scholarly journals Object-Based Analog Forecasts for Surface Wind Speed

2017 ◽  
Vol 145 (12) ◽  
pp. 5083-5102 ◽  
Author(s):  
Maria E. B. Frediani ◽  
Thomas M. Hopson ◽  
Joshua P. Hacker ◽  
Emmanouil N. Anagnostou ◽  
Luca Delle Monache ◽  
...  
Keyword(s):  
Wind Speed ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Selection Combining ◽  
Random Errors ◽  
Training Set ◽  
Ensemble Forecasts ◽  
Object Based ◽  
Object Area ◽  
Spatial Dimensionality

Analogs are used as a forecast postprocessing technique, in which a statistical forecast is derived from past prognostic states. This study proposes a method to identify analogs through spatial objects, which are then used to create forecast ensembles. The object-analog technique preserves the field’s spatial relationships, reduces spatial dimensionality, and consequently facilitates the use of artificial intelligence algorithms to improve analog selection. Forecast objects are created with a three-step object selection, combining standard image processing algorithms. The resulting objects are used to find similar forecasts in a training set with a similarity measure based on object area intersection and magnitude. Storm-induced power outages in the Northeast United States motivated the method’s validation for 10-m AGL wind speed forecasts. The training set comprises reforecasts and reanalyses of events that caused damages to the utility infrastructure. The corresponding reanalyses of the best reforecast analogs are used to produce the object-analog ensemble forecasts. The forecasts are compared with other analog forecast methods. Analogs representing lower and upper predictability limits provide references to distinguish the method’s ability (to find good analogs) from the training set’s ability (to provide good analogs) to generate skillful ensemble forecasts. The object-analog forecasts are competitively skillful compared to simpler analog techniques with an advantage of lower spatial dimensionality, while generating reliable ensemble forecasts, with reduced systematic and random errors, maintaining correlation, and improving Brier scores.

scholarly journals Evaluation of PBL Parameterizations for Modeling Surface Wind Speed during Storms in the Northeast United States

2016 ◽  
Vol 31 (5) ◽  
pp. 1511-1528 ◽  
Author(s):  
Maria E. B. Frediani ◽  
Joshua P. Hacker ◽  
Emmanouil N. Anagnostou ◽  
Thomas Hopson
Keyword(s):  
United States ◽  
Wind Speed ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Random Errors ◽  
Northeast United States ◽  
Seasonal Characteristics ◽  
Wind Speed Distribution ◽  
Absolute Bias ◽  
Low Speeds

Abstract This study identifies conditions that determine errors in numerical simulations of 10-m wind speed over moderately complex terrain, emphasizing winds that lead to overhead power-line damage over a subregion of the northeast United States. Simulations with the Mellor–Yamada–Janjić (MYJ) scheme, the Yonsei University (YSU) scheme, and a subgrid-scale topographic drag correction (Topo) applied to YSU are used to investigate error components. The wind speed distribution is dominated by low speeds, which are well depicted by Topo, but are underestimated by the MYJ and YSU schemes. Conversely, moderate and high speeds are underestimated by Topo, and MYJ and YSU perform better across specific ranges. Verification samples are conditioned by season, diurnal cycle, topography, and spatial patterns obtained with a clustering analysis. The systematic error is characterized by a positive bias in low speeds, and as speed increases the biases become more negative. Quantile comparisons, along with systematic and random errors, indicate that beyond the dependence on wind speed itself, errors also depend on seasonal characteristics, indirectly defined by scheme stability profiles. The positive relationship between absolute bias and speed originates in the friction velocity parameterization, and the correction for drag in the Topo scheme exacerbates the effect. The Topo scheme adjusts the total bias and sharpens the bias spread but penalizes moderate and high winds. Clusters reveal that in Topo the bias is primarily driven by wind direction. Excessive correction occurs on terrain-interacting flows, and oceanic flow modulates the adjustment, enhancing the scheme’s performance.

Recurrence Characteristics Analysis of Near-Surface Wind Speed Signal with Different Sampling Frequencies

2014 ◽  
Vol 599-601 ◽  
pp. 1605-1609 ◽  
Author(s):  
Ming Zeng ◽  
Zhan Xie Wu ◽  
Qing Hao Meng ◽  
Jing Hai Li ◽  
Shu Gen Ma
Keyword(s):  
Wind Speed ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Recurrence Plot ◽  
Sampling Frequency ◽  
Near Surface ◽  
Gas Leakage ◽  
Time Period ◽  
Characteristics Analysis ◽  
Quantification Analysis

