Wind-turning over the atmospheric boundary layer in observations and models

2020 ◽  
Author(s):  
Gunilla Svensson ◽  
Jenny Lindvall ◽  
Joakim Pyykkö
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Climate Models ◽  
Similarity Theory ◽  
Rossby Number ◽  
Surface Drag ◽  
Turning Angle ◽  
Wind Speeds ◽  
The Vertical Distribution ◽  
Clear Increase

<p>As an attempt to find a way of evaluating the surface drag in global models, we have derived a climatology of the boundary-layer wind-turning angle over land (Lindvall and Svensson, 2019). It is based on radiosonde observations from 800 stations in the Integrated Global Radiosonde Archive (IGRA). The climatology and how the wind turning depend on a suite of parameters is analyzed. Results from previous studies indicating the importance of the planetary boundary layer (PBL) stratification for the angle of wind turning are confirmed. A clear increase in the wind-turning angle with wind speed, particularly for stratified conditions, is also evident. According to Rossby number similarity theory, the crossisobaric angle for a neutral and barotropic boundary layer decreases with the surface Rossby number, Ro. The IGRA observations indicate that this dependence on Ro might partly be linked to the dependence of the stratification on the wind speed, a dependence that seems to prevail even for the high wind speeds, a criterium that traditionally is used to approximate a neutral PBL. The vertical distribution of the turning of the wind is analyzed using the high resolution Stratospheric Processes And their Role in Climate (SPARC) data. For unstable cases, there is a maximum in the directional wind shear around the PBL top, whereas for the most stable class of cases there is a maximum near the surface. The midlatitude cross-isobaric mass transport is estimated using the IGRA data. The wind-turning angles from reanalysis fields and climate models are also presented, they generally underestimate the turning angle.</p>

scholarly journals Local Characteristics of the Nocturnal Boundary Layer in Response to External Pressure Forcing

2017 ◽  
Vol 56 (11) ◽  
pp. 3035-3047 ◽  
Author(s):  
Steven J. A. van der Linden ◽  
Peter Baas ◽  
J. Antoon van Hooft ◽  
Ivo G. S. van Hooijdonk ◽  
Fred C. Bosveld ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Stable Boundary Layer ◽  
Dynamical Behavior ◽  
Geostrophic Wind ◽  
External Pressure ◽  
Near Surface ◽  
Stable Boundary ◽  
Wind Speeds ◽  
Turbulent Characteristics

AbstractGeostrophic wind speed data, derived from pressure observations, are used in combination with tower measurements to investigate the nocturnal stable boundary layer at Cabauw, the Netherlands. Since the geostrophic wind speed is not directly influenced by local nocturnal stability, it may be regarded as an external forcing parameter of the nocturnal stable boundary layer. This is in contrast to local parameters such as in situ wind speed, the Monin–Obukhov stability parameter (z/L), or the local Richardson number. To characterize the stable boundary layer, ensemble averages of clear-sky nights with similar geostrophic wind speeds are formed. In this manner, the mean dynamical behavior of near-surface turbulent characteristics and composite profiles of wind and temperature are systematically investigated. The classification is found to result in a gradual ordering of the diagnosed variables in terms of the geostrophic wind speed. In an ensemble sense the transition from the weakly stable to very stable boundary layer is more gradual than expected. Interestingly, for very weak geostrophic winds, turbulent activity is found to be negligibly small while the resulting boundary cooling stays finite. Realistic numerical simulations for those cases should therefore have a comprehensive description of other thermodynamic processes such as soil heat conduction and radiative transfer.

scholarly journals Stable Atmospheric Boundary Layers and Diurnal Cycles: Challenges for Weather and Climate Models

2013 ◽  
Vol 94 (11) ◽  
pp. 1691-1706 ◽  
Author(s):  
A. A. M. Holtslag ◽  
G. Svensson ◽  
P. Baas ◽  
S. Basu ◽  
B. Beare ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Atmospheric Boundary Layer ◽  
Climate Models ◽  
Model Performance ◽  
Weather Forecast ◽  
The Arctic ◽  
Diurnal Cycles ◽  
Low Wind Speed ◽  
Weather And Climate

