scholarly journals Trade Wind Cloud Evolution Observed by Polarization Radar: Relationship to Giant Condensation Nuclei Concentrations and Cloud Organization

2011 ◽  
Vol 68 (5) ◽  
pp. 1075-1096 ◽  
Author(s):  
Hilary A. Minor ◽  
Robert M. Rauber ◽  
Sabine Göke ◽  
Larry Di Girolamo
Keyword(s):  
Doppler Radar ◽  
Cloud Base ◽  
Trade Wind ◽  
High Threshold ◽  
Threshold Values ◽  
Condensation Nuclei ◽  
Horizontal Polarization ◽  
Shallow Marine ◽  
Rain Drop ◽  
Differential Reflectivity

Abstract Shallow marine trade wind cumuli are one of the most prevalent cloud types in the tropical atmosphere. Understanding how precipitation forms within these clouds is necessary to advance our knowledge concerning their role in climate. This paper presents a statistical analysis of the characteristic heights and times at which precipitation in trade wind clouds passes through distinct stages in its evolution as defined by the equivalent radar reflectivity factor at horizontal polarization ZH, the differential reflectivity ZDR, and the spatial correlation between and averages of these variables. The data were obtained during the Rain in Cumulus over the Ocean (RICO) field campaign by the National Center for Atmospheric Research (NCAR) S-band dual-polarization (S-Pol) Doppler radar, the National Science Foundation (NSF)–NCAR C130 aircraft, and soundings launched near the radar. The data consisted of 76 trade cumuli that were tracked from early echo development through rainout on six days during RICO. Trade wind clouds used in the statistical analyses were segregated based on giant condensation nuclei (GCN) measurements made during low-level aircraft flight legs on the six days. This study found that the rate of precipitation formation in shallow marine cumulus was unrelated to the GCN concentration in the ambient environment. Instead, the rate at which precipitation developed in the clouds appeared to be related to the mesoscale forcing as suggested by the cloud organization. Although GCN had no influence on the rate of precipitation development, the data suggest that they do contribute to a modification of the rain drop size distribution within the clouds. With very few exceptions, high threshold values of ZDR were found well above cloud base on days with high GCN concentrations. On the days that were exceptions, these threshold values were almost always achieved near cloud base.

Measuring the variability of the shallow convective mass flux profiles in the tropical trade wind region

2020 ◽  
Author(s):  
Marcus Klingebiel ◽  
Heike Konow ◽  
Bjorn Stevens
Keyword(s):  
Boundary Layer ◽  
Vertical Velocity ◽  
Mass Flux ◽  
Doppler Radar ◽  
Cloud Fraction ◽  
Cloud Base ◽  
Trade Wind ◽  
Geophysical Research ◽  
Wind Region ◽  
Convective Mass Flux

<p>Mass flux is a key parameter to represent shallow convection in global circulation models. To estimate the shallow convective mass flux as accurately as possible, observations of this parameter are necessary. Prior studies from Ghate et al. (2011) and Lamer et al. (2015) used Doppler radar measurements over a few months to identify a typical shallow convective mass flux profile based on cloud fraction and vertical velocity. In this study, we extend their observations by using long term remote sensing measurements at the Barbados Cloud Observatory (13° 09’ N, 59° 25’ W) over a time period of 30 months and check a hypothesis by Grant (2001), who proposed that the cloud base mass flux is just proportional to the sub-cloud convective velocity scale. Therefore, we analyze Doppler radar and Doppler lidar measurements to identify the variation of the vertical velocity in the cloud and sub-cloud layer, respectively. Furthermore, we show that the in-cloud mass flux is mainly influenced by the cloud fraction and provide a linear equation, which can be used to roughly calculate the mass flux in the trade wind region based on the cloud fraction.</p><p> </p><p>References:<br>Ghate,  V.  P.,  M.  A.  Miller,  and  L.  DiPretore,  2011:   Vertical  velocity structure of marine boundary layer trade wind cumulus clouds. Journal  of  Geophysical  Research: Atmospheres, 116  (D16), doi:10.1029/2010JD015344.</p><p>Grant,  A.  L.  M.,  2001:   Cloud-base  fluxes  in  the  cumulus-capped boundary layer. Quarterly Journal of the Royal Meteorological Society, 127 (572), 407–421, doi:10.1002/qj.49712757209.</p><p>Lamer, K., P. Kollias, and L. Nuijens, 2015:  Observations of the variability  of  shallow  trade  wind  cumulus  cloudiness  and  mass  flux. Journal of Geophysical Research: Atmospheres, 120  (12), 6161–6178, doi:10.1002/2014JD022950.</p>

scholarly journals Experimental Quantification of the Sampling Uncertainty Associated with Measurements from PARSIVEL Disdrometers

