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 Sky cover from MFRSR observations: cumulus clouds

2011 ◽  
Vol 4 (1) ◽  
pp. 715-735 ◽  
Author(s):  
E. Kassianov ◽  
J. Barnard ◽  
L. K. Berg ◽  
C. Flynn ◽  
C. N. Long
Keyword(s):  
Great Plains ◽  
Visible Spectral Range ◽  
Department Of Energy ◽  
Cumulus Clouds ◽  
Southern Great Plains ◽  
Clear Sky ◽  
The Us ◽  
Atmospheric Radiation Measurement ◽  
Main Components ◽  
Good Agreement

Abstract. The diffuse all-sky surface irradiances measured at two nearby wavelengths in the visible spectral range and their model clear-sky counterparts are two main components of a new method for estimating the fractional sky cover of different cloud types, including cumulus clouds. The performance of this method is illustrated using 1-min resolution data from ground-based Multi-Filter Rotating Shadowband Radiometer (MFRSR). The MFRSR data are collected at the US Department of Energy Atmospheric Radiation Measurement (ARM) Climate Research Facility (ACRF) Southern Great Plains (SGP) site during the summer of 2007 and represent 13 days with cumulus clouds. Good agreement is obtained between estimated values of the fractional sky cover and those provided by a well-established independent method based on broadband observations.

Wide-Angle Imaging Lidar Deployment at the ARM Southern Great Plains Site: Intercomparison of Cloud Property Retrievals

2005 ◽  
Vol 22 (6) ◽  
pp. 628-648 ◽  
Author(s):  
Igor N. Polonsky ◽  
Steven P. Love ◽  
Anthony B. Davis
Keyword(s):  
Great Plains ◽  
Wide Angle ◽  
Geometrical Properties ◽  
Southern Great Plains ◽  
Geometrical Characteristics ◽  
New Instrument ◽  
Atmospheric Radiation Measurement ◽  
Lidar Return ◽  
Beam Component ◽  
Observation Period

Abstract The Wide-Angle Imaging Lidar (WAIL), a new instrument that measures cloud optical and geometrical properties by means of off-beam lidar returns, was deployed as part of a multi-instrument campaign to probe a cloud field at the Atmospheric Radiation Measurement (ARM) Southern Great Plain (SGP) site on 25 March 2002. WAIL is designed to determine physical and geometrical characteristics using the off-beam component of the lidar return that can be adequately modeled within the diffusion approximation. Using WAIL data, the extinction coefficient and geometrical thickness of a dense cloud layer is estimated, from which optical thickness is inferred. Results from the new methodology agree well with counterparts obtained from other instruments located permanently at the SGP ARM site and from the WAIL-like airborne instrument that flew over the site during our observation period.

scholarly journals Ground-Based Remote Retrievals of Cumulus Entrainment Rates

2013 ◽  
Vol 30 (7) ◽  
pp. 1460-1471 ◽  
Author(s):  
Timothy J. Wagner ◽  
David D. Turner ◽  
Larry K. Berg ◽  
Steven K. Krueger
Keyword(s):  
Great Plains ◽  
Optimal Estimation ◽  
Mean Value ◽  
Entrainment Rate ◽  
Cumulus Clouds ◽  
Sensitivity Testing ◽  
Southern Great Plains ◽  
Airborne Sampling ◽  
Estimation Scheme ◽  
Atmospheric Radiation Measurement

Abstract While fractional entrainment rates for cumulus clouds have typically been derived from airborne observations, this limits the size and scope of available datasets. To increase the number of continental cumulus entrainment rate observations available for study, an algorithm for retrieving them from ground-based remote sensing observations has been developed. This algorithm, called the Entrainment Rate In Cumulus Algorithm (ERICA), uses the suite of instruments at the Southern Great Plains (SGP) site of the U.S. Department of Energy's Atmospheric Radiation Measurement Program (ARM) Climate Research Facility as inputs into a Gauss–Newton optimal estimation scheme, in which an assumed guess of the entrainment rate is iteratively adjusted through intercomparison of modeled cloud attributes to their observed counterparts. The forward model in this algorithm is the explicit mixing parcel model (EMPM), a cloud parcel model that treats entrainment as a series of discrete entrainment events. A quantified value for the uncertainty in the retrieved entrainment rate is also returned as part of the retrieval. Sensitivity testing and information content analysis demonstrate the robust nature of this method for retrieving accurate observations of the entrainment rate without the drawbacks of airborne sampling. Results from a test of ERICA on 3 months of shallow cumulus cloud events show significant variability of the entrainment rate of clouds in a single day and from one day to the next. The mean value of 1.06 km−1 for the entrainment rate in this dataset corresponds well with prior observations and simulations of the entrainment rate in cumulus clouds.

scholarly journals Ground-based temperature and humidity profiling: combining active and passive remote sensors

2021 ◽  
Vol 14 (4) ◽  
pp. 3033-3048
Author(s):  
David D. Turner ◽  
Ulrich Löhnert
Keyword(s):  
Water Vapor ◽  
Information Content ◽  
Great Plains ◽  
Optimal Estimation ◽  
Differential Absorption ◽  
Southern Great Plains ◽  
Atmospheric Research ◽  
Remote Sensors ◽  
Central Portugal ◽  
Atmospheric Radiation Measurement

