A new millimeter-wave cloud radar (MMCR) has been designed to provide detailed, long-term observations of nonprecipitating and weakly precipitating clouds at Cloud and Radiation Testbed (CART) sites of the Department of Energy's Atmospheric Radiation Measurement (ARM) program. Scientific requirements included excellent sensitivity and vertical resolution to detect weak and thin multiple layers of ice and liquid water clouds over the sites and longterm, unattended operations in remote locales. In response to these requirements, the innovative radar design features a vertically pointing, single-polarization, Doppler system operating at 35 GHz (K a band). It uses a low-peak-power transmitter for long-term reliability and high-gain antenna and pulse-compressed waveforms to maximize sensitivity and resolution. The radar uses the same kind of signal processor as that used in commercial wind profilers. The first MMCR began operations at the CART in northern Oklahoma in late 1996 and has operated continuously there for thousands of hours. It routinely provides remarkably detailed images of the ever-changing cloud structure and kinematics over this densely instrumented site. Examples of the data are presented. The radar measurements will greatly improve quantitative documentation of cloud conditions over the CART sites and will bolster ARM research to understand how clouds impact climate through their effects on radiative transfer. Millimeter-wave radars such as the MMCR also have potential applications in the fields of aviation weather, weather modification, and basic cloud physics research.

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Abstract. Strong internal waves (IW) in the form of soliton groups were observed off the Oregon coast with in situ and remote sensors, including shore-based X band and K a band Doppler radars and an airborne microwave radiometer operating at 37 GHz. Here we analyze the relationships between oceanic isotherm vertical displacements, internal currents, and radar backscatter cross sections, along with Doppler velocity signals at horizontal (HH) and vertical (VV) polarizations, and 37-GHz brightness temperatures measured at intermediate incidence angles from an airship. Analysis of these observations shows that (1) the horizontal spatial structure of the IW field depends on whether it is forced by a strong (spring) tide or weak (neap) tide; (2) while both HH and VV are strongly modulated by IWs, the modulation depth of HH always exceeds that of VV, and they both increase with the IW amplitude; (3) 37-GHz brightness temperature modulations were in phase with radar signal modulations; and (4) the phase of radar signal modulation with respect to the IW is such that the minimum radar signal intensity and lowest microwave brightness temperature lie close to the maximum of the IW thermocline depression or, equivalently, the horizontal current excursion near the surface. This last observation conflicts with the expectation that the highest backscattered signal would be found near the region of greatest surface strain rate (the surface current gradient). Existing theoretical models are briefly reviewed for interactions between the IW field and the intensity of short gravity-capillary waves that might be responsible for this behavior. Introduction

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