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Abstract Shear and buoyancy gradients, often observed in midlatitude baroclinic and orographic winter storms, produce discrete layers of turbulence. These turbulent layers modify the distribution of supercooled liquid water (SLW), whose presence enables hydrometeors to grow to precipitation sizes faster than through vapor-ice deposition alone. Both the Wegener–Bergeron–Findeisen process and riming require SLW—heterogeneously distributed in response to the dynamic forcings at all superposed scales. The University of Wyoming W-band cloud radar Doppler spectrum width characterizes the air motion turbulence intensity in mixed-phase layer clouds after avoiding fall speed dominated regions through comparison to coarser radar turbulence metrics. Embedded layers of turbulent air motion are compared to quiescent cloud regions in either/both the upwind and downwind directions. Median radar reflectivity profiles characterize the vertical growth of hydrometeors in the vicinity of identified layers, and differences in these vertical reflectivity gradients comparing turbulent to nonturbulent regions quantify enhanced hydrometeor growth over the layer. Over the entirety of the Seeded and Natural Orographic Wintertime Clouds—the Idaho Experiment, this parameter demonstrates a statistically significant increase, −13.6 dBZekm−1(from −1.7 to −24.5, 95% computed confidence), in radar reflectivity echo power with distance downward for embedded turbulent layers compared to quiescent cloud nearby. The increased vertical particle growth rate for turbulent layers appears to result from spatially heterogeneous phase partitioning, increased SLW mass and extent, and enhanced collision/collection rates in these layers. These first two conditions are examined individually where turbulent layers or fall streaks are sampled in situ, while the latter agrees with modeling results but can only be inferred herein. Significance StatementTurbulent mixing in mixed-phase clouds is understood to enhance cloud hydrometeor growth. This study quantifies these effects on observed airborne W-band radar reflectivity over an entire field campaign targeting midlatitude winter storms and calls into question whether this linkage is diagnosed properly if at all in forecast and bulk microphysical models with coarse (greater than 500 m) grid spacing or vertical resolution.
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Stratocumulus Precipitation Properties Over the Southern Ocean Observed From Aircraft During the SOCRATES Campaign
Abstract Precipitation plays an important role in cloud and aerosol processes over the Southern Ocean (SO). The main objective of this study is to characterize SO precipitation properties associated with SO stratocumulus clouds. We use data from the Southern Ocean Clouds Radiation Aerosol Transport Experimental Study (SOCRATES), and leverage observations from airborne radar, lidar, and in situ probes. We find that for the cold‐topped clouds (cloud‐top‐temperature <0°C), the phase of precipitation with reflectivity >0 dBZ is predominantly ice, while reflectivity < −10 dBZ is predominantly liquid. Liquid‐phase precipitation properties are retrieved where radar and lidar are zenith‐pointing. Power‐law relationships between reflectivity (Z) and rain rate (R) are developed, and the derived Z–R relationships show vertical dependence and sensitivity to the presence of droplets with diameters between 10 and 40 μm. Using derived Z–R relationships, a reflectivity‐velocity (ZV) retrieval method, and a radar‐lidar retrieval method, we derive rain rate and other precipitation properties. The retrieved rain rate from all three methods shows good agreement with in‐situ aircraft estimates, with rain rates typically being quite light (<0.1 mm hr−1). We examine the vertical distribution of precipitation properties, and find that rain rate, precipitation number concentration, and precipitation liquid water all decrease as one gets closer to the surface, while precipitation size and distribution width increases. We also examine how cloud base rain rate (RCB) depends on cloud depth (H) and aerosol concentration (Na) for particles with a diameter greater than 70 nm, and find thatRCBis proportional to .
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- Award ID(s):
- 2124993
- PAR ID:
- 10522912
- Publisher / Repository:
- Journal of Geophysical Research: Atmospheres
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 129
- Issue:
- 6
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Recent studies from the Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment (SNOWIE) demonstrated definitive radar evidence of seeding signatures in winter orographic clouds during three intensive operation periods (IOPs) where the background signal from natural precipitation was weak and a radar signal attributable to seeding could be identified as traceable seeding lines. Except for the three IOPs where seeding was detected, background natural snowfall was present during seeding operations and no clear seeding signatures were detected. This paper provides a quantitative analysis to assess if orographic cloud seeding effects are detectable using radar when background precipitation is present. We show that a 5-dB change in equivalent reflectivity factorZeis required to stand out against background naturalZevariability. This analysis considers four radar wavelengths, a range of background ice water contents (IWC) from 0.012 to 1.214 g m−3, and additional IWC introduced by seeding ranging from 0.012 to 0.486 g m−3. The upper-limit values of seeded IWC are based on measurements of IWC from the Nevzorov probe employed on the University of Wyoming King Air aircraft during SNOWIE. This analysis implies that seeding effects will be undetectable using radar within background snowfall unless the background IWC is small, and the seeding effects are large. It therefore remains uncertain whether seeding had no effect on cloud microstructure, and therefore produced no signature on radar, or whether seeding did have an effect, but that effect was undetectable against the background reflectivity associated with naturally produced precipitation. Significance StatementOperational glaciogenic seeding programs targeting wintertime orographic clouds are funded by a range of stakeholders to increase snowpack. Glaciogenic seeding signatures have been observed by radar when natural background snowfall is weak but never when heavy background precipitation was present. This analysis quantitatively shows that seeding effects will be undetectable using radar reflectivity under conditions of background snowfall unless the background snowfall is weak, and the seeding effects are large. It therefore remains uncertain whether seeding had no effect on cloud microstructure, and therefore produced no signature on radar, or whether seeding did have an effect, but that effect was undetectable against the background reflectivity associated with naturally produced precipitation. Alternative assessment methods such as trace element analysis in snow, aircraft measurements, precipitation measurements, and modeling should be used to determine the efficacy of orographic cloud seeding when heavy background precipitation is present.more » « less
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2023JD039831
