scholarly journals Temporal Filtering Enhances the Skewness of Sea Surface Winds

2018 ◽  
Vol 31 (14) ◽  
pp. 5695-5706 ◽  
Author(s):  
Adam H. Monahan
Keyword(s):  
Time Scales ◽  
Surface Wind ◽  
Cutoff Frequency ◽  
Sea Surface ◽  
Generic Model ◽  
Wind Component ◽  
Surface Winds ◽  
Near Surface ◽  
Non Gaussian ◽  
Equatorial Band

The component of the sea surface wind in the along-mean wind direction is known to display pronounced skewness at many locations over the ocean. A recent study by Proistosescu et al. found that the skewness of daily 850-hPa air temperature measured by radiosondes is typically reduced by bandpass filtering. This behavior was also shown to be characteristic of correlated additive–multiplicative (CAM) noise, which has been proposed as a generic model for non-Gaussian variability in the atmosphere and ocean. The present study shows that if the cutoff frequency is not too low, the skewness of the along-mean wind component is enhanced by low-pass filtering, particularly in the equatorial band and in the midlatitude storm tracks. The filter time scale beyond which skewness is systematically reduced by filtering is of the daily to synoptic scale, except in a narrow equatorial band where it is of subseasonal to seasonal time scales. This behavior is reproduced in an idealized stochastic model of the near-surface winds, in which key parameters are the characteristic time scales of the nonlinear dynamics and of the noise. These results point toward more general approaches for assessing the relative importance of multiplicative noise or dynamical nonlinearities in producing non-Gaussian structure in atmospheric and oceanic fields.

scholarly journals Effects of sea surface winds on marine aerosols characteristics and impacts on longwave radiative forcing over the Arabian Sea

2008 ◽  
Vol 8 (4) ◽  
pp. 15855-15899 ◽  
Author(s):  
Vijayakumar S. Nair ◽  
S. Suresh Babu ◽  
S. K. Satheesh ◽  
K. Krishna Moorthy
Keyword(s):  
Wind Speed ◽  
Radiative Forcing ◽  
Arabian Sea ◽  
Near Infrared ◽  
Surface Wind ◽  
Sea Surface ◽  
Surface Winds ◽  
Near Surface ◽  
Sea Surface Winds ◽  
Direct Radiative Forcing

Abstract. Collocated measurements of spectral aerosol optical depths (AODs), total and BC mass concentrations, and number size distributions of near surface aerosols, along with sea surface winds, made onboard a scientific cruise over southeastern Arabian Sea, are used to delineate the effects of changes in the wind speed on aerosol properties and its implication on the shortwave and longwave radiative forcing. The results indicated that an increase in the sea-surface wind speed from calm to moderate (<1 to 8 m s−1) values results in a selective increase of the particle concentrations in the size range 0.5 to 5 μm, leading to significant changes in the size distribution, increase in the mass concentration, decrease in the BC mass fraction, a remarkable increase in AODs in the near infrared and a flattening of the AOD spectrum. The consequent increase in the longwave direct radiative forcing almost entirely offsets the corresponding increase in the short wave direct radiative forcing (or even overcompensates) at the top of the atmosphere; while the surface forcing is offset by about 50%.

scholarly journals The Probability Distribution of Sea Surface Wind Speeds: Effects of Variable Surface Stratification and Boundary Layer Thickness

2010 ◽  
Vol 23 (19) ◽  
pp. 5151-5162 ◽  
Author(s):  
Adam Hugh Monahan
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Surface Wind ◽  
Sea Surface ◽  
Surface Winds ◽  
Free Atmosphere ◽  
Wind Speeds ◽  
Sea Surface Wind ◽  
Variable Surface

Abstract Air–sea exchanges of momentum, energy, and material substances of fundamental importance to the variability of the climate system are mediated by the character of the turbulence in the atmospheric and oceanic boundary layers. Sea surface winds influence, and are influenced by, these fluxes. The probability density function (pdf) of sea surface wind speeds p(w) is a mathematical object describing the variability of surface winds that arises from the physics of the turbulent atmospheric planetary boundary layer. Previous mechanistic models of the pdf of sea surface wind speeds have considered the momentum budget of an atmospheric layer of fixed thickness and neutral stratification. The present study extends this analysis, using an idealized model to consider the influence of boundary layer thickness variations and nonneutral surface stratification on p(w). It is found that surface stratification has little direct influence on p(w), while variations in boundary layer thickness bring the predictions of the model into closer agreement with the observations. Boundary layer thickness variability influences the shape of p(w) in two ways: through episodic downward mixing of momentum into the boundary layer from the free atmosphere and through modulation of the importance (relative to other tendencies) of turbulent momentum fluxes at the surface and the boundary layer top. It is shown that the second of these influences dominates over the first.

