2 research outputs found
Bias and Drift of the Medium-Range Decadal Climate Prediction System (MiKlip) validated by European Radiosonde Data
Quality controlled and homogenized radiosonde observations have been used to
validate decadal hindcasts of the MPI-Earth-System-Model for Europe (excl.
some Eastern European countries). Simulated temperatures have a cold bias of 1
to 4 K, increasing with height throughout the free troposphere over Europe.
This implies that the simulated troposphere is less stable than observed by
the radiosondes over Europe. Simulated relative humidity is 10 to 40 % higher
than observed. Part of the humidity bias, 10 to 25 % relative humidity, is due
to the simulated lower temperature, but the remainder indicates that modelled
water vapour pressure is too high in the free troposphere above Europe. After
full-field initialization with oceanic state, the atmospheric temperature bias
changes over the first couple of years, with a relaxation time of 5 years near
the surface (850 hPa) and less than 1 year near the tropopause (200 hPa).
Anomaly correlations, mean-square error and logarithmic ensemble spread score
indicate small improvements in hindcasted tropospheric temperatures over
Europe when going from ocean anomaly initialisation to ocean anomaly
initialisation plus full field atmospheric initialisation, and then to full
field ocean initialisation plus full field atmospheric initialisation. In the
stratosphere, these changes have little effect. For humidity, correlations and
skill scores are much poorer, and little can be said about changes over Europe
due to different initializations
Aerosol backscatter profiles from ceilometers: validation of water vapor correction in the framework of CeiLinEx2015
With the rapidly growing number of automated single-wavelength backscatter lidars (ceilometers), their potential benefit for aerosol remote sensing received considerable scientific attention. When studying the accuracy of retrieved particle backscatter coefficients, it must be considered that most of the ceilometers are influenced by water vapor absorption in the spectral range around 910 nm. In the literature methodologies have been proposed to correct for this effect;however, a validation was not yet performed. In the framework of the ceilometer intercomparison campaign CeiLinEx2015 in Lindenberg, Germany, hosted by the German Weather Service, it was possible to tackle this open issue. Ceilometers from Lufft (CHM15k and CHM15kx, operating at 1064 nm), from Vaisala (CL51 and CL31) and from Campbell Scientific (CS135), all operating at a wavelength of approximately 910 nm, were deployed together with a multi-wavelength research lidar (RALPH) that served as a reference. In this paper the validation of the water vapor correction is performed by comparing ceilometer backscatter signals with measurements of the reference system extrapolated to the water vapor regime. One inherent problem of the validation is the spectral extrapolation of particle optical properties. For this purpose AERONET measurements and inversions of RALPH signals were used. Another issue is that the vertical range where validation is possible is limited to the upper part of the mixing layer due to incomplete overlap and the generally low signal-to-noise ratio and signal artifacts above that layer. Our intercomparisons show that the water vapor correction leads to quite a good agreement between the extrapolated reference signal and the measurements in the case of CL51 ceilometers at one or more wavelengths in the specified range of the laser diode's emission. This ambiguity is due to the similar effective water vapor transmission at several wavelengths. In the case of CL31 and CS135 ceilometers the validation was not always successful. That suggests that error sources beyond the water vapor absorption might be dominant. For future applications we recommend monitoring the emitted wavelength and providing "dark" measurements on a regular basis