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Abstract. Understanding lightning NO x (NO + NO2) production on the cloud scale is key for developing better parameterizations of lightning NOx for use in regional and global chemical transport models. This paper attempts to further the understanding of lightning NOx production on the cloud scale using a cloud model simulation of an observed thunderstorm. Objectives are (1) to infer from the model simulations and in situ measurements the relative production rates of NOx by cloud-to-ground (CG) and intracloud (IC) lightning for the storm; (2) to assess the relative contributions in the storm anvil of convective transport of NOx from the boundary layer and NOx production by lightning; and (3) to simulate the effects of the lightning-generated NOx on subsequent photochemical ozone production. We use a two-dimensional cloud model that includes a parameterized source of lightning-generated NOx to study the production and advection of NO x associated with a developing northeast Colorado thunderstorm observed on July 12, 1996, during the Stratosphere-Troposphere Experiment--Radiation, Aerosols, Ozone

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Particle size and volume measurements obtained with the forward scattering spectrometer probe (FSSP), model 300 during January and February 1989 in the Airborne Arctic Stratospheric Experiment are presented and used to study processes important in the formation and growth of polar stratospheric cloud (PSC) particles. Comparisons of the observations with expected sulfuric acid droplet deliquescence suggest that in the Arctic a major fraction of the sulfuric acid droplets remain liquid until temperatures at least as low as 193 K. Arguments are presented to suggest that homogeneous freezing of the sulfuric acid droplets might occur near 190 K and might play a role in the formation of PSCs. The first suggestion of nitric acid trihydrate (NAT) particles appears near saturation ratios of HNO3 with respect to NAT of 1 (about 195 K) as an enhancement, of the large particles on the tail of the sulfuric acid droplet size distribution. The major increases in number and volume indicative of the main body of the NAT cloud are not seen in these Arctic investigations until 191 to 192 K, which corresponds to an apparent saturation ratio of HNO3 with respect to NAT of about 10, unlike the Antarctic where clouds were encountered at saturation ratios near 1. A decrease in the number of particles was observed in regions in which the airmass was denitrified, i.e. NOy, the sum of all reactive nitrogen species, was reduced. This was especially true for the larger particles on the upper tail of the sulfate size distribution. The loss of these largest particles supports the idea that denitrification may be the result of the preferential nucleation and growth of NAT on only the largest sulfate particles, which then sediment out of the airmass.

An improved forward scattering spectrometer probe, the FSSP‐300, was developed for the Airborne Arctic Stratospheric Expedition. The 300 measures particles in the size range 0.3 μm to 20 μm and has a greater sensitivity and faster time response than its predecessor, the FSSP‐100X. An intensive characterization of this probe's operating characteristics has been made and its limitations evaluated. Measurements from this probe are affected by Mie scattering ambiguities and index of refraction uncertainties, nonuniform laser intensity, uncertainties in sample volume definition, and time response roll‐off. Correction algorithms have been developed to account for some of the probe limitations. After applying these corrections, the uncertainties in number and mass concentration are on the order of 25% and 60%, respectively.

Instrumented aircraft and radar were used to investigate the microphysical, electrical, and dynamic evolution of the life cycle of a small thunderstorm which occurred in southeastern Montana. The observations commenced as precipitation development was just beginning, continued through the active stage of growth as the cloud produced graupel up to 8 to 9 mm diameter and reflectivities aloft of 45 dBZ, through the dissipation stage when only an anvil with a trail of light precipitation remained. The largest particles and the primary development of precipitation were found to occur in the fringes of the updraft. The electric fields inside the cloud did not exceed 100 V m−1 until 5 mm graupel, ice particle concentrations of 10 L−1, and reflectivities of 35 dBZ were already present, but then rapidly electrified to produce a single intracloud discharge 8 min later, near the peak of microphysical development. Early in the electrical development of the cloud when observed electric fields were only 200 V m−1, negative charge accumulation was observed near the 7 km (−20°C) level and was associated with the high reflectivity region. In the early stages of precipitation fallout, particle charge measurements near 4.5 km showed primarily negatively charged particles which appeared to be associated with precipitation falling from the cloud. Less than 5 to 10% of the observed particles larger than 100 μm were carrying charges larger than 5 pC, the detection limit of the instrument. These observations are discussed from the point of view of charge generation in thunderstorms, particularly, charge transfer between colliding ice particles.

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The role of noninductive graupel-ice charge separation in the early electrification of the July 31, 1984, New Mexico mountain thunderstorm is assessed with a three-dimensional kinematic cloud model along with multiple Doppler radar and in situ measurements. Observations of the early electrification rate and the electric field distribution are consistent with modeled values that result when the noninductive mechanism works under the influence of convective motions and precipitation growth. An increase in ice particle concentrations and sizes, arising from vigorous precipitation growth, accelerates graupel-ice collision rates and hence the noninductive charging rate. Growing graupel particles experience increasing fall speed as they rise toward the top of the updraft. The resulting vertical flux convergence of graupel containing charge from previous noninductive collisions is a significant factor in the growth of the main negative charge density. This implies that a combination of air motion, precipitation interaction, and sedimentation contributes to the rapid intensification of storm electric fields. The linear electrification phase, which begins with the cessation of convective growth, is caused by a roughly constant noninductive charging rate and by the separation of negatively charged graupel and positively charged smaller ice particles by differential sedimentation, downdrafts, and horizontal advection in vertically sheared flow. When the sign reversal temperature for noninductive charging is assumed to be -10øC, the model results are characterized by a main negative charge in middle levels and provide the best overall agreement with the in situ field measurements in the July 31 storm. For a sign reversal temperature of -21øC the model results are characterized by a main positive charge center in middle levels, and the electric field polarity is opposite to the polarity measured at low and middle levels of the storm. The model and observational data, combined with findings of some laboratory studies, support the hypothesis that the actual reversal temperature in the July 31 storm is around -10øC. When the model includes the inductive graupel-droplet charging mechanism in addition to the noninductive mechanism, the effect of inductive charging is secondary to that of noninductive charging. The net effect of adding induction is dissipative. For example, the maximum field strength at the location of the aircraft measurements is slightly less than in the case where the noninductiVe mechanism acts alone. Weak charge screening layers were found to develop on the boundary of the modeled cloud.