33卷 191-200页

作者： Biescas, Berta Ruddick, Barry Kormann, Jean Sallares, Valenti Nedimovic, Mladen R. Carniel, Sandro CNR Ist Sci Marine Via Gobetti 101 I-40129 Bologna Italy Dalhousie Univ Dept Oceanog Halifax NS Canada Barcelona Supercomp Ctr Barcelona Spain Inst Marine Sci Dept Marine Geosci Barcelona Spain Dalhousie Univ Dept Earth Sci Halifax NS Canada CNR Ist Sci Marine Venice Italy

Marine multichannel seismic (MCS) data, used to obtain structural reflection images of the earth's subsurface, can also be used in physical oceanography exploration. This method provides vertical and lateral resolutions of O(10-100) m, covering the existing observational gap in oceanic exploration. All MCS data used so far in physical oceanography studies have been acquired using conventional seismic instrumentation originally designed for geological exploration. This work presents the proof of concept of an alternative MCS system that is better adapted to physical oceanography and has two goals: 1) to have an environmentally low-impact acoustic source to minimize any potential disturbance to marine life and 2) to be light and portable, thus being installed on midsize oceanographic vessels. The synthetic experiments simulate the main variables of the source, shooting, and streamer involved in the MCS technique. The proposed system utilizes a 5-s-long exponential chirp source of 208 dB relative to 1 mu Pa at 1m with a frequency content of 20-100 Hz and a relatively short 500-m-long streamer with 100 channels. This study exemplifies through numerical simulations that the 5-s-long chirp source can reduce the peak of the pressure signal by 26 dB with respect to equivalent air gun-based sources by spreading the energy in time, greatly reducing the impact to marine life. Additionally, the proposed system could be transported and installed in midsize oceanographic vessels, opening new horizons in acoustic oceanography research.

关键词： observational techniques and algorithms Acoustic measurements/effects In situ oceanic observations

来源：评论

学校读者我要写书评

暂无评论

Extreme Low-Level Updrafts and Wind Speeds Measured by Dropsondes in Tropical Cyclones

引用

MONTHLY WEATHER REVIEW 2016年第6期144卷 2177-2204页

作者： Stern, Daniel P. Bryan, George H. Aberson, Sim D. Natl Ctr Atmospher Res POB 3000 Boulder CO 80307 USA NOAA AOML Hurricane Res Div Miami FL USA

Previous studies have found surprisingly strong vertical motions in low levels of some tropical cyclones. In this study, all available dropsondes (similar to 12 000) within tropical cyclones during 1997-2013 are examined, in order to create a dataset of the most extreme updrafts (>= 10m s(-1);169 sondes) and wind speeds (>= 90m s(-1);64 sondes). It is shown that extreme low-level (0-3 km) updrafts are ubiquitous within intense (category 4 and 5) tropical cyclones, and that few such updrafts have been observed within weaker storms. These extreme updrafts, which are almost exclusively found within the eyewall just inward of the radius of maximum winds, sometimes occur in close association with extreme horizontal wind speeds. Consistent with previous studies, it is suggested that both the extremes in vertical velocity and wind speed are associated with small-scale (;1 km) vortices that exist along the eye-eyewall interface. As a substantial number of updrafts are found within a kilometer of the surface, it can be shown that it is implausible for buoyancy to be the primary mechanism for vertical acceleration. Additionally, the azimuthal distribution of both the extreme updrafts and wind speeds is strongly associated with the orientation of the environmental vertical wind shear.