2011 ◽  
Vol 12 (3) ◽  
pp. 352-370 ◽  
Author(s):  
Joël Jaffrain ◽  
Alexis Berne
Keyword(s):  
Temporal Resolution ◽  
Total Concentration ◽  
Intrinsic Property ◽  
Ground Level ◽  
Relevant Information ◽  
Horizontal Polarization ◽  
Sampling Uncertainty ◽  
Median Volume ◽  
Rain Drop ◽  
Differential Reflectivity

Abstract The variability of the (rain)drop size distribution (DSD) in time and space is an intrinsic property of rainfall, which is of primary importance for various environmental fields such as remote sensing of precipitation, for example. DSD observations are usually collected using disdrometers deployed at the ground level. Like any other measurement of a physical process, disdrometer measurements are affected by noise and sampling effects. This uncertainty must be quantified and taken into account in further analyses. This paper addresses this issue for the Particle Size Velocity (PARSIVEL) optical disdrometer by using a large dataset corresponding to light and moderate rainfall and collected from two collocated PARSIVELs deployed during 15 months in Lausanne, Switzerland. The relative sampling uncertainty associated with quantities characterizing the DSD—namely the total concentration of drops Nt and the median-volume diameter D0—is quantified for different temporal resolutions. Similarly, the relative sampling uncertainty associated with the estimates of the most commonly used weighted moments of the DSD (i.e., the rain-rate R, the radar reflectivity at horizontal polarization Zh, and the differential reflectivity Zdr) is quantified as well for different weather radar frequencies. The relative sampling uncertainty associated with estimates of Nt is below 13% for time steps longer than 60 s. For D0, it is below 8% for D0 values smaller than 1 mm. The associated sampling uncertainty for estimates of R is on the order of 15% at a temporal resolution of 60 s. For Zh, the sampling uncertainty is below 9% for Zh values below 35 dBZ at a temporal resolution of 60 s. For Zdr values below 0.75 dB, the sampling uncertainty is below 36% for all temporal resolutions. These analyses provide relevant information for the accurate quantification of the variability of the DSD from disdrometer measurements.

Measuring shallow convective mass flux profiles in the trade wind region

2021 ◽  
Author(s):  
Marcus Klingebiel ◽  
Heike Konow ◽  
Bjorn Stevens
Keyword(s):  
Mass Flux ◽  
Large Scale ◽  
Doppler Radar ◽  
Cloud Base ◽  
Trade Wind ◽  
Doppler Lidar ◽  
Shallow Convection ◽  
Lidar Measurements ◽  
Flux Profile ◽  
Convective Mass Flux

AbstractMass flux is a key quantity in parameterizations of shallow convection. To estimate the shallow convective mass flux as accurately as possible, and to test these parameterizations, observations of this parameter are necessary. In this study, we show how much the mass flux varies and how this can be used to test factors that may be responsible for its variation. Therefore, we analyze long term Doppler radar and Doppler lidar measurements at the Barbados Cloud Observatory over a time period of 30 months, which results in a mean mass flux profile with a peak value of 0.03 kg m−2 s−1 at an altitude of ~730 m, similar to observations from Ghate et al. (2011) at the Azores Islands. By combining Doppler radar and Doppler lidar measurements, we find that the cloud base mass flux depends mainly on the cloud fraction and refutes an idea based on large eddy simulations, that the velocity scale is in major control of the shallow cumulus mass flux. This indicates that the large scale conditions might play a more important role than what one would deduce from simulations using prescribed large-scale forcings.

scholarly journals Improving Polarimetric C-Band Radar Rainfall Estimation with Two-Dimensional Video Disdrometer Observations in Eastern China

2017 ◽  
Vol 18 (5) ◽  
pp. 1375-1391 ◽  
Author(s):  
Gang Chen ◽  
Kun Zhao ◽  
Guifu Zhang ◽  
Hao Huang ◽  
Su Liu ◽  
...  
Keyword(s):  
Doppler Radar ◽  
Eastern China ◽  
Summer Precipitation ◽  
Summer Rainfall ◽  
Squall Line ◽  
Two Dimensional ◽  
Horizontal Polarization ◽  
Radar Rainfall ◽  
Convective Systems ◽  
Differential Reflectivity

