Abstract

The radar equation for the measurement of precipitation by SAR is identical to that for a conventional radar. The achievable synthetic beamwidth, β _s , is proportional to σ _v /U, the ratio of the spread of the precipitation Doppler spectrum to the platform velocity. Thus, a small β _s can be achieved only with small σ _v or from a fast-moving vehicle such as a spacecraft. Also, the along-track resolution is variable with σ _v and is not known. Nevertheless, the reflectivity is measured correctly. A possible approach to the measurement of σ _v is noted. The C-band SAR proposed for the Shuttle Imaging Radar-C (SIR-C) mission is capable of detecting a rain rate as small as 0.5 mm h⁻¹ at nadir when the beam is filled. Because the cross-track beam dimension is about 20 km wide, we suggest use of a high-resolution microwave radiometer to correct for the unfilled beam and the variation of gain across it. Alternatively, the cross-track dimension should be decreased to no more than about 5 km by increasing the antenna width and/or decreasing the wavelength.

Abstract

The characteristics of Great Lakes-induced storms and their cloud-to-ground (CG) lightning flashes are examined for four fall-winter seasons, beginning with the fall 1983-winter 1984 season. Satellite, surface, upper air, and lake temperature data were used in the analysis of the meteorological characteristics of the storms. The characteristics of the CG lightning flashes were recorded by the State University of New York at Albany Lightning Detection Network. During the 1983–87 period, the network covered lake Ontario and increasing portions of Lake Erie as a result of network expansion. Thus, both Lake Erie-induced and Lake Ontario-induced storms were selected for analysis. The storms that were examined produced three or more CG flashes on eight separate occasions. The earliest occurrence of a lake-induced storm with CG lightning was in mid-September, the latest in early December. These storms generally consisted of an enlarged, single band. Typically, only a few CG flashes were recorded per event. However, nearly 700 CG flashes were recorded during the very unusual 22–24 September 1983 event. A majority of all flashes were clustered over the eastern ends and eastern and southern shorelines of the lakes. Plateaus to the east of both lakes also appear to be favored locations for CG lightning activity. About 75% of all CG flashes lowered positive charge to ground, excluding the 22–24 September 1983 event when 70% of the flashes lowered negative charge to ground. Positive and negative flashes both were predominantly single-stroked. The median peak current of positive first return strokes was +79 kA for 22–24 September 1983 and +91 kA for the remaining seven storm periods. The corresponding median peak current values for negative first return strokes were −47 kA and −44 kA, respectively.

A summary is presented of the Surface Heat Budget of the Arctic Ocean (SHEBA) project, with a focus on the field experiment that was conducted from October 1997 to October 1998. The primary objective of the field work was to collect ocean, ice, and atmospheric datasets over a full annual cycle that could be used to understand the processes controlling surface heat exchanges—in particular, the ice–albedo feedback and cloud–radiation feedback. This information is being used to improve formulations of arctic ice–ocean–atmosphere processes in climate models and thereby improve simulations of present and future arctic climate. The experiment was deployed from an ice breaker that was frozen into the ice pack and allowed to drift for the duration of the experiment. This research platform allowed the use of an extensive suite of instruments that directly measured ocean, atmosphere, and ice properties from both the ship and the ice pack in the immediate vicinity of the ship. This summary describes the project goals, experimental design, instrumentation, and the resulting datasets. Examples of various data products available from the SHEBA project are presented.

Abstract

The National Aeronautics and Space Administration (NASA)’s Arctic Radiation-IceBridge Sea and Ice Experiment (ARISE) acquired unique aircraft data on atmospheric radiation and sea ice properties during the critical late summer to autumn sea ice minimum and commencement of refreezing. The C-130 aircraft flew 15 missions over the Beaufort Sea between 4 and 24 September 2014. ARISE deployed a shortwave and longwave broadband radiometer (BBR) system from the Naval Research Laboratory; a Solar Spectral Flux Radiometer (SSFR) from the University of Colorado Boulder; the Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) from the NASA Ames Research Center; cloud microprobes from the NASA Langley Research Center; and the Land, Vegetation and Ice Sensor (LVIS) laser altimeter system from the NASA Goddard Space Flight Center. These instruments sampled the radiant energy exchange between clouds and a variety of sea ice scenarios, including prior to and after refreezing began. The most critical and unique aspect of ARISE mission planning was to coordinate the flight tracks with NASA Cloud and the Earth’s Radiant Energy System (CERES) satellite sensor observations in such a way that satellite sensor angular dependence models and derived top-of-atmosphere fluxes could be validated against the aircraft data over large gridbox domains of order 100–200 km. This was accomplished over open ocean, over the marginal ice zone (MIZ), and over a region of heavy sea ice concentration, in cloudy and clear skies. ARISE data will be valuable to the community for providing better interpretation of satellite energy budget measurements in the Arctic and for process studies involving ice–cloud–atmosphere energy exchange during the sea ice transition period.