scholarly journals Fifty-Seven-Year California Reanalysis Downscaling at 10 km (CaRD10). Part I: System Detail and Validation with Observations

2007 ◽  
Vol 20 (22) ◽  
pp. 5553-5571 ◽  
Author(s):  
Masao Kanamitsu ◽  
Hideki Kanamaru
Keyword(s):  
Time Scales ◽  
Large Scale ◽  
Global Analysis ◽  
Regional Climate ◽  
Regional Scale ◽  
Surface Wind ◽  
Lateral Boundary ◽  
Climate Change Research ◽  
Near Surface ◽  
Precipitation Analysis

Abstract For the purpose of producing datasets for regional-scale climate change research and application, the NCEP–NCAR reanalysis for the period 1948–2005 was dynamically downscaled to hourly, 10-km resolution over California using the Regional Spectral Model. This is Part I of a two-part paper, describing the details of the downscaling system and comparing the downscaled analysis [California Reanalysis Downscaling at 10 km (CaRD10)] against observation and global analysis. An extensive validation of the downscaled analysis was performed using station observations, Higgins gridded precipitation analysis, and Precipitation-Elevation Regression on Independent Slopes Model (PRISM) precipitation analysis. In general, the CaRD10 near-surface wind and temperature fit better to regional-scale station observations than the NCEP–NCAR reanalysis used to force the regional model, supporting the premise that the regional downscaling is a viable method to attain regional detail from large-scale analysis. This advantage of CaRD10 was found on all time scales, ranging from hourly to decadal scales (i.e., from diurnal variation to multidecadal trend). Dynamically downscaled analysis provides ways to study various regional climate phenomena of different time scales because all produced variables are dynamically, physically, and hydrologically consistent. However, the CaRD10 is not free from problems. It suffers from positive bias in precipitation for heavy precipitation events. The CaRD10 is inaccurate near the lateral boundary where regional detail is damped by the lateral boundary relaxation. It is important to understand these limitations before the downscaled analysis is used for research.

Assessment of energy resources of Polish Baltic Sea areas

2017 ◽  
Vol 32 (1) ◽  
pp. 93-102
Author(s):  
Maciej Kałas ◽  
Piotr Piotrowski
Keyword(s):  
Power Plants ◽  
Numerical Models ◽  
Wind Waves ◽  
Surface Wind ◽  
Sea Surface ◽  
Energy Resources ◽  
Near Surface ◽  
Sea Surface Wind ◽  
Physical Energy ◽  
Physical Phenomena

The article presents spatial characteristics of energy fluxes recorded in the area of the Polish Exclusive Economic Zone (EEZ) in the four-year period of 2013–16. Data presented in this work are based on results of forecast calculations with the application of numerical models of the atmosphere (HIRLAM) and sea (WAM and HIROMB). Conducted analyses were concerned with dynamics of physical phenomena above the sea surface (wind), on its surface (wind waves motion), and in its near-surface layer up to 4 m (seawater flows). Physical energy resources connected with these processes for subsequent four years were computed and compared with the amount of annual electricity output generated by conventional and renewable sources of energy. Such an analysis of estimated energy resources reveals that the resource is highly differentiated in terms of space and in individual years, and significantly exceed the annual production of Polish power plants.

scholarly journals An Assessment of NASA’s GMAO MERRA-2 Reanalysis Surface Winds

2019 ◽  
Vol 32 (23) ◽  
pp. 8261-8281 ◽  
Author(s):  
D. Carvalho
Keyword(s):  
Surface Wind ◽  
The Other ◽  
Surface Winds ◽  
Wind Fields ◽  
Near Surface ◽  
Wind Speeds ◽  
Wide Range ◽  
Ocean Surface Winds ◽  
The Tropics ◽  
Global Surface

Abstract The quality of MERRA-2 surface wind fields was assessed by comparing them with 10 years of measurements from a wide range of surface wind observing platforms. This assessment includes a comparison of MERRA-2 global surface wind fields with the ones from its predecessor, MERRA, to assess if GMAO’s latest reanalyses improved the representation of the global surface winds. At the same time, surface wind fields from other modern reanalyses—NCEP-CFSR, ERA-Interim, and JRA-55—were also included in the comparisons to evaluate MERRA-2 global surface wind fields in the context of its contemporary reanalyses. Results show that MERRA-2, CFSR, ERA-Interim, and JRA-55 show similar error metrics while MERRA consistently shows the highest errors. Thus, when compared with wind observations, the accuracy of MERRA-2 surface wind fields represents a clear improvement over its predecessor MERRA and is in line with the other contemporary reanalyses in terms of the representation of global near-surface wind fields. All reanalyses showed a tendency to underestimate ocean surface winds (particularly in the tropics) and, oppositely, to overestimate inland surface winds (except JRA-55, which showed a global tendency to underestimate the wind speeds); to represent the wind direction rotated clockwise in the Northern Hemisphere (positive bias) and anticlockwise in the Southern Hemisphere (negative bias), with the exception of JRA-55; and to show higher errors near the poles and in the ITCZ, particularly in the equatorial western coasts of Central America and Africa. However, MERRA-2 showed substantially lower wind errors in the poles when compared with the other reanalyses.