The representation of the atmospheric boundary layer is an important part of weather and climate models and impacts many applications such as air quality and wind energy. Over the years, the performance in modeling 2-m temperature and 10-m wind speed has improved but errors are still significant. This is in particular the case under clear skies and low wind speed conditions at night as well as during winter in stably stratified conditions over land and ice. In this paper, the authors review these issues and provide an overview of the current understanding and model performance. Results from weather forecast and climate models are used to illustrate the state of the art as well as findings and recommendations from three intercomparison studies held within the Global Energy and Water Exchanges (GEWEX) Atmospheric Boundary Layer Study (GABLS). Within GABLS, the focus has been on the examination of the representation of the stable boundary layer and the diurnal cycle over land in clear-sky conditions. For this purpose, single-column versions of weather and climate models have been compared with observations, research models, and large-eddy simulations. The intercomparison cases are based on observations taken in the Arctic, Kansas, and Cabauw in the Netherlands. From these studies, we find that even for the noncloudy boundary layer important parameterization challenges remain.

scholarly journals Revisiting the Definition of the Drag Coefficient in the Marine Atmospheric Boundary Layer

2010 ◽  
Vol 40 (10) ◽  
pp. 2325-2332 ◽  
Author(s):  
Richard J. Foreman ◽  
Stefan Emeis
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Atmospheric Boundary Layer ◽  
Drag Coefficient ◽  
Friction Velocity ◽  
Marine Boundary Layer ◽  
Marine Atmospheric Boundary Layer ◽  
Wind Speeds ◽  
Traditional Definition ◽  
Definition Of

Abstract A new functional form of the neutral drag coefficient for moderate to high wind speeds in the marine atmospheric boundary layer for a range of field measurements as reported in the literature is proposed. This new form is found to describe a wide variety of measurements recorded in the open ocean, coast, fetch-limited seas, and lakes, with almost one and the same set of parameters. This is the result of a reanalysis of the definition of the drag coefficient in the marine boundary layer, which finds that a constant is missing from the traditional definition of the drag coefficient. The constant arises because the neutral friction velocity over water surfaces is not directly proportional to the 10-m wind speed, a consequence of the transition to rough flow at low wind speeds. Within the rough flow regime, the neutral friction velocity is linearly dependent on the 10-m wind speed; consequently, within this rough regime, the new definition of the drag coefficient is not a function of the wind speed. The magnitude of the new definition of the neutral drag coefficient represents an upper limit to the magnitude of the traditional definition.

Impact of Surface Waves on Wind Stress under Low to Moderate Wind Conditions

2020 ◽  
Author(s):  
Sheng Chen ◽  
Fangli Qiao ◽  
Wenzheng Jiang ◽  
Jingsong Guo ◽  
Dejun Dai
Keyword(s):  
Surface Waves ◽  
Wind Stress ◽  
Climate Models ◽  
Similarity Theory ◽  
Ocean Surface Waves ◽  
China Sea ◽  
Wind Speeds ◽  
Mean Sea Surface ◽  
Wind Profiles ◽  
The Impact

<p>The impact of ocean surface waves on wind stress at the air–sea interface under low to moderate wind<br>conditions was systematically investigated based on a simple constant flux model and flux measurements<br>obtained from two coastal towers in the East China Sea and South China Sea. It is first revealed that the<br>swell-induced perturbations can reach a height of nearly 30m above the mean sea surface, and these perturbations<br>disturb the overlying airflow under low wind and strong swell conditions. The wind profiles severely<br>depart from the classical logarithmic profiles, and the deviations increase with the peak wave phase speeds. At<br>wind speeds of less than 4 m/s, an upward momentumtransfer from the wave to the atmosphere is predicted,<br>which is consistent with previous studies. A comparison between the observations and model indicates that<br>the wind stress calculated by the model is largely consistent with the observational wind stress when considering<br>the effects of surface waves, which provides a solution for accurately calculating wind stress in ocean<br>and climate models. Furthermore, the surface waves at the air–sea interface invalidate the traditional<br>Monin–Obukhov similarity theory (MOST), and this invalidity decreases as observational height increases.</p>

scholarly journals How much of the global aerosol optical depth is found in the boundary layer and free troposphere?

