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WB-57
WB57
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Harvard Hydroxyl Experiment

OH is detected by direct laser induced fluorescence in the (0-1) band of the 2?-2? electronic transition. A pulsed dye-laser system produces frequency tunable laser light at 282 nm. An on-board frequency reference cell is used by a computer to lock the laser to the appropriate wavelength. Measurement of the signal is then made by tuning the laser on and off resonance with the OH transition.

Stratospheric air is channeled into the instrument using a double-ducted system that both maintains laminar flow through the detection region and slows the flow from free stream velocity (200 m/s) to 40 m/s. The laser light is beam-split and directed to two detection axes where it passes through the stratospheric air in multipass White cells.

Fluorescence from OH (centered at 309 nm) is detected orthogonal to both the flow and the laser propagation using a filtered PMT assembly. Optical stability is checked periodically by exchanging the 309 nm interference filter with a filter centered at 302 nm, where Raman scattering of N2 is observed.

HO2 is measured as OH after chemical titration with nitric oxide: HO2 + NO → OH + NO2. Variation of added NO density and flow velocity as well as the use of two detection axes aid in diagnosis of the kinetics of this titration. Measurements of ozone (by uv absorption) and water vapor (by photofragment fluorescence) are made as diagnostics of potential photochemical interference from the mechanism: O3 + hv (282 nm) → O(1D) + O2, followed by: O(1D) + H2O → OH + OH

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Cloud Spectrometer and Impactor

The Cloud Spectrometer and Impactor (CSI) combines the counterflow virtual impactor with a new lightweight cloud droplet probe to allow for detailed studies of total condensed water (TCW), liquid and ice, in clouds. The CSI can measure TCW from ~ 1 mg/m3 to several g/m3 depending on the configuration; in addition particle sizes from 2 to 50 μm are resolved with the droplet probe. The instrumentation can be mounted externally on most aircraft.

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Counterflow Virtual Impactor

The NCAR counterflow virtual impactor (CVI) (Noone et al., 1988; Twohy et al., 1997) is an airborne instrument that can be used for studies of aerosol/cloud interactions, cloud physics, and climate. At the CVI inlet tip, cloud droplets or ice crystals larger than about 8 µm aerodynamic diameter are separated from the interstitial aerosol and impacted into dry nitrogen gas. This separation is possible via a counterflow stream of nitrogen out the CVI tip, which assures that only larger particles (cloud droplets or ice crystals) are sampled. Because droplets or crystals in a sampling volume of about 200 l/min are impacted into a sample stream of approximately 10 l/min, concentrations within the CVI are significantly enhanced. The water vapor and non-volatile residual nuclei remaining after droplet evaporation are sampled downstream of the inlet with selected instruments. These may include a Lyman-alpha or similar hygrometer, a condensation nucleus counter, an optical particle counter, filters for chemical analyses, or user instruments.

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Cloud Particle Imager

The CPI records high-resolution (2.3 micron pixel size) digital images of particles that pass through the sample volume at speeds up to 200 m/s. CCD camera flashes up to 75 frames per second (fps), potentially imaging more than 25 particles per frame. Camera upgrades capable of bringing frame rate to nearly 500 fps. Real time image processing crops particle images from the full frame, eliminating blank space and compressing data by >1000:1 CPI is designed for ummanned use, with AI parameters to optimize performance without supervision.

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Cloud Integrating Nephelometer

The CIN-100A is designed for aircraft mounting and measures the optical extinction coefficient and asymmetry parameter.

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Cloud Radar System

Clouds are a key element in the global hydrological cycle, and they have a significant role in the Earth’s energy budget through its influence on radiation budgets. Climate model simulations have demonstrated the importance of clouds in moderating and forcing the global energy budget. Despite the crucial role of clouds in climate and the breadth of our current knowledge, there are still many unanswered details. An improved understanding of the radiative impact of clouds on the climate system requires a comprehensive view of clouds that includes their physical dimensions, vertical and horizontal spatial distribution, detailed microphysical properties, and the dynamical processes producing them. However, the lack of fine-scale cloud data is apparent in current climate model simulations.

