Instrumented Aircraft Research Articles

Comparative analysis of evapotranspiration (ET), crop water stress index (CWSI), and normalized difference vegetation index (NDVI) to delineate site-specific irrigation management zones in almond orchards

Management zones are an important aspect of precision agriculture as they help to define spatiotemporal areas that share homogenous attributes for site-specific management such as irrigation. In this study, we evaluated the potential of delineating irrigation management zones in almond (Prunus dulcis) orchards using three different variables: evapotranspiration (ET), crop water stress index (CWSI), and normalized difference vegetation index (NDVI). Multispectral and thermal images were collected on 11 days in June and July of 2020 using an instrumented aircraft flown over an almond orchard in the Central Valley of California. Obtained images were used to compute ET, CWSI, and NDVI. An unsupervised k-means clustering algorithm was used to delineate the field into management zones, and silhouette width was used to determine the optimum number of zones. Regardless of the input variable and collection date, the optimum number of irrigation management zones was identified as two. ET- and CWSI-based management zones addressed higher spatial variability in the field (up to 73.6 %) than NDVI (up to 68 %). Similarly, the level of agreement between management zones delineated using ET and CWSI was strong (kappa coefficient: 0.84 to 1.00). ET- and CWSI-based management zones also showed a trend (p < 0.1) in distinguishing the difference in the irrigation application and almond yield between the two delineated zones. This study shows that CWSI can be as effective as ET in delineating irrigation management zones, and both inputs sensitive to capture the vegetation responses to irrigation management during the summer growing season. Results from this study can be useful for growers and decision makers to practice precision irrigation management in woody perennial cropping systems.

CAIPEEX: Indian Cloud Seeding Scientific Experiment

Abstract The demand for effective methods to augment precipitation over arid regions of India has been increasing over the past several decades as the changing climate brings warmer average temperatures. In the fourth phase of the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX IV), a scientific investigation was conducted over a rain-shadow region of the Western Ghats mountains in India. The primary objective was to investigate the efficacy of hygroscopic seeding in convective clouds and to develop a cloud seeding protocol. CAIPEEX IV followed the World Meteorological Organization (WMO) recommendations in a peer-reviewed report with physical, statistical, and numerical investigations. The initial results of the campaign in the monsoon period of 2018 and 2019 with two instrumented aircraft, a ground-based dual-polarization C-band radar, a network of rain gauges, radiosondes, and surface aerosol measurements are reported here. The hygroscopic seeding material was detected in cloud droplets and key cloud microphysical processes in the seeding hypothesis were tracked. The formidable challenges of assessing seeding impacts in convective clouds and the results from 150 seed and 122 no-seed samples of randomized experiments are illustrated. Over 5,000 cloud passes from the airborne campaign provided details about the convective cloud properties as the key indicators for a seeding strategy and the evaluation protocol. The experimental results suggest that cloud seeding can be approached scientifically to reduce uncertainty. The results from this study should interest the scientific community and policymakers concerned with climate change’s impact on precipitation and how to mitigate rainfall deficiencies.

The CLoud–Aerosol–Radiation Interaction and Forcing: Year 2017 (CLARIFY-2017) measurement campaign

Abstract. The representations of clouds, aerosols, and cloud–aerosol–radiation impacts remain some of the largest uncertainties in climate change, limiting our ability to accurately reconstruct past climate and predict future climate. The south-east Atlantic is a region where high atmospheric aerosol loadings and semi-permanent stratocumulus clouds are co-located, providing an optimum region for studying the full range of aerosol–radiation and aerosol–cloud interactions and their perturbations of the Earth's radiation budget. While satellite measurements have provided some useful insights into aerosol–radiation and aerosol–cloud interactions over the region, these observations do not have the spatial and temporal resolution, nor the required level of precision to allow for a process-level assessment. Detailed measurements from high spatial and temporal resolution airborne atmospheric measurements in the region are very sparse, limiting their use in assessing the performance of aerosol modelling in numerical weather prediction and climate models. CLARIFY-2017 was a major consortium programme consisting of five principal UK universities with project partners from the UK Met Office and European- and USA-based universities and research centres involved in the complementary ORACLES, LASIC, and AEROCLO-sA projects. The aims of CLARIFY-2017 were fourfold: (1) to improve the representation and reduce uncertainty in model estimates of the direct, semi-direct, and indirect radiative effect of absorbing biomass burning aerosols; (2) to improve our knowledge and representation of the processes determining stratocumulus cloud microphysical and radiative properties and their transition to cumulus regimes; (3) to challenge, validate, and improve satellite retrievals of cloud and aerosol properties and their radiative impacts; (4) to improve the impacts of aerosols in weather and climate numerical models. This paper describes the modelling and measurement strategies central to the CLARIFY-2017 deployment of the FAAM BAe146 instrumented aircraft campaign, summarizes the flight objectives and flight patterns, and highlights some key results from our initial analyses.

