Shallow, maritime cumuli are ubiquitous over much of the tropical oceans, and characterizing their properties is important to understanding weather and climate. The Rain in Cumulus over the Ocean (RICO) field campaign, which took place during November 2004–January 2005 in the trades over the western Atlantic, emphasized measurements of processes related to the formation of rain in shallow cumuli, and how rain subsequently modifies the structure and ensemble statistics of trade wind clouds. Eight weeks of nearly continuous S-band polarimetric radar sampling, 57 flights from three heavily instrumented research aircraft, and a suite of ground- and ship-based instrumentation provided data on trade wind clouds with unprecedented resolution. Observational strategies employed during RICO capitalized on the advances in remote sensing and other instrumentation to provide insight into processes that span a range of scales and that lie at the heart of questions relating to the cause and effects of rain from shallow maritime cumuli.

The vertical evolution of microphysics in trade-wind cumuli (Cu) observed from the NCAR C-130 research aircraft during one flight of the RICO (Rain in Cumulus Over the Ocean) study is analyzed. Conditional sampling of > 200 Cu traversed on this flight is used to chose Cu for which the aircraft penetrated single and growing Cu turrets about 250-m below cloud top where maximum LWC is often found and where radar has often observed initial stages of precipitation. The vertical evolution of the sampled set of Cu was assumed to follow Lagrangian behavior. The entrainment rate, entrained parcel scales, mixing mechanisms, and effects on the droplet size distribution are measured and evaluated. A parcel model is applied over the 1100-m maximum Cu height of the traverses to determine the relationship between the observed large number of small droplets and the fewer ultra-giant sea-salt nuclei (UGN) in order to assess the role of these nuclei in evolving the size spectrum and in causing a growing "drizzle tail". New insight on these topics is obtained by using the PVM (Particle Volume Monitor) probe to measure incloud microphysics with 10-cm resolution.The results include the following: Entrainment causes primarily dilution of the drops without significant size changes, thus either extreme inhomogeneous mixing or more likely homogeneous mixing resulting from mixing with cool and humid entrained air take place. The entrained parcels are surprisingly small following lognormal behavior and decaying rapidly upon entering the Cu, as a result super-adiabatic drops are not evident. The entrained parcels are consistent with the Bragg-scattering "mantle echo" often observed by radar in small Cu. The FSSP (Forward Scattering Spectrometer Probe) droplet spectra are nearly constant with height. These "self-preserving" spectra are a result of an approximate balance between dilution by entrainment of droplets originating at cloud base, droplet activation on entrained CCN (cloud condensation nuclei), and detrainment and coalescence losses. Sea-salt nuclei follow Woodcock's wind dependence, and are shown with the parcel model to play an important role in forming the observed drizzle that increases with cloud height. Accretion is the dominant coalescence mechanism near cloud top in these Cu.

Weather and climate models are challenged by uncertainties and biases in simulating Southern Ocean (SO) radiative fluxes that trace to a poor understanding of cloud, aerosol, precipitation and radiative processes, and their interactions. Projects between 2016 and 2018 used in-situ probes, radar, lidar and other instruments to make comprehensive measurements of thermodynamics, surface radiation, cloud, precipitation, aerosol, cloud condensation nuclei (CCN) and ice nucleating particles over the SO cold waters, and in ubiquitous liquid and mixed-phase cloudsnucleating particles over the SO cold waters, and in ubiquitous liquid and mixed-phase clouds common to this pristine environment. Data including soundings were collected from the NSF/NCAR G-V aircraft flying north-south gradients south of Tasmania, at Macquarie Island, and on the RV Investigator and RSV Aurora Australis. Synergistically these data characterize boundary layer and free troposphere environmental properties, and represent the most comprehensive data of this type available south of the oceanic polar front, in the cold sector of SO cyclones, and across seasons.Results show a largely pristine environments with numerous small and few large aerosols above cloud, suggesting new particle formation and limited long-range transport from continents, high variability in CCN and cloud droplet concentrations, and ubiquitous supercooled water in thin, multi-layered clouds, often with small-scale generating cells near cloud top. These observations demonstrate how cloud properties depend on aerosols while highlighting the importance of confirmed low clouds were responsible for radiation biases. The combination of models and observations is examining how aerosols and meteorology couple to control SO water and energy budgets.

