Characteristics and evolution of a coastal mesoscale eddy in the Western Bay of Bengal monitored by high-frequency radars     

《Dynamics of Atmospheres and Oceans》2019

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Equatorward shift of the South Asian high in response to anthropogenic forcing   总被引：1，自引：0，他引：1  

Xia Qu  Gang Huang  Kaiming Hu  Shang-Ping Xie  Yan Du  Xiao-Tong Zheng  Lin Liu 《Theoretical and Applied Climatology》2015,119(1-2):113-122

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Accurate polynomial expressions for the density and specific volume of seawater using the TEOS-10 standard     

《Ocean Modelling》2015

A new set of approximations to the standard TEOS-10 equation of state are presented. These follow a polynomial form, making it computationally efficient for use in numerical ocean models. Two versions are provided, the first being a fit of density for Boussinesq ocean models, and the second fitting specific volume which is more suitable for compressible models. Both versions are given as the sum of a vertical reference profile (6th-order polynomial) and an anomaly (52-term polynomial, cubic in pressure), with relative errors of ∼0.1% on the thermal expansion coefficients. A 75-term polynomial expression is also presented for computing specific volume, with a better accuracy than the existing TEOS-10 48-term rational approximation, especially regarding the sound speed, and it is suggested that this expression represents a valuable approximation of the TEOS-10 equation of state for hydrographic data analysis. In the last section, practical aspects about the implementation of TEOS-10 in ocean models are discussed.  相似文献   

Density currents in the two-layer flow: an example of Dardanelles outflow     

《Oceanologica Acta》2003,26(3):243-253

Observations from hydrographic surveys are used to describe the density current flowing through the Dardanelles strait into the Marmara Sea. Aegean water plunges below the surface and flows into the Marmara Sea. This flow joins into the Marmara Sea as a negatively buoyant plume and sinks through the deeper parts. Seasonal variation in the incoming water density results in the observing mainly two different forms of the density current in this area. These two forms are boundary currents and intrusion. Boundary currents were observed as a dense bottom current during the winter when the inflowing water density attains to annual maxima and as an overflow during the autumn when the inflowing water density drops to annual minimum. Intrusion form of the density current was observed during the summer.  相似文献   

Assessing 4D-VAR for dynamical mapping of coastal high-frequency radar in San Diego     

《Dynamics of Atmospheres and Oceans》2010,49(1-3):175-197

The problem of dynamically mapping high-frequency (HF) radar radial velocity observations is investigated using a three-dimensional hydrodynamic model of the San Diego coastal region and an adjoint-based assimilation method. The HF radar provides near-real-time radial velocities from three sites covering the region offshore of San Diego Bay. The hydrodynamical model is the Massachusetts Institute of Technology general circulation model (MITgcm) with 1 km horizontal resolution and 40 vertical layers. The domain is centered on Point Loma, extending 117 km offshore and 120 km alongshore. The reference run (before adjustment) is initialized from a single profile of T and S and is forced with wind data from a single shore station and with zero heat and fresh water fluxes. The adjoint of the model is used to adjust initial temperature, salinity, and velocity, hourly temperature, salinity and horizontal velocities at the open boundaries, and hourly surface fluxes of momentum, heat and freshwater so that the model reproduces hourly HF radar radial velocity observations. Results from a small number of experiments suggest that the adjoint method can be successfully used over 10-day windows at coastal model resolution. It produces a dynamically consistent model run that fits HF radar data with errors near the specified uncertainties. In a test of the forecasting capability of the San Diego model after adjustment, the forecast skill was shown to exceed persistence for up to 20 h.  相似文献   

Influence of Sea Surface Temperature on the Predictability of Idealized Tropical Cyclone Intensity     

钟权加  李建平  李舒文  王羱  丁瑞强  张立凤 《热带气象学报(英文版)》2021,27(4):355-367

The role of sea surface temperature (SST) forcing in the development and predictability of tropical cyclone (TC) intensity is examined using a large set of idealized numerical experiments in the Weather Research and Forecasting (WRF) model. The results indicate that the onset time of rapid intensification of TC gradually decreases, and the peak intensity of TC gradually increases, with the increased magnitude of SST. The predictability limits of the maximum 10 m wind speed (MWS) and minimum sea level pressure (MSLP) are ~72 and ~84 hours, respectively. Comparisons of the analyses of variance for different simulation time confirm that the MWS and MSLP have strong signal-to-noise ratios (SNR) from 0-72 hours and a marked decrease beyond 72 hours. For the horizontal and vertical structures of wind speed, noticeable decreases in the magnitude of SNR can be seen as the simulation time increases, similar to that of the SLP or perturbation pressure. These results indicate that the SST as an external forcing signal plays an important role in TC intensity for up to 72 hours, and it is significantly weakened if the simulation time exceeds the predictability limits of TC intensity.  相似文献   