Aerosol data assimilation in the MOCAGE chemical transport model during the TRAQA/ChArMEx campaign: lidar observations

Abstract. This paper presents the first results about the assimilation of CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) extinction coefficient measurements onboard the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite in the MOCAGE (MOdèle de Chimie Atmosphérique à Grande Echelle) chemistry transport model of Météo-France. This assimilation module is an extension of the aerosol optical depth (AOD) assimilation system already presented by Sič et al. (2016). We focus on the period of the TRAQA (TRAnsport à longue distance et Qualité de l’Air dans le bassin méditerranéen) field campaign that took place during summer 2012. This period offers the opportunity to have access to a large set of aerosol observations from instrumented aircraft, balloons, satellite and ground-based stations. We evaluate the added value of CALIOP assimilation with respect to the model free run by comparing both fields to independent observations issued from the TRAQA field campaign. In this study we focus on the desert dust outbreak which happened during late June 2012 over the Mediterranean Basin (MB) during the TRAQA campaign. The comparison with the AERONET (Aerosol Robotic Network) AOD measurements shows that the assimilation of CALIOP lidar observations improves the statistics compared to the model free run. The correlation between AERONET and the model (assimilation) is 0.682 (0.753); the bias and the root mean square error (RMSE), due to CALIOP assimilation, are reduced from −0.063 to 0.048 and from 0.183 to 0.148, respectively. Compared to MODIS (Moderate-resolution Imaging Spectroradiometer) AOD observations, the model free run shows an underestimation of the AOD values, whereas the CALIOP assimilation corrects this underestimation and shows a quantitative good improvement in terms of AOD maps over the MB. The correlation between MODIS and the model (assimilation) during the dust outbreak is 0.47 (0.52), whereas the bias is −0.18 (−0.02) and the RMSE is 0.36 (0.30). The comparison of in situ aircraft and balloon measurements to both modelled and assimilated outputs shows that the CALIOP lidar assimilation highly improves the model aerosol field. The evaluation with the LOAC (Light Optical Particle Counter) measurements indicates that the aerosol vertical profiles are well simulated by the direct model but with a general underestimation of the aerosol number concentration, especially in the altitude range 2–5 km. The CALIOP assimilation improves these results by a factor of 2.5 to 5. Analysis of the vertical distribution of the desert aerosol concentration shows that the aerosol dust transport event is well captured by the model but with an underestimated intensity. The assimilation of CALIOP observations allows the improvement of the geographical representation of the event within the model as well as its intensity by a factor of 2 in the altitude range 1–5 km.

The structure of turbulence and mixed-phase cloud microphysics in a highly supercooled altocumulus cloud

Abstract. Observations of vertically resolved turbulence and cloud microphysics in a mixed-phase altocumulus cloud are presented using in situ measurements from an instrumented aircraft. The turbulence spectrum is observed to have an increasingly negative skewness with distance below cloud top, suggesting that long-wave radiative cooling from the liquid cloud layer is an important source of turbulence kinetic energy. Turbulence measurements are presented from both the liquid cloud layer and ice virga below. Vertical profiles of both bulk and microphysical liquid and ice cloud properties indicate that ice is produced within the liquid layer cloud at a temperature of −30 ∘C. These high-resolution in situ measurements support previous remotely sensed observations from both ground-based and space-borne instruments and could be used to evaluate numerical model simulations of altocumulus clouds at spatial scales from eddy-resolving models to global numerical weather prediction models and climate simulations.

Investigation of factors controlling PM2.5 variability across the South Korean Peninsula during KORUS-AQ.

