Assessing the ability to derive rates of polar middle-atmospheric descent using trace gas measurements from remote sensors

Abstract

Abstract. We investigate the reliability of using trace gas measurements from remote sensing instruments to infer polar atmospheric descent rates during winter within 46-86 km altitude. Using output from the Specified Dynamics Whole Atmosphere Community Climate Model (SD-WACCM) between 2008 and 2014, tendencies of carbon monoxide (CO) volume mixing ratios (VMRs) are used to assess a common assumption of dominant vertical advection of tracers during polar winter. The results show that dynamical processes other than vertical advection are not negligible, meaning that the transport rates derived from trace gas measurements do not represent the mean descent of the atmosphere. The relative importance of vertical advection is lessened, and exceeded by other processes, during periods directly before and after a sudden stratospheric warming, mainly due to an increase in eddy transport. It was also found that CO chemistry cannot be ignored in the mesosphere due to the night-time layer of OH at approximately 80 km altitude. CO VMR profiles from the Kiruna Microwave Radiometer and the Microwave Limb Sounder were compared to SD-WACCM output, and show good agreement on daily and seasonal timescales. SD-WACCM CO profiles are combined with the CO tendencies to estimate errors involved in calculating the mean descent of the atmosphere from remote sensing measurements. The results indicate errors on the same scale as the calculated descent rates, and that the method is prone to a misinterpretation of the direction of air motion. The "true" rate of atmospheric descent is seen to be masked by processes, other than vertical advection, that affect CO. We suggest an alternative definition of the rate calculated using remote sensing measurements: not as the mean descent of the atmosphere, but as an effective rate of vertical transport for the trace gas under observation.

Winter 2018 major sudden stratospheric warming impact on midlatitude mesosphere from microwave radiometer measurements

“…2a). Our velocity estimates are similar to those of Salmi et al (2011), who found that mesospheric NO x anomalies during the major SSW of 2009 were transported from 80 to 55 km in about 40 d, i.e., with a velocity of −600 m d −1 .…”

“…Mesospheric responses to the SSW are observed as enhancement in planetary wave amplitude, zonal wind reversal, and significant air cooling (Shepherd et al, 2014;Zülicke and Becker, 2013;Stray et al, 2015;Zülicke et al, 2018); substantial depletion of the metal layers (Feng et al, 2017;Gardner, 2018); and mesosphere-to-stratosphere descent of trace species (Manney et al, 2009;Salmi et al, 2011). The SSW events are also accompanied by the rapid descent of the stratopause into the stratosphere at the SSW onset, followed by formation of the elevated stratopause in the lower mesosphere and gradual stratopause lowering toward its typical position in the SSW recovery phase (Manney et al, 2009;Chandran et al, 2011;Salmi et al, 2011;Tomikawa et al, 2012;Limpasuvan et al, 2016;Orsolini et al, 2010Orsolini et al, , 2017. The elevated stratopause events provide evidence for the coupling between the stratosphere and the mesosphere.…”

Connections Between Stratospheric Ozone Concentrations Over the Arctic and Sea Surface Temperatures in the North Pacific

“…These results suggest that the BDC terms related to the North Pacific SSTAs play a key part in determining the changes in ozone concentration, but also that the eddy transport and chemical processes related to the SSTAs in the North Pacific may modulate the concentration of ozone. The residual term actually contains three terms that modify the ozone concentration: chemical production; molecular diffusion; and gravity waves (Ryan et al, ). Ryan et al () showed that the magnitudes of the gravity wave and molecular diffusion terms are smaller than the chemical processes term in the northern hemisphere.…”

“…The residual term actually contains three terms that modify the ozone concentration: chemical production; molecular diffusion; and gravity waves (Ryan et al, ). Ryan et al () showed that the magnitudes of the gravity wave and molecular diffusion terms are smaller than the chemical processes term in the northern hemisphere. The residual term in equation may be an approximation of the net chemical production term.…”

“…waves (Ryan et al, 2018). Ryan et al (2018) showed that the magnitudes of the gravity wave and molecular diffusion terms are smaller than the chemical processes term in the northern hemisphere. The residual term in equation (4) may be an approximation of the net chemical production term.…”