In June 1994 the Monterey Area Ship Track (MAST) experiment was conducted off the coast of California to investigate the processes behind anthropogenic modification of cloud albedo. The motivation for the MAST experiment is described here, as well as details of the experimental design. Measurement platforms and strategies are explained, and a summary of experiment operations is presented. The experiment produced the largest dataset to date of direct measurements of the effects of ships on the microphysics and radiative properties of marine stratocumulus clouds as an analog for the indirect effects of anthropogenic pollution on cloud albedo.

A mobile, phased-array Doppler radar, the Mobile Weather Radar, 2005 X-band, Phased Array (MWR-05XP), has been used since 2007 to obtain data in supercells and tornadoes. Rapidly updating, volumetric data of tornadic vortex signatures (TVSs) associated with four tornadoes are used to investigate the time-height evolution of TVS intensity, position, and dissipation up through storm midlevels. Both TVS intensity and position were highly variable in time and height even during tornado mature phases. In one case, a TVS associated with a tornado dissipated aloft and a second TVS formed shortly thereafter while there was one continuous TVS near the ground. In a second case, the TVS associated with a long-lived, violent tornado merged with a second TVS (likely a second cyclonic tornado) causing the original TVS to strengthen. TVS dissipation occurred first at a height of ;1.5 km AGL and then at progressively higher levels in two cases; TVS dissipation occurred last in the lowest 1 km in three cases examined. Possible explanations are provided for the unsteady nature of TVS intensity and a conceptual model is presented for the initial dissipation of TVSs at ;1.5 km AGL.

Observations from a hybrid phased-array Doppler radar, the Mobile Weather Radar, 2005 X-band, Phased Array (MWR-05XP), were used to investigate the vertical development of tornadic vortex signatures (TVSs) during supercell tornadogenesis. Data with volumetric update times of ∼10 s, an order of magnitude better than that of most other mobile Doppler radars, were obtained up to storm midlevels during the formation of three tornadoes. It is found that TVSs formed upward with time during tornadogenesis for two cases. In a third case, missing low-level data prevented a complete time–height analysis of TVS development; however, TVS formation occurred first near the ground and then at storm midlevels several minutes later. These results are consistent with the small number of volumetric mobile Doppler radar tornadogenesis cases from the past ∼10 years, but counter to studies prior to that, in which a descending TVS was observed in roughly half of tornado cases utilizing Weather Surveillance Radar-1988 Doppler (WSR-88D) data. A comparative example is used to examine the possible effects relatively long WSR-88D volumetric update times have on determining the mode of tornadogenesis.

In a recent field experiment a truck-based, rapid scan, agile-beam Doppler radar probed severe convective storms and tornadoes on very short time scales, at relatively close range. , the advective time scale is only 10 s. Bluestein et al. (2003; their Figs. 10 and 11) showed how even when the reflectivity and Doppler wind field in a tornado at low levels is viewed every ~15 s, not all the evolution is captured.In a supercell having updrafts of ~50 m s −1 (e.g., Weisman and Klemp 1984, their Fig. 5; Bluestein et al. 1988, their Fig. 15), vortices, cloud particles, small hydrometeors, etc., can be advected upward ~5 km, almost half the depth of the parent storm in just ~100 s (a few min). Trapp et al. (1999) found after inspecting Weather Surveillance Radar-1988 Doppler (WSR-88D) volume scans that some tornadic vortex signatures descend, whereas others 

The High-Definition Sounding System (HDSS) is an automated system deploying the expendable digital dropsonde (XDD) designed to measure wind and pressure–temperature–humidity (PTH) profiles, and skin sea surface temperature (SST) within and around tropical cyclones (TCs) and other high-impact weather events needing high sampling density. Three experiments were conducted to validate the XDD. On two successive days off the California coast, 10 XDDs and 14 Vaisala RD-94s were deployed from the navy’s Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft over offshore buoys. The Twin Otter made spiral descents from 4 km to 60 m at the same descent rate as the sondes. Differences between successive XDD and RD-94 profiles due to true meteorological variability were on the same order as the profile differences between the spirals, XDDs, and RD-94s. XDD SST measured via infrared microradiometer, referred to as infrared skin SST (SSTir), and surface wind measurements were within 0.5°C and 1.5 m s−1, respectively, of buoy and Twin Otter values. A NASA DC-8 flight launched six XDDs from 12 km between ex-TC Cosme and the Baja California coast. Repeatability was shown with good agreement between features in successive profiles. XDD SSTir measurements from 18° to 28°C and surface winds agreed well with drifting buoy- and satellite-derived estimates. Excellent agreement was found between PTH and wind profiles measured by XDDs deployed from a NASA WB-57 at 18-km altitude offshore from the Texas coast and NWS radiosonde profiles from Brownsville and Corpus Christi, Texas. Successful XDD profiles were obtained in the clear and within precipitation over an offshore squall line.