The Korea – United States Air Quality Study (May – June 2016) deployed instrumented aircraft and ground-based measurements to elucidate causes of poor air quality related to high ozone and aerosol concentrations in South Korea. This work synthesizes data pertaining to aerosols (specifically, particulate matter with aerodynamic diameters <2.5 micrometers, PM2.5) and conditions leading to violations of South Korean air quality standards (24-hr mean PM2.5 < 35 μg m−3). PM2.5 variability from AirKorea monitors across South Korea is evaluated. Detailed data from the Seoul vicinity are used to interpret factors that contribute to elevated PM2.5. The interplay between meteorology and surface aerosols, contrasting synoptic-scale behavior vs. local influences, is presented. Transboundary transport from upwind sources, vertical mixing and containment of aerosols, and local production of secondary aerosols are discussed. Two meteorological periods are probed for drivers of elevated PM2.5. Clear, dry conditions, with limited transport (Stagnant period), promoted photochemical production of secondary organic aerosol from locally emitted precursors. Cloudy humid conditions fostered rapid heterogeneous secondary inorganic aerosol production from local and transported emissions (Transport/Haze period), likely driven by a positive feedback mechanism where water uptake by aerosols increased gas-to-particle partitioning that increased water uptake. Further, clouds reduced solar insolation, suppressing mixing, exacerbating PM2.5 accumulation in a shallow boundary layer. The combination of factors contributing to enhanced PM2.5 is challenging to model, complicating quantification of contributions to PM2.5 from local versus upwind precursors and production. We recommend co-locating additional continuous measurements at a few AirKorea sites across South Korea to help resolve this and other outstanding questions: carbon monoxide/carbon dioxide (transboundary transport tracer), boundary layer height (surface PM2.5 mixing depth), and aerosol composition with aerosol liquid water (meteorologically-dependent secondary production). These data would aid future research to refine emissions targets to further improve South Korean PM2.5 air quality.

Relationship between airborne electrical and total water content measurements in ice clouds

Abstract During the High Altitude Ice Crystal -High Ice Water Content (HAIC-HIWC) project, instrumented aircraft were flown in the vicinity and inside deep tropical convective clouds. Among the probes installed on one of these aircraft, were the Isokinetic Probe (IKP2), to retrieve the cloud total water content (TWC) and the AMPERA (Atmospheric Measurement of Potential and Electric field on Aircraft) system to provide information on the electrostatic state of the atmosphere and the aircraft. AMPERA is an electric field mill network which locally measures the electrostatic field at the aircraft fuselage. The distribution and amplitude of the electrostatic field on the aircraft skin depends on the atmospheric electrostatic field around the aircraft and the net electric charge of the aircraft. This latter parameter depends on the balance between the triboelectric current due to the impact of the cloud particles on the aircraft fuselage, the current due to the charged particles emitted by the engines, and the corona current emitted by the aircraft. Based on the flights of the HAIC-HIWC campaigns, which were conducted almost exclusively in cloud composed of ice particles, a comparison between the total water content recorded by microphysical sensor and the aircraft net charge has highlighted the possibility of deducing an estimate of the TWC from the aircraft electrical potential. In contrast to conventional TWC probes which sample a local area of the atmosphere, the AMPERA system uses the aircraft as a sensor and provides an overall estimation of its net TWC exposure. This study provides the first results of the efficacy of the electrostatic method through comparisons with direct in-situ bulk TWC measurements in ice clouds.

Numerical and experimental study of aircraft structural health

The purpose of this work is to monitor the structural health of the Portuguese Air Force (PoAF) EPSILON TB30 fleet by measuring the dynamic behaviour of aircraft’s critical components towards the optimization of maintenance programme scheduling. The mission load spectrum and the structural response are simultaneously measured using a combination of accelerometers and strain-gauges, enabling the calculation of individual transference functions for each critical component monitored. The EPSILON TB30 fleet was divided into two different types of aircrafts: a) IMA-Highly Instrumented Aircrafts which are able to capture vertical accelerations and strain at critical locations and b) LIA-Less Instrumented Aircrafts that make use of the transference functions for mapping the captured acceleration data to stress at pre-selected structural hotspots. The fleet operation is continuously analysed to calculate the fatigue damage of each component and predict the operation limit for each aircraft. In this context, finite element models of critical components are used to define the critical locations of sensors used for monitoring stress in those locations. The maximum principal stress zones of the 2nd bulkhead beam was obtained and are consistent with the manufacturer’s reports that place fatigue crack initiation near the bottom filleted joint of the innermost rib, during real scale fatigue test. Mission is analysed using the structural health monitoring platform PRODDIA™ Aero which uses time and frequency-based fatigue models to predict the structural health of the entire fleet.

Inner Structures of Snow Clouds over the Sea of Japan Observed by Instrumented Aircraft: A Review

Inner Structures of Snow Clouds over the Sea of Japan Observed by Instrumented Aircraft: A Review

Aerial Interyear Comparison and Quantification of Methane Emissions Persistence in the Bakken Formation of North Dakota, USA.

