Modeling the Zeeman effect in high-altitude SSMIS channels for numerical weather prediction profiles: comparing a fast model and a line-by-line model

Abstract

Abstract. We present a comparison of a reference and a fast radiative transfer model using numerical weather prediction profiles for the Zeeman-affected high-altitude Special Sensor Microwave Imager/Sounder channels 19-22. We find that the models agree well for channels 21 and 22 compared to the channels' system noise temperatures (1.9 and 1.3 K, respectively) and the expected profile errors at the affected altitudes (estimated to be around 5 K). For channel 22 there is a 0.5 K average difference between the models, with a standard deviation of 0.24 K for the full set of atmospheric profiles. Concerning the same channel, there is 1.2 K on average between the fast model and the sensor measurement, with 1.4 K standard deviation. For channel 21 there is a 0.9 K average difference between the models, with a standard deviation of 0.56 K. Regarding the same channel, there is 1.3 K on average between the fast model and the sensor measurement, with 2.4 K standard deviation. We consider the relatively small model differences as a validation of the fast Zeeman effect scheme for these channels. Both channels 19 and 20 have smaller average differences between the models (at below 0.2 K) and smaller standard deviations (at below 0.4 K) when both models use a two-dimensional magnetic field profile. However, when the reference model is switched to using a full three-dimensional magnetic field profile, the standard deviation to the fast model is increased to almost 2 K due to viewing geometry dependencies, causing up to ±7 K differences near the equator. The average differences between the two models remain small despite changing magnetic field configurations. We are unable to compare channels 19 and 20 to sensor measurements due to limited altitude range of the numerical weather prediction profiles. We recommended that numerical weather prediction software using the fast model takes the available fast Zeeman scheme into account for data assimilation of the affected sensor channels to better constrain the upper atmospheric temperatures.

Martian magnetism with orbiting sub-millimeter sensor: simulated retrieval system

“…The Zeeman effect module of ARTS (Larsson et al, 2014) is applied for these calculations to simulate the left circular polarization component as observed by the simulated sensor for a 20 MHz passband of 201 channels of 100 kHz Gaussian shape surrounding the central absorption line at 368 GHz. The ARTS Zeeman effect module has been validated using ground-based measurements (Navas-Guzmán et al, 2015) and by comparisons with meteorological satellite measurements (Larsson et al, 2016), in applications considering the radiation in different states of polarization. Circular polarization is noticeably more influenced by the magnetic field than linear polarization, and 10 MHz on both sides of the line captures most of the information given by the Zeeman effect.…”

ARTS, the atmospheric radiative transfer simulator – version 2.2, the planetary toolbox edition

“…The ARTS Zeeman calculations have been validated in some studies so far: Navas-Guzmán et al (2015) simulated groundbased observations of mesospheric molecular oxygen spectra in linear polarization for several observational directions, and found good agreement with observations; Larsson et al (2016) compared the ARTS simulations for a down-looking meteo-25 rological sensor to observations and to another, stronger parameterised Zeeman model. The module has also been applied to theoretical studies on mapping Martian surface magnetism (Larsson et al, 2013(Larsson et al, , 2017.…”

“…The method has been validated against observations in uplooking (Navas- Guzmán et al, 2015) and downlooking (Larsson et al, 2016) geometry, and also has already been employed for some sensitivity and retrieval simulation studies (Larsson et al, 2013(Larsson et al, , 2017.…”

ARTS, the Atmospheric Radiative Transfer Simulator – version 2.2, the planetary toolbox edition

“…The ARTS oxygen Zeeman calculations have been validated in some studies so far: Navas-Guzmán et al (2015) simulated ground-based observations of mesospheric molecular oxygen spectra in linear polarization for several observational directions and found good agreement with observations; Larsson et al (2016) compared the ARTS simulations for a down-looking meteorological sensor to observations and to another, stronger parameterized Zeeman model. The module has also been applied to theoretical studies on mapping Martian surface magnetism (Larsson et al, 2013(Larsson et al, , 2017.…”

“…This has benefited greatly from the experience gathered with the last important addition that has to be mentioned here: the capability to simulate oxygen Zeeman splitting in a physically rigorous way, which is also handled by a Stokes vector formalism, described in Larsson et al (2014) and Larsson (2014). The method has been validated against observations in uplooking (Navas- Guzmán et al, 2015) and down-looking (Larsson et al, 2016) geometry and has also already been employed for some sensitivity and retrieval simulation studies (Larsson et al, 2013(Larsson et al, , 2017.…”