关键词： Circulation/ Dynamics Buoyancy Updrafts Atm/Ocean Structure/ Phenomena Extreme events Tropical cyclones Wind gusts observational techniques and algorithms Dropsondes

来源：评论

学校读者我要写书评

暂无评论

Estimating Turbulent Dissipation from Microstructure Shear Measurements Using Maximum Likelihood Spectral Fitting over the Inertial and Viscous Subranges

引用

JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第4期33卷 713-722页

作者： Bluteau, Cynthia E. Jones, Nicole L. Ivey, Gregory N. Univ Western Australia Sch Civil Environm & Min Engn MO1535 Stirling Highway Perth WA 6009 Australia Univ Western Australia Oceans Inst Perth WA 6009 Australia

A technique is presented to derive the dissipation of turbulent kinetic energy epsilon by using the maximum likelihood estimator (MLE) to fit a theoretical or known empirical model to turbulence shear spectral observations. The commonly used integration method relies on integrating the shear spectra in the viscous range, thus requiring the resolution of the highest wavenumbers of the turbulence shear spectrum. With current technology, the viscous range is not resolved at sufficiently large wavenumbers to estimate high epsilon;however, long inertial subranges can be resolved, making spectral fitting over both this subrange and the resolved portion of the viscous range an attractive method for deriving e. The MLE takes into account the chi-distributed properties of the spectral observations, and so it does not rely on the log-transformed spectral observations. This fitting technique can thus take advantage of both the inertial and viscous subranges, a portion of both, or simply one of the subranges. This flexibility allows a broad range of epsilon to be resolved. The estimated 6 is insensitive to the range of wavenumbers fitted with the model, provided the noise-dominated portion of the spectra and the low wavenumbers impacted by the mean flow are avoided. For epsilon less than or similar to 10(-6) W kg(-1), the MLE fitting estimates agree with those obtained by integrating the spectral observations. However, with increasing epsilon the viscous subrange is not fully resolved and the integration method progressively starts to underestimate epsilon compared with the values obtained from fitting the spectral observations.

关键词： Applications Circulation/ Dynamics Field experiments In situ oceanic observations Mathematical and statistical techniques Mixing observational techniques and algorithms Spectral analysis/models/distribution Time series Turbulence

来源：评论

学校读者我要写书评

暂无评论

The Construction of a Three-Dimensional Antenna Gain Matrix and Its Impact on Retrieving Sea Surface Mean Square Slope Based on Aircraft Wave Spectrometer Data

引用

JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第4期33卷 847-856页

作者： Li, Xiuzhong He, Yijun Zhang, Biao Fan, Chenqing Nanjing Univ Informat Sci & Technol Sch Marine Sci 219 Ningliu Rd Nanjing 210044 Jiangsu Peoples R China State Ocean Adm Inst Oceanog 1 Qingdao Peoples R China

In this study, a rotating frequency-modulated continuous wave (FMCW) radar is installed on an aircraft to retrieve the sea wave spectra. Because the aircraft attitude angles produce the incorrect antenna gain used in the radar equation, the incorrect normalized radar cross section (NRCS) of the sea surface will be acquired. To eliminate the effect of the angles, a three-dimensional matrix of the radar antenna gain is constructed by means of coordinate transformation and interpolation, based on a large set of configurations of the aircraft attitude angles (roll, pitch, etc.). With the application of the matrix, the NRCS of the sea surface is corrected and the calculating time is reduced. Then the sea surface mean square slope (MSS) is obtained from the echoes of the airborne wave spectrometer. Considering a weak periodicity of MSS due to low sea state, four images are presented to show the variation of the MSS after aircraft attitude angle correction. The results indicate that the accurate incidence angle of the antenna beam center is critical for retrieving the sea surface MSS, and that the magnitude of the MSS from three cycles of radar echoes can be changed by as much as 40% within 5 degrees of the attitude angles. Furthermore, the MSS becomes more periodic and regular after correction.

