scholarly journals Vertical velocity statistics in continental stratocumulus as measured by a 94GHz radar

1999 ◽  
Vol 26 (8) ◽  
pp. 1177-1180 ◽  
Author(s):  
D. M. Babb ◽  
J. Verlinde
Keyword(s):  
Vertical Velocity ◽  
Velocity Statistics

scholarly journals Cloud-base vertical velocity statistics: a comparison between an atmospheric mesoscale model and remote sensing observations

2011 ◽  
Vol 11 (3) ◽  
pp. 9607-9633
Author(s):  
J. Tonttila ◽  
E. J. O'Connor ◽  
S. Niemelä ◽  
P. Räisänen ◽  
H. Järvinen
Keyword(s):  
Remote Sensing ◽  
Standard Deviation ◽  
Vertical Velocity ◽  
Mesoscale Model ◽  
Horizontal Resolution ◽  
Cloud Base ◽  
Special Treatment ◽  
Grid Spacing ◽  
Velocity Statistics ◽  
Aerosol Cloud Interactions

Abstract. The statistics of cloud-base vertical velocity simulated by the non-hydrostatic mesoscale model AROME are compared with Cloudnet remote sensing observations at two locations: the ARM SGP site in Central Oklahoma, and the DWD observatory at Lindenberg, Germany. The results show that, as expected, AROME significantly underestimates the variability of vertical velocity at cloud-base compared to observations at their nominal resolution; the standard deviation of vertical velocity in the model is typically 4–6 times smaller than observed, and even more during the winter at Lindenberg. Averaging the observations to the horizontal scale corresponding to the physical grid spacing of AROME (2.5 km) explains 70–80% of the underestimation by the model. Further averaging of the observations in the horizontal is required to match the model values for the standard deviation in vertical velocity. This indicates an effective horizontal resolution for the AROME model of at least 4 times the physically-defined grid spacing. The results illustrate the need for special treatment of sub-grid scale variability of vertical velocities in kilometer-scale atmospheric models, if processes such as aerosol-cloud interactions are to be included in the future.

scholarly journals Multiyear Summertime Observations of Daytime Fair-Weather Cumuli at the ARM Southern Great Plains Facility

2013 ◽  
Vol 26 (24) ◽  
pp. 10031-10050 ◽  
Author(s):  
Arunchandra S. Chandra ◽  
Pavlos Kollias ◽  
Bruce A. Albrecht
Keyword(s):  
Great Plains ◽  
Vertical Velocity ◽  
Fair Weather ◽  
Cumulus Clouds ◽  
Cloud Droplets ◽  
Geometrical Properties ◽  
Southern Great Plains ◽  
Aspect Ratios ◽  
Velocity Statistics ◽  
Atmospheric Radiation Measurement

Abstract A long data record (14 yr) of ground-based observations at the Atmospheric Radiation Measurement Program (ARM) Southern Great Plains (SGP) site is analyzed to document the macroscopic and dynamical properties of daytime fair-weather cumulus clouds during summer months. First, a fuzzy logic–based algorithm is developed to eliminate insect radar echoes in the boundary layer that hinder the ability to develop representative cloud statistics. The refined dataset is used to document the daytime composites of fair-weather cumulus clouds properties. Doppler velocities are processed for lower reflectivity thresholds that contain small cloud droplets having insignificant terminal velocities; thus, Doppler velocities are used as tracers of air motion. The algorithm is implemented to process the entire 14-yr dataset of cloud radar vertical velocity data. Composite diurnal variations of the cloud vertical velocity statistics, surface parameters, and profiles of updraft and downdraft fractions, bulk velocity of updrafts and downdrafts, and updraft and downdraft mass flux are calculated. Statistics on the cloud geometrical properties such as cloud thickness, cloud chord length, cloud spacing, and aspect ratios are calculated on the cloud scale. The present dataset provides a unique insight into the daytime evolution and statistical description of the turbulent structure inside fair-weather cumuli over land.

scholarly journals Improvement of vertical velocity statistics measured by a Doppler lidar through comparison with sonic anemometer observations

2016 ◽  
Vol 9 (12) ◽  
pp. 5833-5852 ◽  
Author(s):  
Timothy A. Bonin ◽  
Jennifer F. Newman ◽  
Petra M. Klein ◽  
Phillip B. Chilson ◽  
Sonia Wharton
Keyword(s):  
Vertical Velocity ◽  
Close Agreement ◽  
Sonic Anemometer ◽  
Lag Time ◽  
Volume Averaging ◽  
Doppler Lidar ◽  
Established Method ◽  
Velocity Statistics ◽  
Sonic Anemometers ◽  
Velocity Variance