We performed an infrared optical gas imaging (OGI) survey by helicopter of hydrocarbon emissions in the Bakken formation of North Dakota. One year after an earlier survey of 682 well pads in September of 2014, the same helicopter crew resurveyed 353 well pads in 2015 to examine the persistence of emissions. Twenty-one newly producing well pads were added in the same sampling blocks. An instrumented aircraft was also used to quantify emissions from 33 plumes identified by aerial OGI. Well pads emitting methane and ethane in 2014 were far more likely to be emitting in 2015 than would be expected by chance; Monte Carlo simulations suggest >5σ deviation ( p < 0.0001) from random assignment of detectable emissions between survey years. Scaled up using basin-wide leakage estimates, the emissions quantified by aircraft are sufficient to explain previously observed basin-wide emissions of methane and ethane.

Atmospheric turbulence effects on sonic boom signatures

Two measurement campaigns were conducted as part of a study to quantify the effect of atmospheric turbulence on sonic boom propagation. Supersonic overflights were conducted at the NASA Armstrong Flight Research Center and the Kennedy Space Center to provide different atmospheric conditions for study. Measurements were made of the strength of the turbulence along with the height of the atmospheric boundary layer. Multiple microphone arrays recorded the sonic booms from instrumented aircraft. This work will present statistics detailing the variation of measured booms as a function of the strength of the turbulence and the propagation distance through the atmospheric boundary layer. [Work supported by NASA.]

Evidence for secondary ice production in Southern Ocean open cellular convection

Ice particles present at temperatures warmer than −9 °C were encountered in unexpectedly high number concentrations (up to 54 L−1) by an instrumented aircraft over the Southern Ocean (SO), off the southwest coast of Tasmania, Australia, on 7 September 2013. The sampled clouds were precipitating, characterized by mixed‐phase, open‐cellular shallow convection. These clouds were present within a large‐scale environment characterized by cold air advection, in a pristine air mass for over 72 h. Using a Cloud and Aerosol Spectrometer, aerosol particles (diameters &gt; 0.6 µm) size and number concentrations were measured and ice nucleating particle (INP) number concentrations were estimated with a recognized ice nuclei parametrization scheme. The estimated INP number concentrations were in the range of 10−5–10−1 L−1 at temperature above −9 °C, which is up to three orders of magnitude less than the ice number concentrations typically observed. The high ice number concentrations are largely consistent with the theoretical values when ice crystals are produced via a splinter production. The evidence suggests that secondary ice processes (likely the Hallett–Mossop mechanism) were playing a key role in generating the high ice number concentrations observed. Satellite observations from an A‐Train overpass in the neighbourhood during the flight period reveal a qualitatively consistent story, with patchy, mixed‐phase (but predominantly supercooled liquid water) clouds observed at cloud‐top temperatures around −6 °C. Using back trajectory calculations, these clouds are tracked over 23 and 46 h with A‐Train observations. The presence of these clouds is found to be common over the SO during this period of time. This suggests that the ice particles present in a relatively warm temperature range could potentially be commonplace, within the widespread (up to thousands of kilometres) shallow convective cloud fields over the SO. These clouds may have important implication for the energy budget and precipitation production over this climatically important region.

Large‐scale enhancement in aerosol absorption in the lower free troposphere over continental India during spring

AbstractAerosol absorption in the lower troposphere over continental India was assessed using extensive measurements of the vertical distribution of absorption coefficients aboard an instrumented aircraft. Measurements were made from seven base stations during winter (November–December 2012) and spring (April–May 2013), supplemented by the data from the networks of surface observatories. A definite enhancement in aerosol absorption has been observed in the lower free troposphere over the Indo‐Gangetic Plain (IGP) during spring, along with a reduction near the surface. The regional mean aerosol absorption optical depth (AAOD) over IGP, which was derived from aircraft observations (integrated from the ground to 3 km), increased from 0.020 ± 0.009 in winter to 0.048 ± 0.01 in spring. The columnar AAOD depicted weak and distinctly different seasonal variations than that of surface level black carbon mass concentrations. This contrasting difference in the seasonality indicates the presence of elevated layers of absorbing aerosols during spring in association with the long‐range transport and vertical convective lofting of aerosols.

