scholarly journals Multiple equilibria and low-frequency variability of wind-driven ocean models

1998 ◽  
Author(s):  
Francois W. Primeau
Keyword(s):  
Multiple Equilibria ◽  
Low Frequency ◽  
Low Frequency Variability ◽  
Ocean Models

scholarly journals Stochastic Subgrid-Scale Ocean Mixing: Impacts on Low-Frequency Variability

2017 ◽  
Vol 30 (13) ◽  
pp. 4997-5019 ◽  
Author(s):  
Stephan Juricke ◽  
Tim N. Palmer ◽  
Laure Zanna
Keyword(s):  
Southern Ocean ◽  
Interannual Variability ◽  
Time Scales ◽  
High Frequency ◽  
Low Frequency ◽  
Global Ocean ◽  
Small Scale ◽  
Subgrid Scale ◽  
Low Frequency Variability ◽  
Ocean Models

In global ocean models, the representation of small-scale, high-frequency processes considerably influences the large-scale oceanic circulation and its low-frequency variability. This study investigates the impact of stochastic perturbation schemes based on three different subgrid-scale parameterizations in multidecadal ocean-only simulations with the ocean model NEMO at 1° resolution. The three parameterizations are an enhanced vertical diffusion scheme for unstable stratification, the Gent–McWilliams (GM) scheme, and a turbulent kinetic energy mixing scheme, all commonly used in state-of-the-art ocean models. The focus here is on changes in interannual variability caused by the comparatively high-frequency stochastic perturbations with subseasonal decorrelation time scales. These perturbations lead to significant improvements in the representation of low-frequency variability in the ocean, with the stochastic GM scheme showing the strongest impact. Interannual variability of the Southern Ocean eddy and Eulerian streamfunctions is increased by an order of magnitude and by 20%, respectively. Interannual sea surface height variability is increased by about 20%–25% as well, especially in the Southern Ocean and in the Kuroshio region, consistent with a strong underestimation of interannual variability in the model when compared to reanalysis and altimetry observations. These results suggest that enhancing subgrid-scale variability in ocean models can improve model variability and potentially its response to forcing on much longer time scales, while also providing an estimate of model uncertainty.

scholarly journals Low-frequency variability in the Gulf of Alaska from coarse and eddy-permitting ocean models

2009 ◽  
Vol 114 (C1) ◽  
Author(s):  
Antonietta Capotondi ◽  
Vincent Combes ◽  
Michael A. Alexander ◽  
Emanuele Di Lorenzo ◽  
Arthur J. Miller
Keyword(s):  
Low Frequency ◽  
Gulf Of Alaska ◽  
Low Frequency Variability ◽  
Ocean Models

scholarly journals Shift Detection in Hydrological Regimes and Pluriannual Low-Frequency Streamflow Forecasting Using the Hidden Markov Model

Water ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 2058 ◽  
Author(s):  
Larissa Rolim ◽  
Francisco de Souza Filho
Keyword(s):  
Time Series ◽  
Markov Model ◽  
Hidden Markov Model ◽  
Extreme Events ◽  
Hidden Markov ◽  
Low Frequency ◽  
Streamflow Forecasting ◽  
Hydrologic Time Series ◽  
Low Frequency Variability ◽  
The Impact

Improved water resource management relies on accurate analyses of the past dynamics of hydrological variables. The presence of low-frequency structures in hydrologic time series is an important feature. It can modify the probability of extreme events occurring in different time scales, which makes the risk associated with extreme events dynamic, changing from one decade to another. This article proposes a methodology capable of dynamically detecting and predicting low-frequency streamflow (16–32 years), which presented significance in the wavelet power spectrum. The Standardized Runoff Index (SRI), the Pruned Exact Linear Time (PELT) algorithm, the breaks for additive seasonal and trend (BFAST) method, and the hidden Markov model (HMM) were used to identify the shifts in low frequency. The HMM was also used to forecast the low frequency. As part of the results, the regime shifts detected by the BFAST approach are not entirely consistent with results from the other methods. A common shift occurs in the mid-1980s and can be attributed to the construction of the reservoir. Climate variability modulates the streamflow low-frequency variability, and anthropogenic activities and climate change can modify this modulation. The identification of shifts reveals the impact of low frequency in the streamflow time series, showing that the low-frequency variability conditions the flows of a given year.

scholarly journals A Chronology of El Niño Events from Primary Documentary Sources in Northern Peru*

2008 ◽  
Vol 21 (9) ◽  
pp. 1948-1962 ◽  
Author(s):  
R. Garcia-Herrera ◽  
D. Barriopedro ◽  
E. Hernández ◽  
H. F. Diaz ◽  
R. R. Garcia ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Primary Sources ◽  
Proxy Data ◽  
Documentary Sources ◽  
Low Frequency Variability ◽  
Northern Peru

Abstract The authors present a chronology of El Niño (EN) events based on documentary records from northern Peru. The chronology, which covers the period 1550–1900, is constructed mainly from primary sources from the city of Trujillo (Peru), the Archivo General de Indias in Seville (Spain), and the Archivo General de la Nación in Lima (Peru), supplemented by a reassessment of documentary evidence included in previously published literature. The archive in Trujillo has never been systematically evaluated for information related to the occurrence of El Niño–Southern Oscillation (ENSO). Abundant rainfall and river discharge correlate well with EN events in the area around Trujillo, which is very dry during most other years. Thus, rain and flooding descriptors, together with reports of failure of the local fishery, are the main indicators of EN occurrence that the authors have searched for in the documents. A total of 59 EN years are identified in this work. This chronology is compared with the two main previous documentary EN chronologies and with ENSO indicators derived from proxy data other than documentary sources. Overall, the seventeenth century appears to be the least active EN period, while the 1620s, 1720s, 1810s, and 1870s are the most active decades. The results herein reveal long-term fluctuations in warm ENSO activity that compare reasonably well with low-frequency variability deduced from other proxy data.

Removing Spurious Low-Frequency Variability in Drifter Velocities

2013 ◽  
Vol 30 (2) ◽  
pp. 353-360 ◽  
Author(s):  
Rick Lumpkin ◽  
Semyon A. Grodsky ◽  
Luca Centurioni ◽  
Marie-Helene Rio ◽  
James A. Carton ◽  
...  
Keyword(s):  
Low Frequency ◽  
Original Data ◽  
Strain Sensors ◽  
Wind Forcing ◽  
Stokes Drift ◽  
Interannual Variations ◽  
Transmission Frequency ◽  
Low Frequency Variability ◽  
Frequency Variations ◽  
Drifting Buoys

Abstract Satellite-tracked drifting buoys of the Global Drifter Program have drogues, centered at 15-m depth, to minimize direct wind forcing and Stokes drift. Drogue presence has historically been determined from submergence or tether strain records. However, recent studies have revealed that a significant fraction of drifters believed to be drogued have actually lost their drogues, a problem that peaked in the mid-2000s before the majority of drifters in the global array switched from submergence to tether strain sensors. In this study, a methodology is applied to the data to automatically reanalyze drogue presence based on anomalous downwind ageostrophic motion. Results indicate that the downwind slip of undrogued drifters is approximately 50% higher than previously believed. The reanalyzed results no longer exhibit the dramatic and spurious interannual variations seen in the original data. These results, along with information from submergence/tether strain and transmission frequency variations, are now being used to conduct a systematic manual reevaluation of drogue presence for each drifter in the post-1992 dataset.

Sign in / Sign up

Export Citation Format

Share Document