2017 ◽  
Author(s):  
Quentin Bourgeois ◽  
Annica M. L. Ekman ◽  
Jean-Baptiste Renard ◽  
Radovan Krejci ◽  
Abhay Devasthale ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Climate Models ◽  
Convective Transport ◽  
Free Troposphere ◽  
Range Transport ◽  
Aerosol Classification ◽  
The Tropics ◽  
The Vertical Distribution

Abstract. The global aerosol extinction from the CALIOP space lidar was used to compute aerosol optical depth (AOD) over a nine-year period (2007–2015) and partitioned between the boundary layer (BL) and the free troposphere (FT) using BL heights obtained from the ERA-Interim archive. The results show that the vertical distribution of AOD does not follow the diurnal cycle of the BL but remains similar between day and night highlighting the presence of a residual layer during night. The BL and FT contribute 69 % and 31 %, respectively, to the global tropospheric AOD during daytime in line with observations obtained using the Light Optical Aerosol Counter (LOAC) instrument. The FT AOD contribution is larger in the tropics than at mid-latitudes which indicates that convective transport largely controls the vertical profile of aerosols. Over oceans, the FT AOD contribution is mainly governed by long-range transport of aerosols from emission sources located within neighboring continents. According to the CALIOP aerosol classification, dust and smoke particles are the main aerosol types transported into the FT. Overall, the study shows that the fraction of AOD in the FT – and thus potentially located above low-level clouds – is substantial and deserves more attention when evaluating the radiative effect of aerosols in climate models. More generally, the results have implications for process determining the overall budgets, sources, sinks and transport of aerosol particles and their description in atmospheric models.

scholarly journals Factors driving the seasonal and hourly variability of sea-spray aerosol number in the North Atlantic

2019 ◽  
Vol 116 (41) ◽  
pp. 20309-20314 ◽  
Author(s):  
Georges Saliba ◽  
Chia-Li Chen ◽  
Savannah Lewis ◽  
Lynn M. Russell ◽  
Laura-Helena Rivellini ◽  
...  
Keyword(s):  
Wind Speed ◽  
North Atlantic ◽  
Climate Models ◽  
Marine Boundary Layer ◽  
Phytoplankton Bloom ◽  
Cloud Condensation Nuclei ◽  
Sea Spray ◽  
Wind Speeds ◽  
The North ◽  
Sea Spray Aerosol

Four North Atlantic Aerosol and Marine Ecosystems Study (NAAMES) field campaigns from winter 2015 through spring 2018 sampled an extensive set of oceanographic and atmospheric parameters during the annual phytoplankton bloom cycle. This unique dataset provides four seasons of open-ocean observations of wind speed, sea surface temperature (SST), seawater particle attenuation at 660 nm (cp,660, a measure of ocean particulate organic carbon), bacterial production rates, and sea-spray aerosol size distributions and number concentrations (NSSA). The NAAMES measurements show moderate to strong correlations (0.56 < R < 0.70) between NSSA and local wind speeds in the marine boundary layer on hourly timescales, but this relationship weakens in the campaign averages that represent each season, in part because of the reduction in range of wind speed by multiday averaging. NSSA correlates weakly with seawater cp,660 (R = 0.36, P << 0.01), but the correlation with cp,660, is improved (R = 0.51, P < 0.05) for periods of low wind speeds. In addition, NAAMES measurements provide observational dependence of SSA mode diameter (dm) on SST, with dm increasing to larger sizes at higher SST (R = 0.60, P << 0.01) on hourly timescales. These results imply that climate models using bimodal SSA parameterizations to wind speed rather than a single SSA mode that varies with SST may overestimate SSA number concentrations (hence cloud condensation nuclei) by a factor of 4 to 7 and may underestimate SSA scattering (hence direct radiative effects) by a factor of 2 to 5, in addition to overpredicting variability in SSA scattering from wind speed by a factor of 5.

