A new remote sensing concept extrapolated from the GPS occultation concept is presented in which the signal frequencies are chosen to determine atmospheric water, temperature, and the geopotential of atmospheric pressure surfaces. Using frequencies near the 22-and 183-GHz water lines allows not only the speed of light to be derived as a GPS occultation but also derivation of profiles of absorption caused by atmospheric water. Given the additional water information, moisture and temperature as well as the geopotential of pressure surfaces can be separated and solved for. Error covariance results indicate that the accuracies of individual water profiles will be 0.5%-3% extending from roughly 1-75-km altitude. Temperature accuracies of individual profiles will be sub-Kelvin from ϳ1to 70-km altitude depending on latitude and season. Accuracies of geopotential heights of pressure will be 10-20 m from the surface to 60-km altitude. These errors are random such that climatological averages derived from this data will be significantly more accurate. Owing to the limb-viewing geometry, the along-track resolution is comparable to the 200-300 km of the GPS occultation observations, but the shorter 22-and 183-GHz wavelengths improve the diffraction-limited vertical resolution to 100-300 m. The technique can be also used to determine profiles of other atmospheric constituents such as upper-tropospheric and stratospheric ozone by using frequencies near strong lines of that constituent. The combined dynamic range, accuracy, vertical resolution, and ability to penetrate clouds far surpass that of any present or planned satellite sensors. A constellation of such sensors would provide an all-weather, global remote sensing capability including full sampling of the diurnal cycle for process studies related to water, climate research, and weather prediction in general.

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The profiles of marine boundary layer (MBL) cloud and drizzle microphysical properties are important for studying the cloud-to-rain conversion and growth processes in MBL clouds. However, it is challenging to simultaneously retrieve both cloud and drizzle microphysical properties within an MBL cloud layer using ground-based observations. In this study, methods were developed to first decompose drizzle and cloud reflectivity in MBL clouds from Atmospheric Radiation Measurement cloud radar reflectivity measurements and then simultaneously retrieve cloud and drizzle microphysical properties during the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) campaign. These retrieved microphysical properties, such as cloud and drizzle particle size (r c and r m,d ), their number concentration (N c and N d ) and liquid water content (LWC c and LWC d ), have been validated by aircraft in situ measurements during ACE-ENA (~158 hr of aircraft data). The mean surface retrieved (in situ measured) r c , N c , and LWC c are 10.9 μm (11.8 μm), 70 cm −3 (60 cm −3 ), and 0.21 g m −3 (0.22 g m −3 ), respectively. For drizzle microphysical properties, the retrieved (in situ measured) r d , N d , and LWC d are 44.9 μm (45.1 μm), 0.07 cm −3 (0.08 cm −3 ), and 0.052 g m −3 (0.066 g m −3 ), respectively. Treating the aircraft in situ measurements as truth, the estimated median retrieval errors are~15% for r c ,~35% for N c ,~30% for LWC c and r d , and~50% for N d and LWC d . The findings from this study will provide insightful information for improving our understanding of warm rain processes, as well as for improving model simulations. More studies are required over other climatic regions. Key Points: • New methods are developed to simultaneously retrieve MBL cloud and drizzle microphysical properties in drizzling clouds • The retrievals are validated with in situ measurements with errors of 15% for r c , 35% for N c , 30% for LWC c and r m,d , and 50% for N d and LWC d . (2020). Profiles of MBL cloud and drizzle microphysical properties retrieved from ground-based observations and validated by aircraft in situ measurements over the Azores.

Abstract. We present initial results from testing a new remote sensing system called the Active Temperature, Ozone and Moisture Microwave Spectrometer (ATOMMS). ATOMMS is designed as a satellite-to-satellite occultation system for monitoring climate. We are developing the prototype instrument for an aircraft to aircraft occultation demonstration. Here we focus on field testing of the ATOMMS instrument, in particular the remote sensing of water by measuring the attenuation caused by the 22 GHz and 183 GHz water absorption lines.Our measurements of the 183 GHz line spectrum along an 820 m path revealed that the AM 6.2 spectroscopic model provdes a much better match to the observed spectrum than the MPM93 model. These comparisons also indicate that errors in the ATOMMS amplitude measurements are about 0.3 %. Pressure sensitivity bodes well for ATOMMS as a climate instrument. Comparisons with a hygrometer revealed consistency at the 0.05 mb level, which is about 1 % of the absolute humidity.Initial measurements of absorption by the 22 GHz line made along a 5.4 km path between two mountaintops captured a large increase in water vapor similar to that measured by several nearby hygrometers. A storm passage between the two instruments yielded our first measurements of extinction by rain and cloud droplets. Comparisons of ATOMMS 1.5 mm opacity measurements with measured visible opacity and backscatter from a weather radar revealed features simultaneously evident in all three datasets confirming the ATOMMS measurements. The combined ATOMMS, radar and visible information revealed the evolution of rain and cloud amounts along the signal path during the passage of the storm. The derived average cloud water content reached typical continental cloud amounts. These results demonstrated a significant portion of the information content of ATOMMS and its ability to penetrate through clouds and rain which is critical to its all-weather, climate monitoring capability.

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