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Ground-based high spectral resolution measurements of downwelling radiances from 800 to 1200 cm −1 were conducted between 20 January and 6 February 2008 within the scope of the SAMUM-2 field experiment. We infer the spectral signature of mixed biomass burning/mineral dust aerosols at the surface from these measurements and at top of the atmosphere from IASI observations. In a case study for a day characterized by the presence of high loads of both dust and biomass we attempt a closure with radiative transfer simulations assuming spherical particles. A detailed sensitivity analysis is performed to investigate the effect of uncertainties in the measurements ingested into the simulation on the simulated radiances. Distinct deviations between modelled and observed radiances are limited to a spectral region characterized by resonance bands in the refractive index. A comparison with results obtained during recent laboratory studies and field experiments reveals, that the deviations could be caused by the aerosol particles' non-sphericity, although an unequivocal discrimination from measurement uncertainties is not possible. Based on radiative transfer simulations we estimate the aerosol's direct radiative effect in the atmospheric window region to be 8 W m −2 at the surface and 1 W m −2 at top of the atmosphere.

T E L L U SThermal IR radiative properties of mixed mineral dust and biomass aerosol during SAMUM-2 A B S T R A C T Ground-based high spectral resolution measurements of downwelling radiances from 800 to 1200 cm −1 were conducted between 20 January and 6 February 2008 within the scope of the SAMUM-2 field experiment. We infer the spectral signature of mixed biomass burning/mineral dust aerosols at the surface from these measurements and at top of the atmosphere from IASI observations. In a case study for a day characterized by the presence of high loads of both dust and biomass we attempt a closure with radiative transfer simulations assuming spherical particles. A detailed sensitivity analysis is performed to investigate the effect of uncertainties in the measurements ingested into the simulation on the simulated radiances. Distinct deviations between modelled and observed radiances are limited to a spectral region characterized by resonance bands in the refractive index. A comparison with results obtained during recent laboratory studies and field experiments reveals, that the deviations could be caused by the aerosol particles' non-sphericity, although an unequivocal discrimination from measurement uncertainties is not possible. Based on radiative transfer simulations we estimate the aerosol's direct radiative effect in the atmospheric window region to be 8 W m −2 at the surface and 1 W m −2 at top of the atmosphere.

A submillimeter heterodyne spectrometer employing a superconducting local oscillator is demonstrated for the first time. The sensor chip comprises a quasioptical double-dipole lens-antenna SIS mixer (RX = 250 K at 380 GHz), a Josephson flux-flow oscillator and a SIS harmonic mixer. Room temperature PLL electronics is used with a reference source at 10 GHz. The PLL bandwidth of 10 MHz and the hold range of 3 GHz are estimated for locking at 32-th harmonic of the reference source. The spectral resolution better than 1 MHz and broadening effect of a spectral line of SO 2 gas at 326867 MHz are measured with a laboratory gas cell at 300 K at pressure 0.03-0.3 mbar using acousto-optical spectrometer.

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