Abstract. Since turbulence measurements from Doppler lidars are being increasingly used within wind energy and boundary-layer meteorology, it is important to assess and improve the accuracy of these observations. While turbulent quantities are measured by Doppler lidars in several different ways, the simplest and most frequently used statistic is vertical velocity variance (w′2) from zenith stares. However, the competing effects of signal noise and resolution volume limitations, which respectively increase and decrease w′2, reduce the accuracy of these measurements. Herein, an established method that utilises the autocovariance of the signal to remove noise is evaluated and its skill in correcting for volume-averaging effects in the calculation of w′2 is also assessed. Additionally, this autocovariance technique is further refined by defining the amount of lag time to use for the most accurate estimates of w′2. Through comparison of observations from two Doppler lidars and sonic anemometers on a 300 m tower, the autocovariance technique is shown to generally improve estimates of w′2. After the autocovariance technique is applied, values of w′2 from the Doppler lidars are generally in close agreement (R2 ≈ 0.95 − 0.98) with those calculated from sonic anemometer measurements.

scholarly journals Cloud base vertical velocity statistics: a comparison between an atmospheric mesoscale model and remote sensing observations

2011 ◽  
Vol 11 (17) ◽  
pp. 9207-9218 ◽  
Author(s):  
J. Tonttila ◽  
E. J. O'Connor ◽  
S. Niemelä ◽  
P. Räisänen ◽  
H. Järvinen
Keyword(s):  
Remote Sensing ◽  
Standard Deviation ◽  
Vertical Velocity ◽  
Mesoscale Model ◽  
Grid Point ◽  
Horizontal Resolution ◽  
Careful Consideration ◽  
Cloud Base ◽  
Special Treatment ◽  
Velocity Statistics

Abstract. The statistics of cloud base vertical velocity simulated by the non-hydrostatic mesoscale model AROME are compared with Cloudnet remote sensing observations at two locations: the ARM SGP site in central Oklahoma, and the DWD observatory at Lindenberg, Germany. The results show that AROME significantly underestimates the variability of vertical velocity at cloud base compared to observations at their nominal resolution; the standard deviation of vertical velocity in the model is typically 4–8 times smaller than observed, and even more during the winter at Lindenberg. Averaging the observations to the horizontal scale corresponding to the physical grid spacing of AROME (2.5 km) explains 70–80 % of the underestimation by the model. Further averaging of the observations in the horizontal is required to match the model values for the standard deviation in vertical velocity. This indicates an effective horizontal resolution for the AROME model of at least 10 km in the presented case. Adding a TKE-term on the resolved grid-point vertical velocity can compensate for the underestimation, but only for altitudes below approximately the boundary layer top height. The results illustrate the need for a careful consideration of the scales the model is able to accurately resolve, as well as for a special treatment of sub-grid scale variability of vertical velocities in kilometer-scale atmospheric models, if processes such as aerosol-cloud interactions are to be included in the future.

scholarly journals Turbulent structure and scaling of the inertial subrange in a stratocumulus-topped boundary layer observed by a Doppler lidar

2015 ◽  
Vol 15 (10) ◽  
pp. 5873-5885 ◽  
Author(s):  
J. Tonttila ◽  
E. J. O'Connor ◽  
A. Hellsten ◽  
A. Hirsikko ◽  
C. O'Dowd ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Vertical Velocity ◽  
Marine Boundary Layer ◽  
Turbulent Structure ◽  
Inertial Subrange ◽  
Doppler Lidar ◽  
Turbulent Dissipation ◽  
Additional Information ◽  
Velocity Statistics ◽  
Velocity Skewness

Abstract. The turbulent structure of a stratocumulus-topped marine boundary layer over a 2-day period is observed with a Doppler lidar at Mace Head in Ireland. Using profiles of vertical velocity statistics, the bulk of the mixing is identified as cloud driven. This is supported by the pertinent feature of negative vertical velocity skewness in the sub-cloud layer which extends, on occasion, almost to the surface. Both coupled and decoupled turbulence characteristics are observed. The length and timescales related to the cloud-driven mixing are investigated and shown to provide additional information about the structure and the source of the mixing inside the boundary layer. They are also shown to place constraints on the length of the sampling periods used to derive products, such as the turbulent dissipation rate, from lidar measurements. For this, the maximum wavelengths that belong to the inertial subrange are studied through spectral analysis of the vertical velocity. The maximum wavelength of the inertial subrange in the cloud-driven layer scales relatively well with the corresponding layer depth during pronounced decoupled structure identified from the vertical velocity skewness. However, on many occasions, combining the analysis of the inertial subrange and vertical velocity statistics suggests higher decoupling height than expected from the skewness profiles. Our results show that investigation of the length scales related to the inertial subrange significantly complements the analysis of the vertical velocity statistics and enables a more confident interpretation of complex boundary layer structures using measurements from a Doppler lidar.

scholarly journals Improvement of Vertical Velocity Statistics Measured by a Doppler Lidar through Comparison with Sonic Anemometer Observations

2016 ◽  
Author(s):  
Timothy A. Bonin ◽  
Jennifer F. Newman ◽  
Petra M. Klein ◽  
Phillip B. Chilson ◽  
Sonia Wharton
Keyword(s):  
Vertical Velocity ◽  
Sonic Anemometer ◽  
Lag Time ◽  
Volume Averaging ◽  
Doppler Lidar ◽  
Atmospheric Conditions ◽  
Established Method ◽  
Velocity Statistics ◽  
Sonic Anemometers ◽  
Velocity Variance

