Radar observations of asteroid 1998 ML14

Abstract— Goldstone and Arecibo delay‐Doppler radar imaging of asteroid 1998 ML 14 shortly after its discovery reveals a 1 km diameter spheroid with prominent topography on one side and subdued topography on the other. The object's radar and optical properties are typical for S‐class near‐Earth asteroids. The gravitational slopes of a shape model derived from the images and assumed to have a uniform density are shallow, exceeding 30° over only 4% of the surface. If 1998 ML14's density distribution is uniform, then its orbital environment is similar to a planetary body with a spheroidal gravitational field and is relatively stable. Integration of a radar‐refined orbit reveals that the 1998 apparition was the asteroid's closest approach to Earth since at least 1100 and until 2283, when it approaches to within 2.4 lunar distances. Outside of that time interval, orbit uncertainties based on the present set of observations preclude reliable prediction.     

Canada-France-Hawaii Telescope's “redeye” infrared camera system: Array performance

The Canada-France-Hawaii Telescope (CFHT) has recently commissioned two facility infrared cameras for astronomical observations in the 1.0 to 2.5 micron region. These cameras use NICMOS3 256×256 pixel arrays fabricated from Hg:Cd:Te. We report here on array performance and discuss two unique features of these arrays, namely corner glow and residual images. We have developed techniques for reducing corner glow and a method of clearing residual image charge. We discuss our techniques and their side effects.     

Inference of Solar Magnetic Field Parameters from Data with Limited Wavelength Sampling

We investigate the diagnostic potential of polarimetric measurements with filtergraph instruments. Numerical simulations are used to explore the possibility of inferring the magnetic field vector, its filling factor, and the thermodynamics of model atmospheres when only a few wavelength measurements are available. These simulations assume the magnetic Sun to be represented by Milne–Eddington atmospheres. The results indicate that two wavelength measurements are insufficient to reliably determine the magnetic parameters, regardless of whether magnetograph techniques or least-squares fitting inversions are used. However, as few as four measurements analyzed with the inversion technique provide enough information to retrieve the intrinsic magnetic field with an accuracy better than 10% in most cases.     

The 13th and 14th Workshops on Antarctic Meteorology and Climate

1.Overview In July 2018,the Antarctic community came together to meet at the 13th Workshop on Antarctic Meteorology and Climate(WAMC)in Madison,Wisconsin,USA(Fig.1);and in the following year in June 2019,the 14th WAMC was held in Charleston,South Carolina,USA(Fig.2).With a growing history,the WAMC addresses the topics of Antarctic meteorology and climate(Kameda et al.,2008;Colwell et al.,2016;Lazzara et al.,2018)as well as weather-related issues of scientific and operational support.The workshops bring together researchers,operational forecasters,numerical modelers,observational specialists,and students.The themes of both workshops included Antarctic meteorological observations,Antarctic atmospheric numerical modeling,Antarctic meteorological and climate research,and Antarctic weather forecasting and operational services.The 2018 and 2019 WAMC were both followed by a one-day focus on the Year of Polar Prediction-Southern Hemisphere(YOPP-SH),when preparations and follow-up discussions were made with regard to the YOPP Special Observing Period from 16 November 2018 to 15 February 2019.     

Global distribution of the intensity and frequency of hourly precipitation and their responses to ENSO

Climate Dynamics - We investigate the global distribution of hourly precipitation and its connections with the El Niño–Southern Oscillation (ENSO) using both satellite precipitation...