We are delighted the announce the "Joint workshop on uncertainties at 183GHz", which is aimed at identifying possible explanations for biases observed between measured and simulated 183GHz data.
Radiometric observations at 183 GHz are one of the most important sources of humidity information for global and regional analysis, weather forecasts and climate monitoring. An understanding of their absolution calibration is important to their effective use, especially for climate applications, but also for weather forecasts where in many regions there is no good absolute reference for humidity.
Recent comparison of brightness temperatures measured by the SAPHIR instrument on Megha-Tropiques, ATMS on Suomi-NPP and MHS on Metop-A&B with values calculated using radiative transfer models such as RTTOV and ARTS, using both radiosonde and NWP short range forecasts input data, have shown biases in the wings of the 183 GHz line. Similar biases are also seen in other 183 GHz data such as MHS but the higher spectral sampling of SAPHIR and ATMS shows more clearly how the biases behave spectrally. A number of sources of the bias have been suggested, including spectroscopic errors, radiosonde bias, poor cloud screening and instrument calibration. It is proposed to hold a specialist workshop to examine these results and to make progress towards attribution of the bias.
The workshop will consider questions such as:
- How can we assess the absolute and relative accuracy of references such as radiosondes?
- How can we assess errors in the comparison between in-situ and space-borne measurements ?
- What uncertainty arises from the difference in the time/space scales of these measurements?
- What is the current best estimate of uncertainty in spectroscopic lineshapes and lineshape parameters ?
- What is the uncertainty arising from undetected clouds?
- How good is the absolute calibration of the instruments?
The workshop is formatted around a small number of introductory presentations followed by detailed working group discussions that will address errors and uncertainties for :
1) "in situ" water vapor measurements
2) spectroscopy and radiative transfer
3) water vapor analysis (NWP and geophysical products)
4) space-borne instruments
At the end, the workshop should lead to a summary of conclusions, recommendations and actions. These will be presented to the ITWG at the 20th International TOVS Study Conference, and summarized in a GEWEX newletter, from where selected recommendations will also be passed onto the International Radiation Commission and, if appropriate, the Coordinating Group on Meteorological Satellites.
The workshop is co-organised by LATMOS, ECMWF, Météo-France and IPSL under the auspices of both the ITWG and WCRP-GEWEX activities and with the sponsorship of Megha-Tropiques.
The organizing committee
Hélène Brogniez, Stephen English, Jean-François Mahfouf and Sophie Cloché