The wind is the main factor to influence the propagation of gas in the atmosphere. Therefore, the wind signal obtained by anemometer will provide us valuable clues for searching gas leakage sources. In this paper, the Recurrence Plot (RP) and Recurrence Quantification Analysis (RQA) are applied to analyze the influence of recurrence characteristics of the wind speed time series under the condition of the same place, the same time period and with the sampling frequency of 1hz, 2hz, 4.2hz, 5hz, 8.3hz, 12.5hz and 16.7hz respectively. Research results show that when the sampling frequency is higher than 5hz, the trends of recurrence nature of different groups are basically unchanged. However, when the sampling frequency is set below 5hz, the original trend of recurrence nature is destroyed, because the recurrence characteristic curves obtained using different sampling frequencies appear cross or overlapping phenomena. The above results indicate that the anemometer will not be able to fully capture the detailed information in wind field when its sampling frequency is lower than 5hz. The recurrence characteristics analysis of the wind speed signals provides an important basis for the optimal selection of anemometer.

Ocean surface wind speed retrieval from C-band quad-polarized SAR measurements at optimal spatial resolution

2020 ◽  
Vol 12 (2) ◽  
pp. 155-164
Author(s):  
He Fang ◽  
William Perrie ◽  
Gaofeng Fan ◽  
Tao Xie ◽  
Jingsong Yang
Keyword(s):  
Wind Speed ◽  
Spatial Resolution ◽  
Surface Wind ◽  
Ocean Surface ◽  
Surface Wind Speed ◽  
Ocean Surface Wind

scholarly journals A Composite View of Surface Signatures and Interior Properties of Nonlinear Internal Waves: Observations and Applications

2008 ◽  
Vol 25 (7) ◽  
pp. 1218-1227 ◽  
Author(s):  
Ming-Huei Chang ◽  
Ren-Chieh Lien ◽  
Yiing Jang Yang ◽  
Tswen Yung Tang ◽  
Joe Wang
Keyword(s):  
Wind Speed ◽  
Surface Waves ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Horizontal Velocity ◽  
Surface Scattering ◽  
Full Width ◽  
Empirical Formulas ◽  
Marine Radar ◽  
Scattering Strength

Abstract Surface signatures and interior properties of large-amplitude nonlinear internal waves (NLIWs) in the South China Sea (SCS) were measured during a period of weak northeast wind (∼2 m s−1) using shipboard marine radar, an acoustic Doppler current profiler (ADCP), a conductivity–temperature–depth (CTD) profiler, and an echo sounder. In the northern SCS, large-amplitude NLIWs propagating principally westward appear at the tidal periodicity, and their magnitudes are modulated at the spring–neap tidal cycle. The surface scattering strength measured by the marine radar is positively correlated with the local wind speed when NLIWs are absent. When NLIWs approach, the surface scattering strength within the convergence zone is enhanced. The sea surface scattering induced by NLIWs is equivalent to that of a ∼6 m s−1 surface wind speed (i.e., 3 times greater than the actual surface wind speed). The horizontal spatial structure of the enhanced sea surface scattering strength predicts the horizontal spatial structure of the NLIW. The observed average half-amplitude full width of NLIWs λη/2 is 1.09 ± 0.2 km; the average half-amplitude full width of the enhanced scattering strength λI/2 is ∼0.57 λη/2. The average half-amplitude full width of the enhanced horizontal velocity convergence of NLIWs λ∂xu/2 is approximately equal to λI/2. The peak of the enhanced surface scattering leads the center of NLIWs by ∼0.46 λη/2. NLIW horizontal velocity convergence is positively correlated with the enhancement of the surface scattering strength. NLIW amplitude is positively correlated with the spatial integration of the enhancement of the surface scattering strength within the convergence zone of NLIWs. Empirical formulas are obtained for estimating the horizontal velocity convergence and the amplitude of NLIWs using radar measurements of surface scattering strength. The enhancement of the scattering strength exhibits strong asymmetry; the scattering strength observed from behind the propagating NLIW is 24% less than that observed ahead, presumably caused by the skewness and the breaking of surface waves induced by NLIWs. Above the center of NLIWs, the surface scattering strength is enhanced slightly, associated with isotropic surface waves presumably induced or modified by NLIWs. This analysis concludes that in low-wind conditions remote sensing measurements may provide useful predictions of horizontal velocity convergences, amplitudes, and spatial structures of NLIWs. Further applications and modification of the presented empirical formulas in different conditions of wind speed, surface waves, and NLIWs or with other remote sensing methods are encouraged.

scholarly journals Deuterium excess in marine water vapor: Dependency on relative humidity and surface wind speed during evaporation

2014 ◽  
Vol 119 (2) ◽  
pp. 584-593 ◽  
Author(s):  
Marion Benetti ◽  
Gilles Reverdin ◽  
Catherine Pierre ◽  
Liliane Merlivat ◽  
Camille Risi ◽  
...  
Keyword(s):  
Water Vapor ◽  
Wind Speed ◽  
Relative Humidity ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Marine Water ◽  
Deuterium Excess
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