Investigation of weather conditions and tropospheric BrO transport during Bromine Explosion Events in the Arctic and ozone depletion in Ny-Ålesund observed by satellite and ground-based remote sensing

2021 ◽  
Author(s):  
Bianca Zilker ◽  
Anne-Marlene Blechschmidt ◽  
Sora Seo ◽  
Ilias Bougoudis ◽  
Tim Bösch ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Detection Limit ◽  
Wind Speed ◽  
Ozone Depletion ◽  
Weather Conditions ◽  
Tropospheric Chemistry ◽  
The Arctic ◽  
Blowing Snow ◽  
High Wind ◽  
Wind Speeds

&lt;p align=&quot;justify&quot;&gt;Bromine Explosion Events (BEEs) have been observed since the late 1990s in the Arctic and Antarctic during polar spring and play an important role in tropospheric chemistry. In a heterogeneous, autocatalytic, chemical chain reaction cycle, inorganic bromine is released from the cryosphere into the troposphere and depletes ozone often to below detection limit. Ozone is a source of the most important tropospheric oxidizing agent OH and the oxidizing capacity and radiative forcing of the troposphere are thus being impacted. Bromine also reacts with gaseous mercury, thereby facilitating the deposition of toxic mercury, which has adverse environmental impacts. C&lt;span lang=&quot;en-US&quot;&gt;old saline surfaces, such as young sea ice, frost flowers, and snow are likely bromine sources &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;during BEEs. &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;D&lt;/span&gt;ifferent meteorological conditions seem to favor the development of these events: on the one hand, low wind speeds and a stable boundary layer, where bromine can accumulate and deplete ozone, and on the other hand, high wind speeds above approximately 10 m/s with blowing snow and a higher unstable boundary layer. In high wind speed conditions &amp;#8211; occurring for example along fronts of polar cyclones &amp;#8211; recycling of bromine on snow and aerosol surfaces may take place aloft.&lt;/p&gt; &lt;p align=&quot;justify&quot;&gt;To improve the understanding of weather conditions and bromine sources leading to the development of BEEs, case studies using high resolution S5P TROPOMI retrievals of tropospheric BrO together with meteorological simulations by the WRF model and Lagrangian transport simulations of BrO by FLEXPART-WRF are carried out. WRF simulations show, that high tropospheric BrO columns observed by TROPOMI often coincide with areas of high wind speeds. This probably points to release of bromine from blowing snow with cold temperatures favoring the bromine explosion reactions. However, some BrO plumes are observed over areas with very low wind speed and a stable low boundary layer. To monitor the amount of ozone depleted during a BEE, ozone sonde measurements from Ny-&amp;#197;lesund are compared with MAX-DOAS BrO profiles. First evaluations show a drastic decrease in ozone, partly below the detection limit, while measuring enhanced BrO values at the same time. &lt;span lang=&quot;en-US&quot;&gt;In order to analyze &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;the possible origin&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt; of the BrO &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;plume &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;arriving in &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;Ny-&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;&amp;#197;&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;lesund&lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;, &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;and to investigate its transportation route, &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;FLEXPART-WRF runs are &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;executed &lt;/span&gt;&lt;span lang=&quot;en-US&quot;&gt;for the times of observed ozone depletion.&lt;/span&gt;&lt;/p&gt; &lt;p align=&quot;justify&quot;&gt;&amp;#160;&lt;/p&gt; &lt;p align=&quot;justify&quot;&gt;&lt;em&gt;This work was supported by the&lt;/em&gt;&lt;em&gt; DFG funded Transregio-project TR 172 &amp;#8220;Arctic Amplification &lt;/em&gt;(AC)&lt;sup&gt;3&lt;/sup&gt;&lt;em&gt;&amp;#8220;.&lt;/em&gt;&lt;/p&gt;