关键词： Aircraft observations Atm/Ocean Structure/ Phenomena Data processing observational techniques and algorithms Radars/Radar observations Remote sensing Sea state

来源：评论

学校读者我要写书评

暂无评论

Observations of the Structure and Evolution of Hurricane Edouard (2014) during Intensity Change. Part II: Kinematic Structure and the Distribution of Deep Convection

引用

MONTHLY WEATHER REVIEW 2016年第9期144卷 3355-3376页

作者： Rogers, Robert F. Zhang, Jun A. Zawislak, Jonathan Jiang, Haiyan Alvey, George R., III Zipser, Edward J. Stevenson, Stephanie N. NOAA Atlantic Oceanog & Meteorol Lab Hurricane Res Div Miami FL 33149 USA Univ Miami Rosenstiel Sch Marine & Atmospher Sci Cooperat Inst Marine & Atmospher Studies 4600 Rickenbacker Causeway Miami FL 33149 USA Florida Int Univ Miami FL 33199 USA Univ Utah Salt Lake City UT USA SUNY Albany Albany NY 12222 USA

The structural evolution of the inner core and near-environment throughout the life cycle of Hurricane Edouard (2014) is examined using a synthesis of airborne and satellite measurements. This study specifically focuses on differences in the distribution of deep convection during two periods: when Edouard intensified toward hurricane status, and when Edouard peaked in intensity and began to weaken. While both periods saw precipitation maximized in the downshear-left and upshear-left quadrants, deep convection was only seen from the aircraft during the intensifying period. Deep convection was located farther inside the radius of maximum winds (RMW) during the intensifying period than the weakening period. This convection is traced to strong updrafts inside the RMW in the downshear-right quadrant, tied to strong low-level convergence and high convective available potential energy (CAPE) as the storm remained over warm water in a moist environment. Strong updrafts persisted upshear left and were collocated with high inertial stability in the inner core. During weakening, no deep convection was present, and the precipitation that was observed was associated with weaker convergence downshear right at larger radii, as CAPE was reduced from lower sea surface temperatures, reduced humidity from subsidence, and a stronger warm core. Weak updrafts were seen upshear left, with little coincidence with the high inertial stability of the inner core. These results highlight the importance of the azimuthal coverage of precipitation and the radial location of deep convection for intensification. A more symmetrical coverage can occur despite the presence of shear driven azimuthal asymmetries in both the forcing and the local environment of the precipitation.

关键词： Atm/Ocean Structure/ Phenomena Convective clouds Hurricanes/typhoons observational techniques and algorithms Aircraft observations

来源：评论

学校读者我要写书评

暂无评论

The Warm-Core Structure of Hurricane Earl (2010)

引用

JOURNAL OF THE ATMOSPHERIC SCIENCES 2016年第8期73卷 3305-3328页

作者： Stern, Daniel P. Zhang, Fuqing Univ Corp Atmospher Res 7 Grace Hopper Ave Monterey CA 93943 USA Penn State Univ Dept Meteorol 503 Walker Bldg University Pk PA 16802 USA

The warm-core structure of Hurricane Earl (2010) is examined on four different days, spanning periods of both rapid intensification (RI) and weakening, using high-altitude dropsondes from both the inner core and the environment, as well as a convection-permitting numerical forecast. During RI, strong warming occurred at all heights, while during rapid weakening, little temperature change was observed, implying the likelihood of substantial (unobserved) cooling above flight level (12 km). Using a local environmental reference state yields a perturbation temperature profile with two distinct maxima of approximately equal magnitude: one at 4-6-km and the other at 9-12-km height. However, using a climatological-mean sounding instead results in the upper-level maximum being substantially stronger than the midlevel maximum. This difference results from the fact that the local environment of Earl was warmer than the climatological mean and that this relative warmth increased with height. There is no obvious systematic relationship between the height of the warm core and either intensity or intensity change for either reference state. The structure of the warm core simulated by the convection-permitting forecast compares well with the observations for the periods encompassing RI. Later, an eyewall replacement cycle went unforecast, and increased errors in the warm-core structure are likely related to errors in the forecast wind structure. At most times, the simulated radius of maximum winds (RMW) had too great of an outward slope (the upper-level RMW was too large), and this is likely also associated with structural biases in the warm core.

关键词： Atm/Ocean Structure/ Phenomena Tropical cyclones Physical Meteorology and Climatology Temperature observational techniques and algorithms Dropsondes Radars/Radar observations Forecasting Numerical weather prediction/forecasting

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：