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Using the National Science Foundation (NSF)-NCAR Gulfstream V and the NSF-Wyoming King Air research aircraft during the Terrain-Induced Rotor Experiment (T-REX) in March-April 2006, six cases of Sierra Nevada mountain waves were surveyed with 126 cross-mountain legs. The goal was to identify the influence of the tropopause on waves entering the stratosphere. During each flight leg, part of the variation in observed parameters was due to parameter layering, heaving up and down in the waves. Diagnosis of the combined wave-layering signal was aided with innovative use of new GPS altitude measurements. The ozone and water vapor layering correlated with layered Bernoulli function and cross-flow speed.GPS-corrected static pressure was used to compute the vertical energy flux, confirming, for the first time, the Eliassen-Palm relation between momentum and energy flux (EF ϭ ϪU • MF). Kinetic (KE) and potential (PE) wave energy densities were also computed. The equipartition ratio (EQR ϭ PE/KE) changed abruptly across the tropopause, indicating partial wave reflection. In one case (16 April 2006) systematically reversed momentum and energy fluxes were found in the stratosphere above 12 km. On a "wave property diagram," three families of waves were identified: up-and downgoing long waves (30 km) and shorter (14 km) trapped waves. For the latter two types, an explanation is proposed related to secondary generation near the tropopause and reflection or secondary generation in the lower stratosphere.

During the Deep Propagating Gravity Wave Experiment (DEEPWAVE) project in June and July 2014, the Gulfstream V research aircraft flew 97 legs over the Southern Alps of New Zealand and 150 legs over the Tasman Sea and Southern Ocean, mostly in the low stratosphere at 12.1-km altitude. Improved instrument calibration, redundant sensors, longer flight legs, energy flux estimation, and scale analysis revealed several new gravity wave properties. Over the sea, flight-level wave fluxes mostly fell below the detection threshold. Over terrain, disturbances had characteristic mountain wave attributes of positive vertical energy flux (EF z ), negative zonal momentum flux, and upwind horizontal energy flux. In some cases, the fluxes changed rapidly within an 8-h flight, even though environmental conditions were nearly unchanged. The largest observed zonal momentum and vertical energy fluxes were MF x 5 2550 mPa and EF z 5 22 W m 22 , respectively. A wide variety of disturbance scales were found at flight level over New Zealand. The vertical wind variance at flight level was dominated by short ''fluxless'' waves with wavelengths in the 6-15-km range. Even shorter scales, down to 500 m, were found in wave breaking regions. The wavelength of the flux-carrying mountain waves was much longer-mostly between 60 and 150 km. In the strong cases, however, with EF z . 4 W m 22, the dominant flux wavelength decreased (i.e., ''downshifted'') to an intermediate wavelength between 20 and 60 km. A potential explanation for the rapid flux changes and the scale ''downshifting'' is that low-level flow can shift between ''terrain following'' and ''envelope following'' associated with trapped air in steep New Zealand valleys.

The Convective Transport of Active Species in the Tropics (CONTRAST) experiment was conducted from Guam (13.5° N, 144.8° E) during January-February 2014. Using the NSF/NCAR Gulfstream V research aircraft, the experiment investigated the photochemical environment over the tropical western Pacific (TWP) warm pool, a region of massive deep convection and the major pathway for air to enter the stratosphere during Northern Hemisphere (NH) winter. The new observations provide a wealth of information for quantifying the influence of convection on the vertical distributions of active species. The airborne in situ measurements up to 15 km altitude fill a significant gap by characterizing the abundance and altitude variation of a wide suite of trace gases. These measurements, together with observations of dynamical and microphysical parameters, provide significant new data for constraining and evaluating global chemistry climate models. Measurements include precursor and product gas species of reactive halogen compounds that impact ozone in the upper troposphere/lower stratosphere. High accuracy, in-situ measurements of ozone obtained during CONTRAST quantify ozone concentration profiles in the UT, where previous observations from balloon-borne ozonesondes were often near or below the limit of detection. CONTRAST was one of the three coordinated experiments to observe the TWP during January-February 2014. Together, CONTRAST, ATTREX and CAST, using complementary capabilities of the three aircraft platforms as well as ground-based instrumentation, provide a comprehensive quantification of the regional distribution and vertical structure of natural and pollutant trace gases in the TWP during NH winter, from the oceanic boundary to the lower stratosphere.

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