Sheared turbulence in a weakly stratified upper ocean     

《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(2):387-407

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Evaluation of ENVISAT ASAR data for sea surface wind retrieval in Hong Kong coastal waters of China   总被引：2，自引：1，他引：1  

XU Qing  LIN Hui  ZHENG Quanan  XIU Peng  CHENG Yongcun  LIU Yuguang 《海洋学报(英文版)》2008,27(4):57-62

The C-band wind speed retrieval models, CMOD4, CMOD - IFR2, and CMOD5 were applied to retrieval of sea surface wind speeds from ENVISAT （European environmental satellite） ASAR （advanced synthetic aperture radar） data in the coastal waters near Hong Kong during a period from October 2005 to July 2007. The retrieved wind speeds are evaluated by comparing with buoy measurements and the QuikSCAT （quick scatterometer） wind products. The results show that the CMOD4 model gives the best performance at wind speeds lower than 15 m/s. The correlation coefficients with buoy and QuikSCAT winds are 0.781 and 0.896, respectively. The root mean square errors are the same 1.74 m/s. Namely, the CMOD4 model is the best one for sea surface wind speed retrieval from ASAR data in the coastal waters near Hong Kong.  相似文献   

Low latitude storm time ionospheric electrodynamics     

《Journal of Atmospheric and Solar》2002,64(12-14):1401-1408

The response of the low latitude ionosphere to high latitude convection has long been the subject of considerable interest. Radar, ionosonde, magnetometer, and satellite measurements have been extensively used for studying the time-dependent characteristics of low-latitude disturbance electric fields and currents, and their coupling to the high latitude convection. Several global convection models have been used to explore the relationship between inner magnetospheric processes, and mid- and low-latitude ionospheric electrodynamic effects during geomagnetically active times. Recently, significant progress has been made in quantifying the average storm time-dependent responses of low latitude electrodynamic plasma drifts and currents to changes in the high latitude convection, and in the validation of global convection and ionospheric disturbance models. However, there are several fundamental questions dealing mostly with the large variability of the disturbance electric fields. In this review, we examine the latest progress in these studies and discuss a number of outstanding problems.  相似文献   

A role for nitrite in the production of nitrous oxide in the lower euphotic zone of the oligotrophic North Pacific Ocean     

《Deep Sea Research Part I: Oceanographic Research Papers》2014

Understanding the role of the oceans in the Earth's changing climate requires comprehension of the relevant metabolic pathways which produce climatically important trace gases. The global ocean represents one of the largest natural sources of nitrous oxide (N₂O) that is produced by selected archaea and/or bacteria during nitrogen (N) metabolism. In this study, the role of nitrite (NO₂⁻) in the production of N₂O in the upper water column of the oligotrophic North Pacific Subtropical Gyre was investigated, focusing primarily on the lower euphotic zone where NO₂⁻ concentrations at the primary NO₂⁻ maximum reached 195 nmol L⁻¹. Free-drifting sediment trap arrays were deployed to measure N cycle processes in sinking particulate material and the addition of selected N substrates to unpreserved sediment traps provided an experimental framework to test hypotheses regarding N₂O production pathways and controls. Sinking particles collected using NO₂⁻-amended, unpreserved sediment traps exhibited significant production of N₂O at depths between 100 and 200 m. Subsequent stable isotope tracer measurements conducted on sediment trap material amended with ¹⁵NO₂⁻ yielded elevated δ¹⁵N values of N₂O, supporting N₂O production via a NO₂⁻ metabolism pathway. Experiments on seawater collected from 150 m showed N₂O production via NO₂⁻ metabolism also occurs in the water-column and indicated that the concentration of NO₂⁻ relative to NH₄⁺ availability may be an important control. These findings provide evidence for the production of N₂O via nitrifer-denitrification in the lower euphotic zone of the open ocean, whereby NO₂⁻ is reduced to N₂O by ammonia-oxidizing microorganisms.  相似文献