Review of " Comparison of Global Datasets of Sodium Densities in the Mesosphere and Lower Thermosphere from GOMOS, SCIAMACHY and OSIRIS Measurements and WACCM Model Simulations from 2008 to 2012" by Langowski et al.

Abstract. During the last decade, multiple limb sounding satellites have measured the global sodium (Na) number densities in the mesosphere and lower thermosphere (MLT).Datasets are now available from GOMOS, SCIAMACHY (both on Envisat) and OSIRIS/Odin. Furthermore, global model simulations of the Na layer in the MLT simulated with WACCM-Na are available. In this paper, we compare these global datasets. Globally, there is an agreement in the observed and simulated monthly average of Na vertical column densities that were compared with each other. They show a clear seasonal cycle with a summer minimum most pronounced at the poles. They also show signs of a semi-annual oscillation in the equatorial region. The vertical column densities vary between 0.5 × 109 cm−2 to 7 × 109 cm−2 near the poles and between 3 × 109 cm−2 to 4 × 109 cm−2 at the equator. The phase of the seasonal cycle and semi-annual oscillation shows small differences between the different instruments. The full width at half maximum of the profiles is 10 to 16 km for most latitudes, but significantly smaller in the polar summer. The centroid altitudes of the measured sodium profiles range from 89 to 95 km, while the model shows on average 2 to 4 km lower centroid altitudes. This coincides with a 3 km lower mesopause altitude in the WACCM simulations compared to measurements, which may be the reason for the low centroid altitudes. Despite this global 2 to 4 km shift, the model captures latitudinal and temporal variations. The variation of the WACCM dataset during the year at different latitudes is similar to the one of the measurements. Furthermore, the differences between the measured profiles with different instruments and therefore different local times are also present in the model simulated profiles. This capturing of latitutinal and temporal variations is also found for the vertical column densities and profile widths.

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Comparison of global datasets of sodium densities in the mesosphere and lower thermosphere from GOMOS, SCIAMACHY and OSIRIS measurements and WACCM model simulations from 2008 to 2012

Atmospheric Measurement Techniques ◽

10.5194/amt-10-2989-2017 ◽

2017 ◽

Vol 10 (8) ◽

pp. 2989-3006 ◽

Cited By ~ 2

Author(s):

Martin P. Langowski ◽

Christian von Savigny ◽

John P. Burrows ◽

Didier Fussen ◽

Erin C. M. Dawkins ◽

...

Keyword(s):

Seasonal Cycle ◽

Climate Model ◽

Lower Thermosphere ◽

Temporal Variations ◽

Equatorial Region ◽

Local Times ◽

Vertical Column ◽

Model Simulations ◽

Mesosphere And Lower Thermosphere ◽

Scanning Imaging

Abstract. During the last decade, several limb sounding satellites have measured the global sodium (Na) number densities in the mesosphere and lower thermosphere (MLT). Datasets are now available from Global Ozone Monitoring by Occultation of Stars (GOMOS), the SCanning Imaging Absorption spectroMeter for Atmospheric CHartography (SCIAMACHY) (both on Envisat) and the Optical Spectrograph and InfraRed Imager System (OSIRIS) (on Odin). Furthermore, global model simulations of the Na layer in the MLT simulated by the Whole Atmosphere Community Climate Model, including the Na species (WACCM-Na), are available. In this paper, we compare these global datasets.The observed and simulated monthly averages of Na vertical column densities agree reasonably well with each other. They show a clear seasonal cycle with a summer minimum most pronounced at the poles. They also show signs of a semi-annual oscillation in the equatorial region. The vertical column densities vary from 0. 5 × 109 to 7 × 109 cm−2 near the poles and from 3 × 109 to 4 × 109 cm−2 at the Equator. The phase of the seasonal cycle and semi-annual oscillation shows small differences between the Na amounts retrieved from different instruments. The full width at half maximum of the profiles is 10 to 16 km for most latitudes, but significantly smaller in the polar summer. The centroid altitudes of the measured sodium profiles range from 89 to 95 km, whereas the model shows on average 2 to 4 km lower centroid altitudes. This may be explained by the mesopause being 3 km lower in the WACCM simulations than in measurements. Despite this global 2–4 km shift, the model captures well the latitudinal and temporal variations. The variation of the WACCM dataset during the year at different latitudes is similar to the one of the measurements. Furthermore, the differences between the measured profiles with different instruments and therefore different local times (LTs) are also present in the model-simulated profiles. This capturing of latitudinal and temporal variations is also found for the vertical column densities and profile widths.

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Large-Scale Waves in the Mesosphere and Lower Thermosphere Observed by SABER

Journal of the Atmospheric Sciences ◽

10.1175/jas3612.1 ◽

2005 ◽

Vol 62 (12) ◽

pp. 4384-4399 ◽

Cited By ~ 104

Author(s):

Rolando R. Garcia ◽

Ruth Lieberman ◽

James M. Russell ◽

Martin G. Mlynczak

Keyword(s):

Large Scale ◽

Middle Atmosphere ◽

Lower Thermosphere ◽

Normal Modes ◽

Zonal Winds ◽

Broadband Emission ◽

Summer Hemisphere ◽

Mean Structure ◽

Mesosphere And Lower Thermosphere ◽

The Tropics

Abstract Observations made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board NASA’s Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics (TIMED) satellite have been processed using Salby’s fast Fourier synoptic mapping (FFSM) algorithm. The mapped data provide a first synoptic look at the mean structure and traveling waves of the mesosphere and lower thermosphere (MLT) since the launch of the TIMED satellite in December 2001. The results show the presence of various wave modes in the MLT, which reach largest amplitude above the mesopause and include Kelvin and Rossby–gravity waves, eastward-propagating diurnal oscillations (“non-sun-synchronous tides”), and a set of quasi-normal modes associated with the so-called 2-day wave. The latter exhibits marked seasonal variability, attaining large amplitudes during the solstices and all but disappearing at the equinoxes. SABER data also show a strong quasi-stationary Rossby wave signal throughout the middle atmosphere of the winter hemisphere; the signal extends into the Tropics and even into the summer hemisphere in the MLT, suggesting ducting by westerly background zonal winds. At certain times of the year, the 5-day Rossby normal mode and the 4-day wave associated with instability of the polar night jet are also prominent in SABER data.

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