Overview and sample applications of SMILES and Odin-SMR retrievals of upper tropospheric humidity and cloud ice mass

Abstract

Abstract. Retrievals of cloud ice mass and humidity from the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) and the Odin-SMR (Sub-Millimetre Radiometer) limb sounder are presented and example applications of the data are given. SMILES data give an unprecedented view of the diurnal variation of cloud ice mass. Mean regional diurnal cycles are reported and compared to some global climate models. Some improvements in the models regarding diurnal timing and relative amplitude were noted, but the models' mean ice mass around 250 hPa is still low compared to the observations. The influence of the ENSO (El Niño-Southern Oscillation) state on the upper troposphere is demonstrated using 12 years of Odin-SMR data.The same retrieval scheme is applied for both sensors, and gives low systematic differences between the two data sets. A special feature of this Bayesian retrieval scheme, of Monte Carlo integration type, is that values are produced for all measurements but for some atmospheric states retrieved values only reflect a priori assumptions. However, this "allweather" capability allows a direct statistical comparison to model data, in contrast to many other satellite data sets. Another strength of the retrievals is the detailed treatment of "beam filling" that otherwise would cause large systematic biases for these passive cloud ice mass retrievals.The main retrieval inputs are spectra around 635/525 GHz from tangent altitudes below 8/9 km for SMILES/Odin-SMR, respectively. For both sensors, the data cover the upper troposphere between 30 • S and 30 • N. Humidity is reported as both relative humidity and volume mixing ratio. The vertical coverage of SMILES is restricted to a single layer, while Odin-SMR gives some profiling capability between 300 and 150 hPa. Ice mass is given as the partial ice water path above 260 hPa, but for Odin-SMR ice water content, estimates are also provided. Besides a smaller contrast between most dry and wet cases, the agreement with Aura MLS (Microwave Limb Sounder) humidity data is good. In terms of tropical mean humidity, all three data sets agree within 3.5 %RHi. Mean ice mass is about a factor of 2 lower compared to CloudSat. This deviation is caused by the fact that different particle size distributions are assumed, combined with saturation and a priori influences in the SMILES and Odin-SMR data.

Diurnal variation of tropospheric relative humidity in tropical region

“…Since Kottayil et al (2013) did not exclude the surface affected data, the results for the lower channels cannot be compared. Haffke and Magnusdottir (2015) reported a large inhomogeneity in the diurnal variation of precipitation which is consistent with the inhomogeneity we have found for relative humidity. Using Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar measurements, Biasutti et al (2011) reported a large difference between diurnal variation of precipitation over coastal lands (early afternoon peak) and near shores (early morning) influenced by the land/sea breeze.…”

Three Dimensional Radiative Effects in Passive Millimeter/Sub-Millimeter All-sky Observations

“…ARTS is a freely available software package, which has been designed for radiative transfer simulations for the mm and sub-mm spectral range, including polarization capabilities. ARTS has been comprehensively tested by comparison to a range of other MW radiative transfer models [59,60] and its performance has been demonstrated in various applications [11,12,14,44]. It can be operated in spherical geometry for 1D, 2D, and 3D atmospheres, and thus, it can be employed for a wide range of remote sensing applications.…”

“…Toward that end, the upcoming Ice Cloud Imager (ICI) instrument, which covers frequencies between 183.31 GHz and 668 GHz, on board the Meteorological Operational Satellite-Second Generation (Metop-SG) [9] operated by the European Organization of Meteorological Satellites (EUMETSAT), is going to fill this gap [10]. The performance of the sub-mm wavelengths in terms of retrieving ice properties has been manifested by airborne and limb sounding instruments; e.g., the International Submillimetre Airborne Radiometer (ISMAR) [11,12], the Compact Scanning Submillimeter-wave Imaging Radiometer (CoSSIR) [13], Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES), and the Odin-Sub-Millimetre Radiometer (Odin-SMR) [14]. Accordingly, ICI, with frequencies sensitive to the size, content, shape, and orientation of ice hydrometeors, aims at improving the representation of ice-containing clouds in NWP models.…”

Remote Sensing

“…The suitability of the submillimeter region for ice cloud retrievals has already been demonstrated using limb sounding instruments mainly devoted to stratospheric chemistry. Specifically, the Microwave Limb Sounder (MLS) (Waters et al 2006) with channels at 240 and 640 GHz and the submillimeter radiometer (SMR) on board the Odin satellite (Murtagh et al 2002) with channels between 500 and 650 GHz provide information on upper-tropospheric ice water content (Wu et al 2008, Eriksson et al 2014. The gap in terms of global ice cloud and light snow climatologies will be closed by the Ice Cloud Imager (ICI) on MetOP-SG to be launched 2021 (Bergada et al 2016).…”