The Cloud Radar System (CRS) is a fully coherent, polarimeteric Doppler radar that is capable of detecting clouds and precipitation from the surface up to the aircraft altitude in the lower stratosphere. The radar is especially well suited for cirrus cloud studies because of its high sensitivity and fine spatial resolution.

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Cloud Physics Lidar

The Cloud Physics Lidar, or CPL, is a backscatter lidar designed to operate simultaneously at 3 wavelengths: 1064, 532, and 355 nm. The purpose of the CPL is to provide multi-wavelength measurements of cirrus, subvisual cirrus, and aerosols with high temporal and spatial resolution. Figure 1 shows the entire CPL package in flight configuration. The CPL utilizes state-of-the-art technology with a high repetition rate, low pulse energy laser and photon-counting detection. Vertical resolution of the CPL measurements is fixed at 30 m; horizontal resolution can vary but is typically about 200 m. The CPL fundamentally measures range-resolved profiles of volume 180-degree backscatter coefficients. From the fundamental measurement, various data products are derived, including: time-height crosssection images; cloud and aerosol layer boundaries; optical depth for clouds, aerosol layers, and planetary boundary layer (PBL); and extinction profiles. The CPL was designed to fly on the NASA ER-2 aircraft but is adaptable to other platforms. Because the ER-2 typically flies at about 65,000 feet (20 km), onboard instruments are above 94% of the earth’s atmosphere, allowing ER-2 instruments to function as spaceborne instrument simulators. The ER-2 provides a unique platform for atmospheric profiling, particularly for active remote sensing instruments such as lidar, because the spatial coverage attainable by the ER-2 permits studies of aerosol properties across wide regions. Lidar profiling from the ER-2 platform is especially valuable because the cloud height structure, up to the limit of signal attenuation, is unambiguously measured.

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Conical Scanning Submillimeter-wave Imaging Radiometer

The Compact Scanning Submillimeter-wave Imaging Radiometer (CoSSIR) is an airborne, 12-channel, (183 - 874 GHz) total power imaging radiometer that was mainly developed for the measurements of ice clouds. But it can be used for estimation of water vapor profiles and snowfall rates. When first completed and flown in the CRYSTAL-FACE field campaign during July 2002, the system had 15 channels at different frequencies from those listed below. All the receivers and radiometer electronics are housed in a small cylindrical scan head (21.5 cm in diameter and 28 cm in length) that is rotated by a two-axis gimbaled mechanism capable of generating a wide variety of scan profiles. Two calibration targets, one maintained at ambient (cold) temperature and another heated to a hot temperature of about 328 K, are closely coupled to the scan head and rotate with it about the azimuth axis. Radiometric signals from each channel are sampled at 0.01 sec intervals. These signals and housekeeping data are fed to the main computer in an external electronics box.

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Digital Camera System

DCS is a 16-megapixel color infrared digital camera system, providing high resolution imagery for mission tracking purposes Geo-referenced image products may be generated, when used in conjunction with a POS-AV system.

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Tropospheric Ozone and Tracers from Commercial Aircraft Platforms

Ozone is measured in a dual-beam ultraviolet (254 nm) absorption analyzer. Ambient air flows through one absorption cell while air scrubbed of ozone flows through an adjacent one. This allows continuous measurement of both background and absorption signals. Flows are switched between cells by a pair of solenoid valves, which permits monitoring of optical changes. Water vapor is detected with a tunable diode laser spectrometer designed and built by Randy May. This sensor employs a room-temperature near-infrared laser (single mode at about 1.37 microns) and second harmonic detection, rather than direct absorption. Unlike the JPL water instrument, this sensor has an internal absorption path, optimized for the mid-troposphere. Carbon dioxide is measured by its absorption in the infrared (4.25 microns) using a LiCor NDIR instrument. This is also a dual-cell device, in which the absorption caused by the ambient air sample is compared to that from a reference gas of known composition. Halocarbons are monitored with a custom-built gas chromatograph, using short, packed columns and small ovens, and HP micro-electron capture detectors. Ambient sample and standard will be run simultaneously on paired columns to reduce errors associated with drift in ECD response.

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