J. Tuovinen

A Climatological Comparison of Radar and Ground Observations of Hail in Finland

Abstract Two approaches to producing a hail climatology for Finland are compared. The first approach is based on 70 yr of hail reports from different sources (newspapers, storm spotters, and other volunteers). The second is derived primarily from radar data. It is shown that a selection of newspaper articles of hail damage covering a period of 70 yr provides a good overview of the typical monthly and diurnal distribution of hail occurrence over the country. Radar data covering five summers (2001–05) provide another data source, but with different potential sources of errors. The two distinct methods compared in this paper give roughly the same results in describing the hail climatology of Finland, which gives additional confidence in each of the methods. On the basis of both methods, most hailstones are observed in the afternoon, 1400–1600 local time. The hail “season” extends from May to early September with maximum occurrences in June, July, and August. This means that hail is most frequently observed w...

Design, development, and verification of the Planck Low Frequency Instrument 70 GHz Front-End and Back-End Modules

70 GHz radiometer front-end and back-end modules for the Low Frequency Instrument of the European Space Agencys Planck Mission were built and tested. The operating principles and the design details of the mechanical structures are described along with the key InP MMIC low noise amplifiers and phase switches of the units. The units were tested in specially designed cryogenic vacuum chambers capable of producing the operating conditions required for Planck radiometers, specifically, a physical temperature of 20 K for the front-end modules, 300 K for the back-end modules and 4 K for the reference signal sources. Test results of the low noise amplifiers and phase switches, the front and back-end modules, and the combined results of both modules are discussed. At 70 GHz frequency, the system noise temperature of the front and back end is 28 K; the effective bandwidth 16 GHz, and the 1/f spectrum knee frequency is 38 mHz.The test results indicate state-of-the-art performance at 70 GHz frequency and fulfil the Planck performance requirements.

Thermal susceptibility of the Planck-LFI receivers

This paper describes the impact of the Planck Low Frequency Instrument front end physical temperature fluctuations on the output signal. The origin of thermal instabilities in the instrument are discussed, and an analytical model of their propagation and impact on the receivers signal is described. The experimental test setup dedicated to evaluate these effects during the instrument ground calibration is reported together with data analysis methods. Finally, main results obtained are discussed and compared to the requirements.