Abstract In this study, the capability of using a C-band polarimetric Doppler radar and a two-dimensional video disdrometer (2DVD) to estimate monsoon-influenced summer rainfall during the Observation, Prediction and Analysis of Severe Convection of China (OPACC) field campaign in 2014 and 2015 in eastern China is investigated. Three different rainfall R estimators, for reflectivity at horizontal polarization [R(Zh)], for reflectivity at horizontal polarization and differential reflectivity factor [R(Zh, Zdr)], and for specific differential phase [R(KDP)], are derived from 2-yr 2DVD observations of summer precipitation systems. The radar-estimated rainfall is compared to gauge observations from eight rainfall episodes. Results show that the two polarimetric estimators, R(Zh, Zdr) and R(KDP), perform better than the traditional Zh–R relation [i.e., R(Zh)]. The KDP-based estimator [i.e., R(KDP)] produces the best rainfall accumulations. The radar rainfall estimators perform differently across the three organized convective systems (mei-yu rainband, typhoon rainband, and squall line). Estimator R(Zh) overestimates rainfall in the mei-yu rainband and squall line, and R(Zh, Zdr) mitigates the overestimation in the mei-yu rainband but has a large bias in the squall line. QPE from R(KDP) is the most accurate among the three estimators, but it possesses a relatively large bias for the squall line compared to the mei-yu case. The high variability of drop size distribution (DSD) related to the precipitation microphysics in different types of rain is largely responsible for the case-dependent QPE performance using any single radar rainfall estimator. The squall line has a distinct ice-phase process with a large mean size of raindrops, while the mei-yu rainband and typhoon rainband are composed of smaller raindrops. Based on the statistical QPE error in the ZH–ZDR space, a new composite rainfall estimator is constructed by combining R(Zh), R(Zh, Zdr), and R(KDP) and is proven to outperform any single rainfall estimator.

Microphysical Insights into Ice Pellet Formation Revealed by Fully Polarimetric Ka-Band Doppler Radar

2020 ◽  
Vol 59 (10) ◽  
pp. 1557-1580
Author(s):  
Matthew R. Kumjian ◽  
Dana M. Tobin ◽  
Mariko Oue ◽  
Pavlos Kollias
Keyword(s):  
New York ◽  
Correlation Coefficient ◽  
Doppler Radar ◽  
Radar Data ◽  
Ice Crystals ◽  
Horizontal Polarization ◽  
Ka Band ◽  
Pellet Formation ◽  
Linear Depolarization Ratio ◽  
Differential Reflectivity

AbstractFully polarimetric scanning and vertically pointing Doppler spectral data from the state-of-the-art Stony Brook University Ka-band Scanning Polarimetric Radar (KASPR) are analyzed for a long-duration case of ice pellets over central Long Island in New York from 12 February 2019. Throughout the period of ice pellets, a classic refreezing signature was present, consisting of a secondary enhancement of differential reflectivity ZDR beneath the melting layer within a region of decreasing reflectivity factor at horizontal polarization ZH and reduced copolar correlation coefficient ρhv. The KASPR radar data allow for evaluation of previously proposed hypotheses to explain the refreezing signature. It is found that, upon entering a layer of locally generated columnar ice crystals and undergoing contact nucleation, smaller raindrops preferentially refreeze into ice pellets prior to the complete freezing of larger drops. Refreezing particles exhibit deformations in shape during freezing, leading to reduced ρhv, reduced co-to-cross-polar correlation coefficient ρxh, and enhanced linear depolarization ratio, but these shape changes do not explain the ZDR signature. The presence of columnar ice crystals, though apparently crucial for instigating the refreezing process, does not contribute enough backscattered power to affect the ZDR signature, either.

scholarly journals A New Three-Dimensional Visualization System for Combining Aircraft and Radar Data and Its Application to RICO Observations

2010 ◽  
Vol 27 (5) ◽  
pp. 811-828 ◽  
Author(s):  
Dan K. Arthur ◽  
Sonia Lasher-Trapp ◽  
Ayman Abdel-Haleem ◽  
Nicholas Klosterman ◽  
David S. Ebert
Keyword(s):  
3D Visualization ◽  
Temporal Trends ◽  
Three Dimensional ◽  
Spatial Location ◽  
Research Problem ◽  
Radar Data ◽  
Cloud Base ◽  
Trade Wind ◽  
Visualization System ◽  
Differential Reflectivity

