Figure 1 - uploaded by D. Cimini
Content may be subject to copyright.
Atmospheric opacity for Arctic conditions. Vertical lines indicate the spectral locations of GSR (cyan) and MWR (red) channels. The red-filled boxes indicate the spectral range spanned by MWRP.
Context in source publication
Context 1
... and a twelve-channel microwave radiometer profiler (MWRP, channels at 22.235, 23.035, 23.835, 26.235, 30.0, 51.25, 52.28, 53.85, 54.94, 56.66, 57.29, and 58.8 GHz). The spectral locations of GSR, MWR, and MWRP channels are shown in Figure 1, together with an atmospheric opacity (τ) spectrum typical of Arctic conditions. Note that the opacity for the mm and submm channels is one-two orders of magnitude larger than for the centimeter-wavelength (20-30 GHz) channels of the MWR and MWRP. ...
Similar publications
Citations
... Therefore, a more accurate reference standard is needed to scale the radiosonde water vapor observations in the dry Arctic. The 183.31 GHz water vapor line is significantly stronger than the 22.2 GHz water vapor absorption feature (Fig 4), and thus microwave radiometers that observe near the former frequency are approximately 70 times more sensitive to PWV than the MWR [Cimini et al. 2006a]. The ARM program has recently benefited from a DOE SBIR effort, which resulted in an automated 183-GHz radiometer being permanently deployed at the NSA site [Cadeddu et al. 2006]. ...
Radiative cooling and heating in the mid-to-upper troposphere contribute significantly to the dynamical processes and radiative balance that regulate Earth's climate. In the longwave, the dominant agent of this radiative cooling is water vapor. Due to the much greater abundances of this gas at lower levels of the atmosphere, the spectral regions in which the mid-to-upper tropospheric cooling occurs are opaque when viewed from the vast majority of surface locations. The opacity of the lower atmosphere is a formidable obstacle in evaluating radiative processes important in the mid-to-upper troposphere from the surface; however, an even more substantial obstacle has been the lack of radiometric instrumentation in the most critical spectral region for these processes, the far-infrared (λ > 15 µm). The recent development of a new generation of instruments for the measurement of spectral radiation in the far-infrared has provided the capability to rectify this state of affairs. These instruments will allow the evaluation of radiatively important processes in the mid-to-upper troposphere. This presents ARM with a terrific opportunity to contribute substantially to the improvement of the parameterization of these crucial radiative processes in climate simulations. We propose to conduct the Radiative Heating in Underexplored Bands Campaign (RHUBC, pronounced "roobik") from 22 February to 14 March 2007 at the NSA site in Barrow. This experiment will make detailed observations of the downwelling infrared radiation in the 17-100 µm (100-600 cm -1) rotational and 6.7 µm (1350-1850 cm -1) υ 2 water vapor bands. Both of these spectral bands are underexplored because they are normally opaque at the surface due to strong absorption by water vapor, and hence the radiative heating in these bands is uncertain. High-spectral-resolution observations will be collected by three state-of-the-art Fourier Transform Spectrometers (FTS): the ARM AERI-ER (400 -3000 cm -1), the NASA/LaRC FIRST (20 -1600 cm -1), and the Imperial College TAFTS (80 -650 cm -1). During the proposed IOP period, the precipitable water vapor (PWV) is small (typically less than 3 mm) and thus important parts of the rotational and υ 2 water vapor bands will be semi-transparent, and the incidence of low stratus clouds is at a minimum (~ 40-50%).
At frequencies of between 100 GHz and 30 THz, propagation conditions are severely affected by the influence of the composition and phenomena of the troposphere. This paper focuses on the use of radiometric measurements to estimate attenuation at 100 and 300GHz, considering non-scattering scenarios, in which the main contributions are given by atmospheric gases and non-rainy clouds. These techniques allow the estimation of the absorption loss through the entire atmosphere, without the need for a signal source situated in a satellite or a high altitude aircraft. On the basis of well-accepted absorption models, the results of calculating gaseous, cloud, and total attenuation using 3-year meteorological data from Madrid, Spain, are detailed, as well as estimates of the expected values of the sky brightness temperature as measured by the radiometer. Finally, based on the results obtained, a discussion on the use of radiometric measurements at both frequencies is presented, in connection with an experimental campaign currently under preparation.