Impact of wind speeds on turbulent transport of carbon dioxide (CO2) fluxes at a tropical location in Ile - Ife, southwest Nigeria

2020 ◽  
Author(s):  
Theodora Bello ◽  
Adewale Ajao ◽  
Oluwagbemiga Jegede
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Land Surface ◽  
Stable Boundary Layer ◽  
Turbulent Transport ◽  
Strong Wind ◽  
Stable Boundary ◽  
Wind Speeds ◽  
Low Wind Speed ◽  
Tropical Area

&lt;p&gt;The study investigates impact of wind speeds on the turbulent transport of CO&lt;sub&gt;2 &lt;/sub&gt;fluxes for a land-surface atmosphere interface in a low-wind tropical area between May 28&lt;sup&gt;th&lt;/sup&gt; and June 14&lt;sup&gt;th&lt;/sup&gt;, 2010; and May 24&lt;sup&gt;th&lt;/sup&gt; and June 15&lt;sup&gt;th&lt;/sup&gt;, 2015. Eddy covariance technique was used to acquire turbulent mass fluxes of CO&lt;sub&gt;2&lt;/sub&gt; and wind speed at the study site located inside the main campus of Obafemi Awolowo University, Ile &amp;#8211; Ife, Nigeria. The results showed high levels of CO&lt;sub&gt;2 &lt;/sub&gt;fluxes at nighttime attributed to stable boundary layer conditions and low wind speed. Large transport and distribution of CO&lt;sub&gt;2 &lt;/sub&gt;fluxes were observed in the early mornings due to strong wind speeds recorded at the study location. In addition, negative CO&lt;sub&gt;2 &lt;/sub&gt;fluxes were observed during the daytime attributed to prominent convective and photosynthetic activities. The study concludes there was an inverse relationship between turbulent transport of CO&lt;sub&gt;2 &lt;/sub&gt;fluxes and wind speed for daytime period while nighttime CO&lt;sub&gt;2&lt;/sub&gt; fluxes showed no significant correlation.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Keywords&lt;/strong&gt;: CO&lt;sub&gt;2 &lt;/sub&gt;fluxes, Wind speed, Turbulent transport, Low-wind tropical area, Stable boundary layer&lt;/p&gt;

scholarly journals A Hurricane Boundary Layer and Wind Field Model for Use in Engineering Applications

2009 ◽  
Vol 48 (2) ◽  
pp. 381-405 ◽  
Author(s):  
Peter J. Vickery ◽  
Dhiraj Wadhera ◽  
Mark D. Powell ◽  
Yingzhao Chen
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Drag Coefficient ◽  
Wind Field ◽  
Field Model ◽  
Radial Dependence ◽  
Surface Winds ◽  
Wind Field Model ◽  
Wind Speeds ◽  
Hurricane Boundary Layer

Abstract This article examines the radial dependence of the height of the maximum wind speed in a hurricane, which is found to lower with increasing inertial stability (which in turn depends on increasing wind speed and decreasing radius) near the eyewall. The leveling off, or limiting value, of the marine drag coefficient in high winds is also examined. The drag coefficient, given similar wind speeds, is smaller for smaller-radii storms; enhanced sea spray by short or breaking waves is speculated as a cause. A fitting technique of dropsonde wind profiles is used to model the shape of the vertical profile of mean horizontal wind speeds in the hurricane boundary layer, using only the magnitude and radius of the “gradient” wind. The method slightly underestimates the surface winds in small but intense storms, but errors are less than 5% near the surface. The fit is then applied to a slab layer hurricane wind field model, and combined with a boundary layer transition model to estimate surface winds over both marine and land surfaces.

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