Abstract The analysis of diverse datasets from meteorological field campaigns often involves the use of separate 1D or combined 2D plots from various applications, making the determination of spatial and temporal relationships and correlations among these data, and the overall synthesis of information, extremely challenging. Presented here is a new 3D visualization tool, the Aircraft and Radar Data Collocation and Analysis in 3D (ARCA3D), that can combine data collected from different sources and at different scales, utilizing advanced visualization and user interface techniques, which allows for easier comparison and synthesis of such disparate data. The 3D tool is demonstrated with aircraft-based microphysical probe data and ground-based dual-polarization radar data all collected during the Rain in Cumulus over the Ocean (RICO) field campaign. The 3D volumes of radar data can be interactively selected and quantitatively probed, while aircraft-measured variables can be viewed along the aircraft track plotted within the 3D radar volumes or plotted as time series within regions of interest relative to the radar echoes. The greatest benefits of the new software, the 3D viewing of large radar and aircraft datasets with user-driven controls, are difficult to communicate here in a static, 2D written medium, but the application of the tool toward a research problem is presented to elucidate the impacts of these benefits. The ARCA3D software is used to investigate the possible role of giant aerosol particles in the development of precipitation in trade wind cumuli. The temporal trends in the spatial location of the maximum differential reflectivity echoes within the clouds are examined with respect to the ambient giant aerosol number concentration and the measured cloud-base droplet number concentrations on 10 days. The results indicate that in trade wind cumuli of sufficient depth, giant aerosol may determine the original location of the earliest differential reflectivity maximum echo, and thus the first raindrops when present in higher number concentrations. However, when the giant aerosol are less plentiful, the number of cloud droplets activated above the cloud base may also play a role in determining the location of the earliest maximum differential reflectivity echo, and thus the earliest raindrops, in these trade wind cumuli.

scholarly journals Biogeography of Tropical Montane Cloud Forests. Part II: Mapping of Orographic Cloud Immersion

2008 ◽  
Vol 47 (8) ◽  
pp. 2183-2197 ◽  
Author(s):  
Udaysankar S. Nair ◽  
Salvi Asefi ◽  
Ronald M. Welch ◽  
D. K. Ray ◽  
Robert O. Lawton ◽  
...  
Keyword(s):  
Costa Rica ◽  
Cloud Forest ◽  
United Nations Environment Programme ◽  
Cloud Base ◽  
Trade Wind ◽  
Cloud Forests ◽  
Study Region ◽  
Modis Data ◽  
Monitoring Centre ◽  
Tropical Montane Cloud Forests

Abstract This study details two unique methods to quantify cloud-immersion statistics for tropical montane cloud forests (TMCFs). The first technique uses a new algorithm for determining cloud-base height using Moderate Resolution Imaging Spectroradiometer (MODIS) cloud products, and the second method uses numerical atmospheric simulation along with geostationary satellite data. Cloud-immersion statistics are determined using MODIS data for March 2003 over the study region consisting of Costa Rica, southern Nicaragua, and northern Panama. Comparison with known locations of cloud forests in northern Costa Rica shows that the MODIS-derived cloud-immersion maps successfully identify known cloud-forest locations in the United Nations Environment Programme (UNEP) World Conservation Monitoring Centre (WCMC) database. Large connected regions of cloud immersion are observed in regions in which the trade wind flow is directly impinging upon the mountain slopes; in areas in which the flow is parallel to the slopes, a fractured spatial distribution of TMCFs is observed. Comparisons of the MODIS-derived cloud-immersion map with the model output show that the MODIS product successfully captures the important cloud-immersion patterns in the Monteverde region of Costa Rica. The areal extent of cloud immersion is at a maximum during morning hours and at a minimum during the afternoon, before increasing again in the evening. Cloud-immersion frequencies generally increase with increasing elevation and tend to be higher on the Caribbean Sea side of the mountains. This study shows that the MODIS data may be used successfully to map the biogeography of cloud forests and to quantify cloud immersion over cloud-forest locations.

scholarly journals Differences between Nonprecipitating Tropical and Trade Wind Marine Shallow Cumuli

2016 ◽  
Vol 144 (2) ◽  
pp. 681-701 ◽  
Author(s):  
Virendra P. Ghate ◽  
Mark A. Miller ◽  
Ping Zhu
Keyword(s):  
Surface Fluxes ◽  
Cloud Base ◽  
Trade Wind ◽  
Cumulus Clouds ◽  
Wind Speeds ◽  
Lower Cloud ◽  
Observational Site ◽  
Velocity Scale ◽  
Atmospheric Radiation Measurement ◽  
The Mean

