scholarly journals Prevailing Surface Wind Direction during Air–Sea Heat Exchange

2019 ◽  
Vol 32 (17) ◽  
pp. 5601-5617 ◽  
Author(s):  
Fumiaki Ogawa ◽  
Thomas Spengler
Keyword(s):  
Heat Exchange ◽  
Time Scales ◽  
Wind Direction ◽  
Surface Wind ◽  
Reanalysis Data ◽  
Heat Fluxes ◽  
Prevailing Wind ◽  
Prevailing Wind Direction ◽  
Mean Wind Speed ◽  
Time Averages

AbstractWhile the climatological-mean sensible and latent heat fluxes are remarkably well described using climatological-mean fields in the bulk flux formulas, this study shows that a significant fraction of the climatological-mean wind speed in the midlatitudes is associated with wind variations on synoptic time scales. Hence, the prevailing wind direction associated with the most intense air–sea heat exchange can differ from the mean wind direction. To pinpoint these striking differences between the climatological and synoptic viewpoint, this study presents a global climatology of the prevailing surface wind direction during air–sea heat exchanges calculated for instantaneous and time-averaged reanalysis data. The interpretation of the fluxes in the lower latitudes is basically unaffected by the different time averages, highlighting the time-mean nature of the circulation in the lower latitudes. In the midlatitudes, however, the prevailing wind direction features a significant equatorward component for subweekly time averages and reverts to pure westerlies for longer time averages. These findings pinpoint the necessity to consider subweekly time scales, in particular along the midlatitude SST fronts, to describe the air–sea heat exchange in a physically consistent way.

scholarly journals Spatiotemporal Characteristics of Near-Surface Wind in Shenzhen

2020 ◽  
Vol 12 (2) ◽  
pp. 739 ◽  
Author(s):  
Cheng Liu ◽  
Qinglan Li ◽  
Wei Zhao ◽  
Yuqing Wang ◽  
Riaz Ali ◽  
...  
Keyword(s):  
Wind Speed ◽  
Wind Direction ◽  
Surface Wind ◽  
Prevailing Wind ◽  
Average Wind Speed ◽  
Near Surface ◽  
Average Wind ◽  
Prevailing Wind Direction ◽  
Seasonal Wind ◽  
The Mean

The spatiotemporal characteristics of near-surface wind in Shenzhen were investigated in this study by using hourly observations at 92 automatic weather stations (AWSs) from 2009 to 2018. The results show that during the past 10 years, most of the stations showed a decreasing trend in the annual mean of the 10 min average wind speed (avg-wind) and the mean of the 3 s average wind speed (gust wind). Over half of the decreasing trends at the stations were statistically significant (p < 0.05). Seasonally, the decrease in wind speed was the most severe in spring, followed by autumn, winter, and summer. The distribution of wind speed tends to be greater in the east and coastal areas for both avg-wind and gust wind. From September to March of the following year, the prevailing wind direction in Shenzhen was northerly, and from April to August, the prevailing wind direction was southerly. The seasonal wind speed distribution exhibited two different types, spring–summer type and autumn–winter type, which may be induced by their different prevailing wind directions. The analysis by the empirical orthogonal function (EOF) method confirmed the previous findings that the mean wind speed was decreasing in Shenzhen and that two different seasonal wind speed spatial distribution patterns existed. Such a study could provide references for wind forecasting and risk assessment in the study area.

scholarly journals Properties of the Wind Field within the Oklahoma City Park Avenue Street Canyon. Part I: Mean Flow and Turbulence Statistics

2007 ◽  
Vol 46 (12) ◽  
pp. 2038-2054 ◽  
Author(s):  
M. A. Nelson ◽  
E. R. Pardyjak ◽  
J. C. Klewicki ◽  
S. U. Pol ◽  
M. J. Brown
Keyword(s):  
Wind Direction ◽  
Street Canyon ◽  
Sonic Anemometer ◽  
Surface Wind ◽  
Oklahoma City ◽  
Prevailing Wind ◽  
Advective Transport ◽  
Mean Flow ◽  
Prevailing Wind Direction ◽  
The Mean

Abstract Velocity data were obtained from sonic anemometer measurements within an east–west-running street canyon located in the urban core of Oklahoma City, Oklahoma, during the Joint Urban 2003 field campaign. These data were used to explore the directional dependence of the mean flow and turbulence within a real-world street canyon. The along-canyon vortex that is a key characteristic of idealized street canyon studies was not evident in the mean wind data, although the sensor placement was not optimized for the detection of such structures. Instead, surface wind measurements imply that regions of horizontal convergence and divergence exist within the canopy, which are likely caused by taller buildings diverting the winds aloft down into the canopy. The details of these processes appear to be dependent on relatively small perturbations in the prevailing wind direction. Turbulence intensities within the canyon interior appeared to have more dependence on prevailing wind direction than they did in the intersections. Turbulence in the intersections tended to be higher than was observed in the canyon interior. This behavior implies that there are some fundamental differences between the flow structure found in North American–style cities where building heights are typically heterogeneous and that found in European-style cities, which generally have more homogeneous building heights. It is hypothesized that the greater three-dimensionality caused by the heterogeneous building heights increases the ventilation of the urban canopy through mean advective transport as well as enhanced turbulence.

scholarly journals Evaluating multi-year, multi-site data on the energy balance closure of eddy-covariance flux measurements at cropland sites in southwestern Germany