Abstract. Thermodynamic profiles in the planetary boundary layer (PBL) are important observations for a range of atmospheric research and operational needs. These profiles can be retrieved from passively sensed spectral infrared (IR) or microwave (MW) radiance observations or can be more directly measured by active remote sensors such as water vapor differential absorption lidars (DIALs). This paper explores the synergy of combining ground-based IR, MW, and DIAL observations using an optimal-estimation retrieval framework, quantifying the reduction in the uncertainty in the retrieved profiles and the increase in information content as additional observations are added to IR-only and MW-only retrievals. This study uses ground-based observations collected during the Perdigão field campaign in central Portugal in 2017 and during the DIAL demonstration campaign at the Atmospheric Radiation Measurement Southern Great Plains site in 2017. The results show that the information content in both temperature and water vapor is higher for the IR instrument relative to the MW instrument (thereby resulting in smaller uncertainties) and that the combined IR + MW retrieval is very similar to the IR-only retrieval below 1.5 km. However, including the partial profile of water vapor observed by the DIAL increases the information content in the combined IR + DIAL and MW + DIAL water vapor retrievals substantially, with the exact impact vertically depending on the characteristics of the DIAL instrument itself. Furthermore, there is a slight increase in the information content in the retrieved temperature profile using the IR + DIAL relative to the IR-only; this was not observed in the MW + DIAL retrieval.

Observed Boundary Layer Controls on Shallow Cumulus at the ARM Southern Great Plains Site

2018 ◽  
Vol 75 (7) ◽  
pp. 2235-2255 ◽  
Author(s):  
Neil P. Lareau ◽  
Yunyan Zhang ◽  
Stephen A. Klein
Keyword(s):  
Boundary Layer ◽  
Great Plains ◽  
Vertical Velocity ◽  
Mass Flux ◽  
Cloud Base ◽  
Liquid Water Path ◽  
Southern Great Plains ◽  
Clear Sky ◽  
Shallow Cumulus ◽  
In Situ Sensors

Abstract The boundary layer controls on shallow cumulus (ShCu) convection are examined using a suite of remote and in situ sensors at ARM Southern Great Plains (SGP). A key instrument in the study is a Doppler lidar that measures vertical velocity in the CBL and along cloud base. Using a sample of 138 ShCu days, the composite structure of the ShCu CBL is examined, revealing increased vertical velocity (VV) variance during periods of medium cloud cover and higher VV skewness on ShCu days than on clear-sky days. The subcloud circulations of 1791 individual cumuli are also examined. From these data, we show that cloud-base updrafts, normalized by convective velocity, vary as a function of updraft width normalized by CBL depth. It is also found that 63% of clouds have positive cloud-base mass flux and are linked to coherent updrafts extending over the depth of the CBL. In contrast, negative mass flux clouds lack coherent subcloud updrafts. Both sets of clouds possess narrow downdrafts extending from the cloud edges into the subcloud layer. These downdrafts are also present adjacent to cloud-free updrafts, suggesting they are mechanical in origin. The cloud-base updraft data are subsequently combined with observations of convective inhibition to form dimensionless “cloud inhibition” (CI) parameters. Updraft fraction and liquid water path are shown to vary inversely with CI, a finding consistent with CIN-based closures used in convective parameterizations. However, we also demonstrate a limited link between CBL vertical velocity variance and cloud-base updrafts, suggesting that additional factors, including updraft width, are necessary predictors for cloud-base updrafts.

scholarly journals THOR—Cloud Thickness from Offbeam Lidar Returns

2005 ◽  
Vol 22 (6) ◽  
pp. 605-627 ◽  
Author(s):  
Robert F. Cahalan ◽  
Matthew McGill ◽  
John Kolasinski ◽  
Tamás Várnai ◽  
Ken Yetzer
Keyword(s):  
Great Plains ◽  
Detection System ◽  
Skin Depth ◽  
Field Of View ◽  
Wide Angle ◽  
Southern Great Plains ◽  
Diffuse Halo ◽  
Atmospheric Radiation Measurement ◽  
Cloud Thickness ◽  
Physical Thickness

Abstract Conventional wisdom is that lidar pulses do not significantly penetrate clouds having an optical thickness exceeding about τ = 2, and that no returns are detectible from more than a shallow skin depth. Yet optically thicker clouds of τ ≫ 2 reflect a larger fraction of visible photons and account for much of the earth’s global average albedo. As cloud-layer thickness grows, an increasing fraction of reflected photons are scattered multiple times within the cloud and return from a diffuse concentric halo that grows around the incident pulse, increasing in horizontal area with layer physical thickness. The reflected halo is largely undetected by narrow field-of-view (FOV) receivers commonly used in lidar applications. Cloud Thickness from Offbeam Returns (THOR) is an airborne wide-angle detection system with multiple FOVs, capable of observing the diffuse halo as a wide-angle signal, from which the physical thickness of optically thick clouds can be retrieved. This paper describes the THOR system, demonstrates that the halo signal is stronger for thicker clouds, and presents a validation of physical thickness retrievals for clouds having τ > 20, from NASA’s P-3B flights over the Department of Energy’s Atmospheric Radiation Measurement Southern Great Plains site, using the lidar, radar, and other ancillary ground-based data.

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