Abstract Marine nonprecipitating cumulus topped boundary layers (CTBLs) observed in a tropical and in a trade wind region are contrasted based on their cloud macrophysical, dynamical, and radiative structures. Data from the Atmospheric Radiation Measurement (ARM) observational site previously operating at Manus Island, Papua New Guinea, and data collected during the deployment of ARM Mobile Facility at the island of Graciosa, in the Azores, were used in this study. The tropical marine CTBLs were deeper, had higher surface fluxes and boundary layer radiative cooling, but lower wind speeds compared to their trade wind counterparts. The radiative velocity scale was 50%–70% of the surface convective velocity scale at both locations, highlighting the prominent role played by radiation in maintaining turbulence in marine CTBLs. Despite greater thicknesses, the chord lengths of tropical cumuli were on average lower than those of trade wind cumuli, and as a result of lower cloud cover, the hourly averaged (cloudy and clear) liquid water paths of tropical cumuli were lower than the trade wind cumuli. At both locations ~70% of the cloudy profiles were updrafts, while the average amount of updrafts near cloud base stronger than 1 m s−1 was ~22% in tropical cumuli and ~12% in the trade wind cumuli. The mean in-cloud radar reflectivity within updrafts and mean updraft velocity was higher in tropical cumuli than the trade wind cumuli. Despite stronger vertical velocities and a higher number of strong updrafts, due to lower cloud fraction, the updraft mass flux was lower in the tropical cumuli compared to the trade wind cumuli. The observations suggest that the tropical and trade wind marine cumulus clouds differ significantly in their macrophysical and dynamical structures.

scholarly journals Improved rain-rate and drop-size retrievals from airborne and spaceborne Doppler radar

2017 ◽  
Author(s):  
Shannon L. Mason ◽  
J. Christine Chiu ◽  
Robin J. Hogan ◽  
Lin Tian
Keyword(s):  
Size Distribution ◽  
Drop Size ◽  
Rain Rate ◽  
Doppler Radar ◽  
Number Concentration ◽  
Doppler Velocity ◽  
Light Rain ◽  
Warm Rain ◽  
Rain Drop ◽  
Drop Number

Abstract. Satellite radar remote-sensing of rain is important for quantifying of the global hydrological cycle, atmospheric energy budget, and many microphysical cloud and precipitation processes; however, radar estimates of rain rate are sensitive to assumptions about the raindrop size distribution. The upcoming EarthCARE satellite will feature a 94-GHz Doppler radar alongside lidar and radiometer instruments, presenting opportunities for enhanced global retrievals of the rain drop size distribution. In this paper we demonstrate the capability to retrieve both rain rate and a parameter of the rain drop size distribution from an airborne 94-GHz Doppler radar using CAPTIVATE, the variational retrieval algorithm developed for EarthCARE radar–lidar synergy. For a range of rain regimes observed during the Tropical Composition, Cloud and Climate Coupling (TC4) field campaign in the eastern Pacific in 2007, we explore the contributions of Doppler velocity and path-integrated attenuation (PIA) to the retrievals, and evaluate the retrievals against independent measurements from a second, less attenuated, Doppler radar aboard the same aircraft. Retrieved drop number concentration varied over five orders of magnitude between light rain from melting ice, and warm rain from liquid clouds. Doppler velocity can be used to estimate rain rate over land, and retrievals of rain rate and drop number concentration are possible in profiles of light rain over land; in moderate warm rain, drop number concentration can be retrieved without Doppler velocity. These results suggest that EarthCARE rain retrievals facilitated by Doppler radar will make substantial improvements to the global understanding of the interaction of clouds and precipitation.

Control Strategies for Multistage Solar Collector Systems

1988 ◽  
Vol 110 (3) ◽  
pp. 230-232
Author(s):  
C. Saltiel
Keyword(s):  
Comparative Study ◽  
Flow Control ◽  
Numerical Simulations ◽  
Control Strategy ◽  
System Performance ◽  
Solar Collector ◽  
Control Strategies ◽  
Climatic Conditions ◽  
High Threshold ◽  
Threshold Values

A comparative study of the yearly performance of multistage solar collector systems, (comprised of more than one collector type) with a single on/off flow control strategy for all the collectors and separate on/off controls for each collector stage, is performed. Detailed numerical simulations under a range of climatic conditions showed that there is little advantage in using individual collector controls over a single on/off control strategy when the systems operate at low collector thresholds, but differences in system performance can be quite significant at high threshold values. In addition, the choice of the single control strategy (i.e., which collector the strategy is based on) at low thresholds is not critical in terms of system performance.

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