Measurements of solar and infrared irradiance by instruments rigidly mounted to an aircraft have historically been plagued by the introduction of offsets and fluctuations into the data that are solely due to the pitch and roll movements of the aircraft. The Stabilized Radiometer Platform (STRAP) was developed to address this problem. Mounted on top of an aircraft and utilizing a self-contained, coupled Inertial Navigation System–GPS, STRAP actively keeps a set of uplooking radiometers horizontally level to within ±0.02° for aircraft pitch and roll angles of up to approximately ±10°. The system update rate of 100 Hz compensates for most pitch and roll changes experienced in normal flight and in turbulence. STRAP was mounted on a Twin Otter aircraft and its performance evaluated during normal flight and during a series of flight maneuvers designed to test the accuracy, range, and robustness of the platform. The measurements from an identical pair of solar pyranometers—one mounted on STRAP and the other rigidly mounted nearby directly to the aircraft—are compared to illustrate the accuracy and capability of the new platform. Results show that STRAP can keep radiometers level within the specified pitch and roll range, that it is able to recover from flight maneuvers outside of this range, and that it greatly increases the quantity of useful radiometer data from any given flight. Of particular note, STRAP now allows accurate measurements of the downwelling solar irradiance during spiral ascents or descents of the aircraft, greatly expanding the utility of aircraft radiometer measurements.

A remotely piloted aircraft research facility is described that will provide new capabilities for atmospheric and oceanographic measurements. The aircraft can fly up to 24 h over remote ocean regions, at low or high altitude, and in various other challenging mission scenarios. The aircraft will fly research missions at speeds of 40 m s-1 and provide high spatial resolution measurements. Data will be transmitted in real time to a ground station for analysis and decision-making purposes. The facility will expand the opportunities for universities to participate in field measurement programs. l.lntroductionThe Office of Naval Research (ONR), the Naval Postgraduate School, California Institute of Technology, and Princeton University are developing a joint research facility, the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRP AS), to support scientific research and technology development. CIRP AS is developing and will operate three types of remotely piloted aircraft (RP A) that can support many traditional atmospheric or oceanographic measurements, as well as unique measurement strategies that would be difficult or impossible with a manned aircraft. This paper describes CIRPAS and the flight and research capabilities of the RP As and presents a series of proposed applications. We list a set of research activities that we anticipate will make significant advances under CIRP AS. The list comes from numerous discussions with the science and technology develop- The CIRPAS conceptThe main goal of CIRP AS is to expand investigator access to airborne and remote sensing data by providing state-of-the-art capabilities at the lowest possible costs. CIRPAS will provide investigators with new capabilities for long-duration observations at very high or low altitudes. CIRP AS platforms will operate at uniquely low air speeds allowing highresolution in situ observations. Low operational cost of the CIRP AS platfonris will be achieved primarily by innovative use of small aircraft. Use of a satellite communications and data management system, and support of scientific instrument miniaturization, will allow a much smaller aircraft to perform similarly to traditional larger aircraft. Use of a satellite data link provides a "virtual" in-flight working environment through real-time access to scientific data and flight attitude information. A satellite data link will allow broader user access to flight operations, ranging from remote terminals over the modem link to group operations in the flight ground control facility. New technologies and concepts are under development to miniaturize airborne atmospheric and oceanographic instruments without reducing instrument fidelity or resolution. 2691

Fig. 1. The CIRPAS UV-18A Twin Otter turboprop research aircraft. This twin turboprop Short Takeoff and Landing (STOL) aircraft can cruise at low speeds for long durations over the ocean with a maximum endurance of 8 hours, maximum altitude of 7600 m, 35-80 m/s operational speed range, 200 amps of payload power, and an approximately 2400 kg useful load. Original color