scholarly journals High-resolution observations of the near-surface wind field over an isolated mountain and in a steep river canyon

2015 ◽  
Vol 15 (7) ◽  
pp. 3785-3801 ◽  
Author(s):  
B. W. Butler ◽  
N. S. Wagenbrenner ◽  
J. M. Forthofer ◽  
B. K. Lamb ◽  
K. S. Shannon ◽  
...  
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
Surface Wind ◽  
Wind Data ◽  
Wind Flow ◽  
Surface Winds ◽  
Mean Flow ◽  
Near Surface ◽  
Wind Speeds ◽  
Synoptic Forcing

Abstract. A number of numerical wind flow models have been developed for simulating wind flow at relatively fine spatial resolutions (e.g., ~ 100 m); however, there are very limited observational data available for evaluating these high-resolution models. This study presents high-resolution surface wind data sets collected from an isolated mountain and a steep river canyon. The wind data are presented in terms of four flow regimes: upslope, afternoon, downslope, and a synoptically driven regime. There were notable differences in the data collected from the two terrain types. For example, wind speeds on the isolated mountain increased with distance upslope during upslope flow, but generally decreased with distance upslope at the river canyon site during upslope flow. In a downslope flow, wind speed did not have a consistent trend with position on the isolated mountain, but generally increased with distance upslope at the river canyon site. The highest measured speeds occurred during the passage of frontal systems on the isolated mountain. Mountaintop winds were often twice as high as wind speeds measured on the surrounding plain. The highest speeds measured in the river canyon occurred during late morning hours and were from easterly down-canyon flows, presumably associated with surface pressure gradients induced by formation of a regional thermal trough to the west and high pressure to the east. Under periods of weak synoptic forcing, surface winds tended to be decoupled from large-scale flows, and under periods of strong synoptic forcing, variability in surface winds was sufficiently large due to terrain-induced mechanical effects (speed-up over ridges and decreased speeds on leeward sides of terrain obstacles) that a large-scale mean flow would not be representative of surface winds at most locations on or within the terrain feature. These findings suggest that traditional operational weather model (i.e., with numerical grid resolutions of around 4 km or larger) wind predictions are not likely to be good predictors of local near-surface winds on sub-grid scales in complex terrain. Measurement data can be found at http://www.firemodels.org/index.php/windninja-introduction/windninja-publications.

scholarly journals Parametric Estimation of the Stochastic Dynamics of Sea Surface Winds

2014 ◽  
Vol 71 (9) ◽  
pp. 3465-3483 ◽  
Author(s):  
William F. Thompson ◽  
Adam H. Monahan ◽  
Daan Crommelin
Keyword(s):  
Time Series ◽  
Stochastic Dynamics ◽  
Surface Wind ◽  
Estimation Procedure ◽  
Parametric Estimation ◽  
Sea Surface ◽  
Parameter Estimates ◽  
Model Parameters ◽  
Surface Winds ◽  
Sea Surface Winds

Abstract In this study, the parameters of a stochastic–dynamical model of sea surface winds are estimated from long time series of sea surface wind observational data. The model was introduced by A. H. Monahan, who developed an idealized model from a highly simplified representation of the momentum budget of a surface atmospheric layer of fixed depth. Such estimation of model parameters is challenging, in particular for a multivariate model with nonlinear terms as is considered here. The authors use a method developed recently by Crommelin and Vanden-Eijnden, which approaches the estimation problem variationally, finding the spectrally “best fit” stochastic differential equation to a time series of observations. While the estimation procedure assumes forcing that is white in time, observed time series are generally better approximated as forced by red noise. Using a red-noise-forced linear system, the authors first show that the estimation procedure can still be used to estimate model parameters. Because the assumption of white noise is violated, these estimates lead to model autocorrelation functions that differ from the observed time series. Application of the estimation procedure to the wind data is further complicated by the fact that the boundary layer model is inconsistent with certain observed features of the wind. When these mismatches between the model and observations are accounted for, the estimation procedure generally results in parameter estimates consistent with the climatological features of the associated meteorological fields. Important exceptions to this result are the layer thickness and layer-top eddy diffusivity, which are poorly estimated where the vector winds are close to Gaussian.

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