2019 ◽  
Vol 16 (2) ◽  
pp. 521-540 ◽  
Author(s):  
Ravshan Eshonkulov ◽  
Arne Poyda ◽  
Joachim Ingwersen ◽  
Hans-Dieter Wizemann ◽  
Tobias K. D. Weber ◽  
...  
Keyword(s):  
Energy Balance ◽  
Eddy Covariance ◽  
Wind Direction ◽  
Climate Models ◽  
Global Climate Models ◽  
Energy Balance Closure ◽  
Prevailing Wind ◽  
Atmospheric Conditions ◽  
Prevailing Wind Direction ◽  
Wide Range

Abstract. The energy balance of eddy-covariance (EC) measurements is typically not closed, resulting in one of the main challenges in evaluating and interpreting EC flux data. Energy balance closure (EBC) is crucial for validating and improving regional and global climate models. To investigate the nature of the gap in EBC for agroecosystems, we analyzed EC measurements from two climatically contrasting regions (Kraichgau – KR – and Swabian Jura – SJ) in southwestern Germany. Data were taken at six fully equipped EC sites from 2010 to 2017. The gap in EBC was quantified by ordinary linear regression, relating the energy balance ratio (EBR), calculated as the quotient of turbulent fluxes and available energy, to the residual energy term. In order to examine potential reasons for differences in EBC, we compared the EBC under varying environmental conditions and investigated a wide range of possible controls. Overall, the variation in EBC was found to be higher during winter than summer. Moreover, we determined that the site had a statistically significant effect on EBC but no significant effect on either crop or region (KR vs SJ). The time-variable footprints of all EC stations were estimated based on data measured in 2015, complimented by micro-topographic analyses along the prevailing wind direction. The smallest mean annual energy balance gap was 17 % in KR and 13 % in SJ. Highest EBRs were mostly found for winds from the prevailing wind direction. The spread of EBRs distinctly narrowed under unstable atmospheric conditions, strong buoyancy, and high friction velocities. Smaller footprint areas led to better EBC due to increasing homogeneity. Flow distortions caused by the back head of the anemometer negatively affected EBC during corresponding wind conditions.

scholarly journals Dynamical Attribution of Recent Variability in Atlantic Overturning

2016 ◽  
Vol 29 (9) ◽  
pp. 3339-3352 ◽  
Author(s):  
Helen R. Pillar ◽  
Patrick Heimbach ◽  
Helen L. Johnson ◽  
David P. Marshall
Keyword(s):  
Time Series ◽  
Time Scales ◽  
Surface Wind ◽  
Heat Fluxes ◽  
Meridional Overturning Circulation ◽  
Buoyancy Forcing ◽  
Freshwater Forcing ◽  
Decadal Trend ◽  
Improved Model ◽  
Short Time

Abstract Attributing observed variability of the Atlantic meridional overturning circulation (AMOC) to past changes in surface forcing is challenging but essential for detecting any influence of anthropogenic forcing and reducing uncertainty in future climate predictions. Here, quantitative estimates of separate contributions from wind and buoyancy forcing to AMOC variations at 25°N are obtained. These estimates are achieved by projecting observed atmospheric anomalies onto model-based dynamical patterns of AMOC sensitivity to surface wind, thermal, and freshwater forcing over the preceding 15 years. Local wind forcing is shown to dominate AMOC variability on short time scales, whereas subpolar heat fluxes dominate on decadal time scales. The reconstructed transport time series successfully reproduces most of the interannual variability observed by RAPID–MOCHA. However, the apparent decadal trend in the RAPID–MOCHA time series is not captured, requiring improved model representation of ocean adjustment to subpolar heat fluxes over at least the past two decades and highlighting the importance of sustained monitoring of the high-latitude North Atlantic.

scholarly journals The Occurrences and Formation of Ladderback Ripples on Barchans Dunes of Najaf Dunes Field, Iraq, in Aeolian Environments

2021 ◽  
pp. 1598-1604
Author(s):  
Ahmed Jawad Al-Naji ◽  
Hasan Kattoof Jasim ◽  
Mazin Y. Tamar-Agha ◽  
Thamer Abaas Al-Shammery
Keyword(s):  
Wind Direction ◽  
Prevailing Wind ◽  
Fine Grained ◽  
Prevailing Wind Direction ◽  
Barchan Dunes ◽  
Light Mineral ◽  
Sand Sediments

This paper concerns the study of ripples that occur on the windward of Barchan dunes from the dunes field of Najaf governorate, Iraq. These dunes consist mainly of sand sediments with variable sizes, including medium, fine, and very fine sands. Quartz represents the major light mineral in the Najaf Dunes sand. The prevailing wind direction in the study area is NW-SE. The major ripple crest series of every pattern are oriented perpendicular to the NW-SE wind direction, whereas imbricated ripple groups within the troughs of the preexisting ripples are created by the WSW-ENE wind trend. These ripples tend to be formed by shortened ripples that occupy the troughs of the prolonged series. All crests of the ladderback ripples are oriented at right angles to asymmetry ripples. The ladderback ripples were noticed from fine to very fine- grained sediments, which consist mainly of quartz. The wavelength of the ladderback ripples ranges from 2 – 4 cm, while they are 0.1 – 0.2 cm in height. The occurrence of ladderback ripples within an aeolian environment indicates a variety of wind directions, which influenced the arrangements of the crest ripples.

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