Kazuyuki Miyazaki

Eliassen–Palm Flux Diagnosis Based on Isentropic Representation

Abstract This paper demonstrates an isentropic representation of the Eliassen–Palm flux (EP flux) as a tool for diagnosis of the atmospheric zonal mean states. This is a full extension of the transformed Eulerian mean (TEM) to express lower boundary conditions and finite-amplitude effects of waves. The isentropic EP flux is diagnosed from the NCEP–NCAR reanalysis for 12 yr and compared with the TEM. In the free atmosphere, the two diagnoses show similarities in the mass streamfunction and in the EP flux except that the EP flux divergence is somewhat different near the polar vortex. The similarities reflect the equivalency between the two schemes under the quasigeostrophic assumptions. However, the lower boundary values are very different between the two schemes. In the TEM, the vertical EP flux inaccurately suggests a much larger momentum flux coming out from the surface. In the isentropic diagnosis, the lower boundary value of vertical EP flux, which expresses the momentum exchange with the earths surfa...

Transport and Mixing in the Extratropical Tropopause Region in a High-Vertical-Resolution GCM. Part II: Relative Importance of Large-Scale and Small-Scale Dynamics

Abstract The relative roles of atmospheric motions on various scales, from mesoscale to planetary scale, in transport and mixing in the extratropical tropopause region are investigated using a high-vertical-resolution general circulation model (GCM). The GCM with a vertical resolution of about 300 m explicitly represents the propagation and breaking of gravity waves and the induced transport and mixing. A downward control calculation shows that the Eliassen–Palm (E-P) flux of the gravity waves diverges and induces a mean equatorward flow in the extratropical tropopause region, which differs from the mean poleward flow induced by the convergence of large-scale E-P fluxes. The diffusion coefficients estimated from the eddy potential vorticity flux in tropopause-based coordinates reveal that isentropic motions diffuse air between 20 K below and 10 K above the tropopause from late autumn to early spring, while vertical mixing is strongly suppressed at around 10–15 K above the tropopause throughout the year. T...

The Gradient Genesis of Stratospheric Trace Species in the Subtropics and around the Polar Vortex

Abstract Mechanisms that control the formation and decay of meridional gradients in stratospheric trace species in the subtropics and around the polar vortex are investigated using a gradient genesis equation that uses mass-weighted isentropic zonal means. Application of this method to global nitrous oxide (N2O) data output from a global chemical transport model shows that mean vertical transport increases the meridional tracer gradient from the subtropics to midlatitudes through the shearing deformation, particularly related to overturning of the Brewer–Dobson circulation. Mean meridional transport advects the subtropical tracer gradient toward midlatitudes, while the eddy stairstep effect, steepening at the edge of the well-mixed region because of a meridional gradient in the diffusion coefficient, increases the tracer gradient in the subtropics and around the polar vortex. Mechanisms controlling the evolution of the tracer gradients in the subtropics differ between spring and autumn. The autumnal subtr...

On the Analysis of Mean Downward Velocities around the Antarctic Polar Vortex

Abstract The Lagrangian characteristics of vertical motions around the Antarctic polar vortex are investigated using a general circulation model (GCM) and various analysis methods. A trace analysis that estimated the vertical velocity from the vertical displacement of tracer isopleths confirmed that using zonal means at geographical latitudes gives a Lagrangian mean circulation around the Antarctic polar vortex similar to that computed using equivalent latitudes. In the mass-weighted isentropic zonal means, the mean vertical velocity dynamically estimated from the meridional velocity shows strong downward motion outside the Antarctic polar vortex around 45°–55°S in the lower stratosphere, which is consistent with the thermodynamically estimated values from the diabatic heating rate. In comparison, the transformed Eulerian mean analysis tends to overestimate the downward velocity outside the Antarctic polar vortex and underestimate it inside the Antarctic polar vortex. Trace analysis produces a good approx...

Unexpected slowdown of US pollutant emission reduction in the past decade

Significance Emissions of nitrogen oxides (NOx) have a large impact on air quality and climate change as precursors in the formation of ozone and secondary aerosols. We find that NOx emissions have not been decreasing as expected in recent years (2011–2015) when comparing top-down estimates from satellites and surface NO2 measurements to the trends predicted from the US Environmental Protection Agency’s emission inventory data. The discrepancy can be explained by the growing relative contribution of industrial, area, and off-road mobile sources of emissions, decreasing relative contribution of on-road gasoline vehicles, and slower than expected decreases in on-road diesel NOx emissions, with implications for air-quality management. Ground and satellite observations show that air pollution regulations in the United States (US) have resulted in substantial reductions in emissions and corresponding improvements in air quality over the last several decades. However, large uncertainties remain in evaluating how recent regulations affect different emission sectors and pollutant trends. Here we show a significant slowdown in decreasing US emissions of nitrogen oxides (NOx) and carbon monoxide (CO) for 2011–2015 using satellite and surface measurements. This observed slowdown in emission reductions is significantly different from the trend expected using US Environmental Protection Agency (EPA) bottom-up inventories and impedes compliance with local and federal agency air-quality goals. We find that the difference between observations and EPA’s NOx emission estimates could be explained by: (i) growing relative contributions of industrial, area, and off-road sources, (ii) decreasing relative contributions of on-road gasoline, and (iii) slower than expected decreases in on-road diesel emissions.

Retrievals of Tropospheric Ozone Profiles from the SynergicObservation of AIRS and OMI: Methodology and Validation

The Tropospheric Emission Spectrometer (TES) on the A-Train Aura satellite was designed to profile tropospheric ozone and its precursors, taking measurements from 2004 to 2018. Starting in 2008, TES global sampling of tropospheric 15 ozone was gradually reduced in latitude with global coverage stopping in 2011. To extend the record of TES, this work presents a multispectral approach that will provide O3 data products with vertical resolution and measurement uncertainty similar to TES by combining the single-footprint thermal infrared (TIR) hyperspectral radiances from the Aqua Atmospheric Infrared Sounder (AIRS) instrument and the ultraviolet (UV) channels from the Aura Ozone Monitoring Instrument (OMI). The joint AIR+OMI O3 retrievals are processed through the MUlti-SpEctra, MUlti-SpEcies, MUlti-SEnsors (MUSES) retrieval 20 algorithm. Comparisons of collocated joint AIRS+OMI and TES to ozonesonde measurements show that both systems have similar errors, with mean and standard deviation of the differences well within the estimated measurement uncertainty. AIRS+OMI and TES have slightly different biases (within 5 parts per billion) versus the sondes. Both AIRS and OMI have wide swath widths (~1,650 km for AIRS; ~2,600 km for OMI) across satellite ground tracks. Consequently, the joint AIRS+OMI measurements have the potential to maintain TES vertical sensitivity while increasing coverage by two orders of 25 magnitude, thus providing an unprecedented new dataset to quantify the evolution of tropospheric ozone. Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2018-138 Manuscript under review for journal Atmos. Meas. Tech. Discussion started: 16 May 2018 c