Observations of monsoon convective cloud microphysics over India and role of entrainment‐mixing

AbstractMicrophysical characteristics of premonsoon and monsoon deep cumuli over India observed by an instrumented aircraft are contrasted focusing on influences of environmental conditions and entrainment‐mixing processes. Differences in the lower tropospheric temperature and moisture profiles lead to contrasting undiluted cloud buoyancy profiles around the cloud base, larger in the premonsoon case. It is argued that this affects the variation of the mean and maximum cloud droplet number concentrations and the droplet radius within the lowest several hundred meters above the cloud base. The conserved‐variable thermodynamic diagram analysis suggests that entrained parcels originate from levels close to the observational level. Mixing processes and their impact on the droplet size distribution (DSD) are investigated contrasting 1 Hz and 10 Hz observations. Inhomogeneous‐type mixing, likely because of unresolved small‐scale structures associated with active turbulent stirring, is noted at cloud edge volumes where dilution is significant and DSDs shift toward smaller sizes with reduced droplet number concentrations due to complete evaporation of smaller droplets and partial evaporation of larger droplets. DSDs within cloud core volumes suggest that the largest droplets are formed in the least diluted volumes where raindrops can form at higher levels; no superadiabatic droplet growth is observed. The typical diluted parcel size is approximately 100–200 m for cloud edge volumes, and it is much smaller, 10–20 m, for cloud core volumes. Time scale analysis indicates the possibility of inhomogeneous type mixing within the diluted cloud edge volumes at spatial scales of a 100 m or more.

Airborne quantification of upper tropospheric NOx production from lightning in deep convective storms over the United States Great Plains

AbstractThe reported range for global production of nitrogen oxides (NOx = NO + NO2) by lightning remains large (e.g., 32 to 664 mol NOx flash−1), despite incorporating results from over 30 individual laboratory, theoretical, and field studies since the 1970s. Airborne and ground‐based observations from the Deep Convective Clouds and Chemistry experiment in May and June 2012 provide a new data set for calculating moles of NOx produced per lightning flash, P(NOx), in thunderstorms over the United States Great Plains. This analysis utilizes a combination of in situ observations of storm inflow and outflow from three instrumented aircraft, three‐dimensional spatial information from ground‐based radars and satellite observations, and spatial and temporal information for intracloud and cloud‐to‐ground lightning flashes from ground‐based lightning mapping arrays. Evaluation of two analysis methods (e.g., a volume‐based approach and a flux‐based approach) for converting enhancements in lightning‐produced NOx from volume‐based mixing ratios to moles NOx flash−1 suggests that both methods equally approximate P(NOx) for storms with elongated anvils, while the volume‐based approach better approximates P(NOx) for storms with circular‐shaped anvils. Results from the more robust volume‐based approach for three storms sampled over Oklahoma and Colorado during DC3 suggest a range of 142 to 291 (average of 194) moles NOx flash−1 (or 117–332 mol NOx flash−1 including uncertainties). Although not vastly different from the previously reported range for storms occurring in the Great Plains (e.g., 21–465 mol NOx flash−1), results from this analysis of DC3 storms offer more constrained upper and lower limits for P(NOx) in this geographical region.

Characterization of Hydrometeors in Sahelian Convective Systems with an X-Band Radar and Comparison with In Situ Measurements. Part II: A Simple Brightband Method to Infer the Density of Icy Hydrometeors

AbstractA simple scheme that is based on the shape and intensity of the radar bright band is used to infer the density of hydrometeors just above the freezing level in Sahelian mesoscale convective systems (MCS). Four MCS jointly observed by a ground-based X-band radar and by an instrumented aircraft as part of the Megha-Tropiques algorithm-validation campaign during August 2010 in Niamey, Niger, are analyzed. The instrumented aircraft (with a 94-GHz radar and various optical probes on board) provided mass–diameter laws for the particles sampled during the flights. The mass–diameter laws derived from the ground-radar vertical profile of reflectivity (VPR) for each flight are compared with those derived from the airborne measurements. The density laws derived by both methods are consistent and encourage further use of the simple VPR scheme to quantify hydrometeor density laws and their variability for various analyses (microphysical processes and icy-hydrometeor scattering and radiative properties).