Abstract. Since turbulence measurements from Doppler lidars are being increasingly used within wind energy and boundary-layer meteorology, it is important to assess and improve the accuracy of these observations. While turbulent quantities are measured by Doppler lidars in several different ways, the simplest and most frequently used statistic is vertical velocity variance (σ2ω) from zenith stares. However, the competing effects of signal noise and resolution volume limitations, which respectively increase and decrease σ2ω, reduce the accuracy of these measurements. Herein, an established method that utilizes the autocovariance of the signal to remove noise is evaluated and its skill in also correcting for volume-averaging effects in the calculation of σ2ω is assessed. Additionally, this autocovariance technique is further refined by defining the amount of lag time to use for the most accurate estimates of σ2ω. Through comparison of observations from two Doppler lidars and sonic anemometers on a 300-m tower, the autocovariance technique is shown to improve estimates of σ2ω over a variety of atmospheric conditions. After the autocoviance technique is applied, values of σ2ω from the Doppler lidars are generally in close agreement (R2 ≈ 0.95–0.98) with those calculated from sonic anemometer measurements.

scholarly journals Doppler Lidar Vertical Velocity Statistics Value-Added Product

2015 ◽  
Author(s):  
R. K. Newsom ◽  
◽  
C. Sivaraman ◽  
T. R. Shippert ◽  
L. D. Riihimaki
Keyword(s):  
Vertical Velocity ◽  
Value Added ◽  
Doppler Lidar ◽  
Velocity Statistics

scholarly journals Turbulent structure and scaling of the inertial subrange in a stratocumulus-topped boundary layer observed by a Doppler lidar

2014 ◽  
Vol 14 (17) ◽  
pp. 24119-24148
Author(s):  
J. Tonttila ◽  
E. J. O'Connor ◽  
A. Hellsten ◽  
A. Hirsikko ◽  
C. O'Dowd ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Vertical Velocity ◽  
Marine Boundary Layer ◽  
Turbulent Structure ◽  
Inertial Subrange ◽  
Relative Depth ◽  
Doppler Lidar ◽  
Turbulent Dissipation ◽  
Additional Information ◽  
Velocity Statistics

Abstract. The turbulent structure of a stratocumulus-topped marine boundary layer over a two-day period is observed with a Doppler lidar at Mace Head in Ireland. Using profiles of vertical velocity statistics, the bulk of the mixing is identified as cloud-driven. This is supported by the pertinent feature of negative vertical velocity skewness in the sub-cloud layer which extends, on occasion, almost to the surface. Both coupled and decoupled turbulence characteristics are observed. The length and time scales related to the cloud driven mixing are investigated, which are shown to provide additional information about the structure and the source of the mixing inside the boundary layer. They are also shown to place constraints on the length of the sampling periods used to derive products, such as the turbulent dissipation rate, from lidar measurements. For this, the upper cut-off wavelength of the inertial subrange is studied through spectral analysis of the vertical velocity. The bulk statistical profiles and the scaling of the inertial subrange show consistent behaviour as the boundary layer undergoes transitions between a coupled and decoupled stratocumulus layer. The cut-off wavelength of the inertial subrange does not appear to scale robustly with the relative depth of the local mixing regime at different altitudes during decoupled periods. Rather, the competition between surface-based and cloud-driven mixed layers suppresses the range of eddy sizes at all heights inside the boundary layer.

scholarly journals Statistics of vertical velocities in supercooled cloud layers over Leipzig and Praia measured with Doppler lidar

2017 ◽  
Author(s):  
Johannes Bühl ◽  
Patric Seifert ◽  
Ronny Engelmann ◽  
Julia Fruntke ◽  
Albert Ansmann
Keyword(s):  
Vertical Velocity ◽  
Supercooled Liquid ◽  
Mixed Phase ◽  
Pure Liquid ◽  
Doppler Lidar ◽  
Velocity Statistics ◽  
Cloud Dynamics ◽  
Phase Layers ◽  
Spatio Temporal ◽  
Formation Efficiency

Abstract. This study presents statistics of vertical air velocity at the bases of supercooled shallow cloud layers separately for mixed-phase and liquid-only clouds. For the first time, this statistics is compared for clouds observed over a sub-tropical site at Cape Verde (14.9° N, 26° W) and a mid-latitudinal site at Leipzig, Germany (51.3° N, 12.4° E). Phase properties and spatio-temporal extent of the cloud layers were obtained from combined observations with Doppler lidar, Raman polarization lidar, and cloud radar. The statistical properties of the vertical-velocity distributions in both mixed-phase and pure-liquid cloud layers are found to be similar at both measurement sites. Standard deviation of the vertical velocities at both sites was found to be 0.4 m s−1 and was also the same in pure-liquid and mixed-phase layers. Skewness groups around −0.4 for both sites, pointing to radiative cooling as the driver for the cloud turbulence. Occasionally, positive skewness in some cloud layers indicated external drivers, e.g., gravity waves, for the turbulence. From the observed similarity in the vertical-velocity statistics derived at the base of supercooled liquid cloud layers at Praia and Leipzig it can be concluded that other factors besides cloud dynamics are responsible for the differences in ice formation efficiency reported previously for both sites.

Sign in / Sign up

Export Citation Format

Share Document