Anvil microphysical signatures associated with lightning-produced NO<sub><i>x</i></sub>

Abstract

Abstract. Thunderstorm anvils were studied during the Deep Convective Clouds and Chemistry experiment (DC3), using in situ measurements and observations of ice particles and NOx together with radar and lightning mapping array measurements. A characteristic ice particle and NOx signature was found in the anvils from three storms, each containing high lightning flash rates in the storm core prior to anvil sampling. This signature exhibits high concentrations of frozen droplets (as measured by a Cloud Droplet Probe) coincident with lower NOx on the edges of the anvil. The central portion of these anvils exhibited a high degree of aggregation of these frozen droplets and higher levels of NOx. In contrast, a deep convective cell with low lightning flash rates had high concentrations of frozen droplets in its anvil's central region. A conceptual model for these results is presented. The abundance of frozen drop (chain) aggregates vs. individual frozen droplets in the central anvil region of the strong thunderstorms that were studied appears to be related to the degree of electrification (marked by increased lightning flash rates). Accordingly, the highest NOx concentrations coexist with regions where the most aggregation of frozen droplets has occurred. These observations between anvil microphysics and lightning/NOx signatures suggest that lightning data may be an important tool to characterize or infer the microphysical, radiative and chemical properties of thunderstorm anvils.

Electrification in Mesoscale Updrafts of Deep Stratiform and Anvil Clouds in Florida

“…The laboratory studies of Saunders and Wahab () and Wahab () showed that in a vertical electric field (i.e., the field was aligned with the direction of fall) a threshold of ice crystal concentration of 250/L and an electric field threshold of ~60 kV/m was required in order to enhance aggregation. In another study Stith et al () have observed chain‐like aggregation of frozen cloud droplets in the upper parts of some anvils in association with high values of NO x in which lightning was known to have occurred. They attributed the aggregation of frozen droplets to electric field forces.…”

A Review of Ice Particle Shapes in Cirrus formed In Situ and in Anvils

“…On the other hand, small cloud droplets are often transported up to the homogeneous freezing level in strong updrafts formed in midlatitude continental convection (Lawson et al, ; Rosenfeld & Woodley, ). The high concentrations of small droplets in the updrafts either can participate in riming or, after homogeneous freezing, can form aggregates (e.g., Stith et al, , ). Anvils generally form at temperatures colder than −38 °C, so all supercooled liquid water is frozen and the ice rapidly depletes the supersaturated fraction of water vapor in the anvil, driving RH ice down to 100% (Diao et al, ; Jensen et al, ), which inhibits formation and growth of polycrystals and rosettes (Bailey & Hallett, ).…”

Introduction to the Deep Convective Clouds and Chemistry (DC3) 2012 Studies

“…Analyses of cloud physical properties were conducted using aircraft measurements of cloud particle size distributions (Stith et al, ) and water vapor (Diao et al, ), as well as balloon‐borne video disdrometer (Waugh et al, ). The recently developed balloon‐borne microphysics probe can provide observations at fine scales and give calculated cloud particle mixing ratios and reflectivity in agreement with radar and cloud‐resolving, kinematic model results.…”

“…The frozen drop aggregates are formed by electrical forces associated with high electric fields accompanying lightning. Since lightning is also the source of lightning‐NO x , these studies suggested that electrically active storms may have characteristically different ice particle types in the anvil compared to less electrically active storms, which may have an impact on the radiative impacts of the anvil clouds (Stith et al, ).…”