Characterization of Hydrometeors in Sahelian Convective Systems with an X-Band Radar and Comparison with In Situ Measurements. Part I: Sensitivity of Polarimetric Radar Particle Identification Retrieval and Case Study Evaluation

AbstractThe particle identification scheme developed by Dolan and Rutledge for X-band polarimetric radar is tested for the first time in Africa and compared with in situ measurements. The data were acquired during the Megha-Tropiques mission algorithm-validation campaign that occurred in Niger in 2010. The radar classification is compared with the in situ observations gathered by an instrumented aircraft for the 13 August 2010 squall-line case. An original approach has been developed for the radar–in situ comparison: it consists of simulating synthetic radar variables from the microphysical-probe information and comparing the two datasets in a common “radar space.” The consistency between the two types of observation is good considering the differences in sampling illustrated in the paper. The time evolution of the hydrometeor types and their relative proportion in the convective and stratiform regions are analyzed. The farther away from the convection one looks, the more aggregation dominates, riming diminishes, and hydrometeors are less dense. Particle identification based on the polarimetric radar will be applied to a 5-yr African dataset in the future.

Observational and simulated cloud microphysical features of rain formation in the mixed phase clouds observed during CAIPEEX

Cloud microphysical observations of rain formation in mixed phase monsoon clouds (from 10 to −9°C) using instrumented aircraft during Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) are presented. The drop size and particle size distributions are broader in the mixed phase region, indicating efficient growth of liquid as well as ice phase. Aircraft observations noticed higher ice particle concentrations in Hallet–Mossop zone (−3 to −8°C) with existence of smaller and larger cloud droplets, rimed needles columns, and graupel particles. Observations strongly suggested the active presence of Hallet–Mossop (1974) process in this cloud. The higher correlations found between slope and intercept parameters of exponential size distributions can be attributed to the efficient secondary ice production as well as to the aggregation growth of ice particles. Large Eddy Simulation (LES) of these clouds are compared with observed cloud microphysical properties, also illustrated the important role of Hallet–Mossop (HM) process and its link with warm rain and graupel formation. The raindrop freezing plays a crucial role in graupel formation in early stage of ice development. The observed mean values of microphysical parameters including liquid water content, ice water content, ice number concentrations, and reflectivity showed good agreement with model simulations. Primary ice nuclei have only a minor role in the total ice mass in these clouds.

Seasonal variation of vertical distribution of aerosol single scattering albedo over Indian sub-continent: RAWEX aircraft observations

To characterize the vertical distribution of aerosols and its seasonality (especially the single scattering albedo, SSA) extensive profiling of aerosol scattering and absorption coefficients have been carried out using an instrumented aircraft from seven base stations spread across the Indian mainland during winter 2012 and spring/pre-monsoon 2013 under the Regional Aerosol Warming Experiment (RAWEX). Spatial variation of the vertical profiles of the asymmetry parameter, the wavelength exponent of the absorption coefficient and the single scattering albedo, derived from the measurements, are used to infer the source characteristics of winter and pre-monsoon aerosols as well as the seasonality of free tropospheric aerosols. The relatively high value of the wavelength exponent of absorption coefficient over most of the regions indicates the contribution from biomass burning and dust aerosols up to lower free tropospheric altitudes. A clear enhancement in aerosol loading and its absorbing nature is seen at lower free troposphere levels (above the planetary boundary layer) over the entire mainland during spring/pre-monsoon season compared to winter, whereas concentration of aerosols within the boundary layer showed a decrease from winter to spring. This could have significant implications on the aerosol heating structure over the Indian region and hence the regional climate.

A Dryline in Southeast Wyoming. Part II: Airborne In Situ and Raman Lidar Observations

Abstract Part I of this study describes the mesoscale structure of a dryline over southeastern Wyoming. This dryline formed just east of the western rim of the high plains on 22 June 2010 and became more defined as it progressed eastward during the afternoon. Part I also describes the numerically simulated structure and evolution of this dryline and the observed initiation of deep convection in the vicinity of the dryline. An instrumented aircraft, the University of Wyoming King Air, repeatedly flew across this dryline, mostly low enough to penetrate the moist-air wedge east of the dryline. Flight-level in situ data along these low-level penetrations indicate relatively high values of convective available potential energy (CAPE; &amp;gt;1500 J kg−1), yet low convective inhibition, within a few kilometers of the dryline. Water vapor transects obtained from a compact nadir-pointing Raman lidar aboard the aircraft reveal an extremely sharp humidity gradient below flight level along the dryline, coinciding with the fineline seen in operational weather radar base reflectivity imagery. They also reveal several plumes of higher specific humidity within the dry elevated mixed layer above the moist-air wedge, possibly precursors of cumulus clouds. The vertical structure of the dryline revealed by Raman lidar and the flight-level data correspond well to that in the high-resolution numerical simulation.