1. INTRODUCTION:
The COnvective Precipitation Experiment (COPE) was an international, UK led field campaign un-
dertaken during July and August 2013 commissioned to improve Quantitative Precipitation Forecasts
(QPF) for summertime convection over SW England, a region prone to flash flooding (Leon et al.
2015).
The COnvective Precipitation Experiment – Microphysics and Entrainment Dependencies (COPE-
MED) project was a key component of COPE that seeks to answer two fundamental hypothothes:
I. The formation of raindrops through the warm rain process is critical to the development
of heavy precipitation at the surface, even when ice processes are active.
II. The effects of entrainment must be mitigated by some factors in order to produce heavy
precipitation at the surface.
This research is split into three indirectly connected sections:
1. A liquid water content (LWC) measurement by in-situ probe comparison.
2. A survey of LWC observed during COPE.
3. An analysis of the observed droplet spectra biomodality from select low-precipitation penetrations during COPE.
A Survey of the Measured Cloud Liquid Water Content and an Analysis of the Droplet Spectra Observed During the Summer 2013 COPE-MED Field Campaign
Jason A. Sulskis, Jeffery R. French, and David C. Leon
Department of Atmospheric Science, College of Engineering and Applied Science, The University of Wyoming
Laramie, WY 82071
jsulskis@uwyo.edu
1. IN-SITU LWC PROBE COMPARISONS:
Derived LWC from the Cloud Droplet Probe (CDP) was compared to to:
• LWC Measured by the DMT LWC-100 “hotwire” probe
• LWC Measured by the Nevzorov LWC probe
• LWC Measured by the Gerber PVM-100A optical scattering probe
A general M-estimator method (Huber 1964) that ignores outliers was used for regression
analysis.
LWC2
= slope × LWC1,
with the slope’s departure from the 1:1 line giving the % differences.
Scatterplots from the comparisons by RF for July 10th and 29th as well as August 2nd and 15th:
Percent differences of each probe compared to the CDP from all segregations:
• The hotwire probe measured, on average, within 20% of the CDP.
• The Hotwire probe showed the most scatter and was biased toward higher values of LWC compared to the CDP.
• The Nevzorov LWC probe measured within ~ 10% of the CDP and didn’t show a consistent high/low bias in the measurements of LWC.
• The PVM’s measured LWC ranged from between -16% and 30% of the CDP.
• The PVM had the largest standard deviation of percent differences and showed a bias toward the larger values of LWC consistently overestimating LWC compared
to the CDP where the overestimate seems to increase with increasing number concentration (and decreasing mean droplet diameter).
• Precipitation concentration doesn’t seem to have a statistically significant impact on the measured LWC for any of the probes compared.
• Precipitation effects may or may not be due to particle size impacts.
REFERENCES:
Huber, P. J. (1964): ‘Robust Estimation of a Location Parameter’. Ann. Math. Statist., 1, 73-101.
Jackson, R. C. et al. (2015): ‘The Dependence Of Cirrus Gamma Size Distributions Expressed As Volumes In N0
-l-m Phase Space And Bulk Cloud Properties On Environmental Conditions: Results From The Small Ice Particles In Cirrus Experiment (SPARTICUS).’, J. Geophys. Res. Atmos., in press.
Korolev, A. V., and Mazin, I.P. (2003): ‘Supersaturation Of Water Vapor In Clouds’. J. Atmos. Sci. 60(24), 2957-2974.
Leon, D. C. et al. (2015): ‘The Convective Precipitation Experiment (COPE): Investigating The Origins Of Heavy Precipitation In The Southwestern UK’. Bull. Amer. Meteor. Soc., in press.
Paluch, I. R., and Knight, C.A. (1984): ‘Mixing And The Evolution Of Cloud Droplet Size Spectra In A Vigorous Continental Cumulus’. J. Atmos. Sci., 41(11) 1801-1815.
2. IN-SITU LWC SURVEY:
• Vertical profiles of the measured LWC from all of the cloud penetrations on a giv-
en research flight are plotted in 100m vertical intervals.
• Minimum value, maximum value, median value, 25% quartile, and 75% quartile
of LWC are shown on standard “box & whisker” plots.
• The adiabatic LWC (ALWC) is calculated from first-principles using data from the
UWKAfrom no-precipitation penetrations near cloud base (shown as solid curve).
• Vertical profiles plotted against GPS altitude and temperature data taken from the
UWKA.
3. SPECTRAL BIMODALITY ANALYSIS:
Criteria:
• A subset of droplet spectra, that had reasonable amounts of LWC and little or no precipitation.
• Two specific research flight days chosen: August 2, 2013 and July 10, 2013 due to their overall low precipitation characteristics.
Methodology:
• Mode edge locations detected using an algorithm that uses a centered difference approximated derivative (Jackson et al. 2015).
• No mode edge detected to within Poisson statistics spectra is then considered to be unimodal.
• Spectral ratio: ratio of the total number concentration of the small diameter mode to the total number concentration of the larger diameter mode gives “magnitude” of the bimodality.
• Percent of Particles in small mode is calculated.
• Evidence of possible secondary activation using methodology by Paluch and Knight (1984): Supersaturation experienced if small mode population ignored.
• The theoretical supersaturation, and the updrafts required to reach a particular supersaturation value, are calculated using Korolev and Mazin (2003).
Examples from an August 2nd
& July 10th
low precipitation case of a bimodal spectra and plots of required updrafts for typical supersaturation levels:
SUMMARY:
This research was undertaken so that future COPE analysis can be put into the broader perspective of the overarching objectives of COPE and begin to answer the two main hy-
potheses of COPE-MED.
• The LWC probe comparison showed remarkably good agreement between bulk LWC probes and the CDP for all cases, however the PVM consistently overestimated LWC com-
pared to the CDP, especially as mean diameter decreased and droplet number concentration increased. Precipitation did not seem to have a statistically significant impact upon the
probe LWC comparisons.
• A LWC survey was completed with vertical statistics plotted against their adiabatic profile for use in future COPE data analysis and model parameterizations.
• Analysis of the bimodal spectra observed on low precipitation penetrations during COPE is ongoing. Although secondary activation was initially suspected as a probable cause
of the spectral bimodality, the likelihood based upon current analysis is low and the bimodality is more likely explained by some other process.
ACKNOWLEGEMENTS:
This work was supervised by Jeffrey R. French and David C. Leon, at the University of Wyoming, under NSF grant # AGS-1230203. Robert C. Jackson was indispensable in the
implantation of his mode edge detection algorithm to this work. David M. Plummer contributed many helpful suggestions, to both the research work contained herein and to the
overall design of this poster. The UK Met office and UWKA group at the University of Wyoming were instrumental in providing access to the necessary data used herein. Finally,
thanks need to be given to the rest of the observational microphysics research group and to the author’s colleagues at the University of Wyoming.
Each LWC comparison was segregated by a specific criteria:
1. Research flight (RF)
2. Range of droplet concentration
3. Range of mean droplet diameter
4. Precipitating vs. non-precipitating clouds
Comparisons were made between:
• Threshold LWC value of 0.02 g/m3
• Maximum LWC value of 1.8 g/m3