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  • Author or Editor: D. W. Wang x
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D. Y. Wang
,
W. E. Ward
,
G. G. Shepherd
, and
Dongs-Liang Wu

Abstract

A climatology of stationary planetary waves (SPWs) in horizontal winds at latitudes 70°S–70°N and altitudes 90–120 km is obtained from Wind-Imaging Interferometer (WINDII) green line measurements in December–January and March–April of 1991–96. The observed solstitial SPW fields are relatively stronger and dominated by zonal wavenumber-1 variations. In contrast, the equinoctial SPW fields are weaker and characterized by zonal wavenumber-2 variations. The zonal amplitude maxima of 10–25 m s−1 are generally centered at the midlatitudes of 35°–40° in both hemispheres around 96 km, with the eastward perturbation velocity maxima around 90°E for wavenumber 1 and 60° and 240°E for wavenumber 2. The meridional amplitude maxima are about 5–15 m s−1 and show more variabilities in their latitude–height distributions. The meridional phases indicated that Eliassen–Palm (EP) fluxes were downward–poleward for the winter maxima, vertically varying poleward for the summer maxima, and more variable during March–April. The hemispheric–seasonal–interannual variations in amplitude and phase are of 10 m s−1 and 30°, respectively. In particular, a distinguishable local summer maximum with an amplitude of 10–20 m s−1 is found to exist in the wavenumber-1 variation of zonal wind component. The hemispheric asymmetry is also characterized by the nodal phase (or phase jump) lines shifted toward the winter hemisphere by 10°–30°. Wave penetrations across the equator are observed with amplitudes of 5 m s−1 at 97–100 km. While the summer maximum of the wavenumber-1 component persisted during the four years, large variability is found in the winter hemisphere where the wavenumber-2 component became significant at the 90–105-km region during December 1992–January 1993 and December 1993–January 1994 and at the 105–120-km region during December 1991–January 1992. The excitation due to in situ forcing of azonal gravity wave drag, which varies longitudinally, is thought to be largely responsible for the observed SPW, particularly for the summer maximum, while the leakage of upward propagating SPW from the lower to the higher atmosphere also plays a role, especially in the winter and the equinoctial periods.

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W. Feng
,
M. P. Chipperfield
,
H. K. Roscoe
,
J. J. Remedios
,
A. M. Waterfall
,
G. P. Stiller
,
N. Glatthor
,
M. Höpfner
, and
D.-Y. Wang

Abstract

An offline 3D chemical transport model (CTM) has been used to study the evolution of the Antarctic ozone hole during the sudden warming event of 2002 and to compare it with similar simulations for 2000. The CTM has a detailed stratospheric chemistry scheme and was forced by ECMWF and Met Office analyses. Both sets of meteorological analyses permit the CTM to produce a good simulation of the evolution of the 2002 vortex and its breakup, based on O3 comparisons with Total Ozone Mapping Spectrometer (TOMS) column data, sonde data, and first results from the Environmental Satellite–Michelson Interferometer for Passive Atmospheric Sounding (ENVISAT–MIPAS) instrument. The ozone chemical loss rates in the polar lower stratosphere in September 2002 were generally less than in 2000, because of the smaller average active chlorine, although around the time of the warming, the largest vortex chemical loss rates were similar to those in 2000 (i.e., −2.6 DU day−1 between 12 and 26 km). However, the disturbed vortex of 2002 caused a somewhat larger influence of polar processing on Southern Hemisphere (SH) midlatitudes in September. Overall, the calculations show that the average SH chemical O3 loss (poleward of 30°S) by September was ∼20 DU less in 2002 compared with 2000. A significant contribution to the much larger observed polar O3 column in September 2002 was due to the enhanced descent at the vortex edge and increased horizontal transport, associated with the distorted vortex.

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Xiang-Yu Li
,
Hailong Wang
,
Jingyi Chen
,
Satoshi Endo
,
Geet George
,
Brian Cairns
,
Seethala Chellappan
,
Xubin Zeng
,
Simon Kirschler
,
Christiane Voigt
,
Armin Sorooshian
,
Ewan Crosbie
,
Gao Chen
,
Richard Anthony Ferrare
,
William I. Gustafson Jr.
,
Johnathan W. Hair
,
Mary M. Kleb
,
Hongyu Liu
,
Richard Moore
,
David Painemal
,
Claire Robinson
,
Amy Jo Scarino
,
Michael Shook
,
Taylor J. Shingler
,
Kenneth Lee Thornhill
,
Florian Tornow
,
Heng Xiao
,
Luke D. Ziemba
, and
Paquita Zuidema

Abstract

Large-eddy simulation (LES) is able to capture key boundary layer (BL) turbulence and cloud processes. Yet, large-scale forcing and surface turbulent fluxes of sensible and latent heat are often poorly prescribed for LESs. We derive these quantities from measurements and reanalysis obtained for two cold-air outbreak (CAO) events during Phase I of the Aerosol Cloud Meteorology Interactions over the Western Atlantic Experiment (ACTIVATE) in February–March 2020. We study the two contrasting CAO cases by performing LES and test the sensitivity of BL structure and clouds to large-scale forcings and turbulent heat fluxes. Profiles of atmospheric state and large-scale divergence and surface turbulent heat fluxes obtained from ERA5 data agree reasonably well with those derived from ACTIVATE field measurements for both cases at the sampling time and location. Therefore, we adopt the time-evolving heat fluxes, wind, and advective tendencies profiles from ERA5 data to drive the LES. We find that large-scale thermodynamic advective tendencies and wind relaxations are important for the LES to capture the evolving observed BL meteorological states characterized by the hourly ERA5 data and validated by the observations. We show that the divergence (or vertical velocity) is important in regulating the BL growth driven by surface heat fluxes in LESs. The evolution of liquid water path is largely affected by the evolution of surface heat fluxes. The liquid water path simulated in LES agrees reasonably well with the ACTIVATE measurements. This study paves the path to investigate aerosol–cloud–meteorology interactions using LES informed and evaluated by ACTIVATE field measurements.

Full access
Xiang-Yu Li
,
Hailong Wang
,
Jingyi Chen
,
Satoshi Endo
,
Simon Kirschler
,
Christiane Voigt
,
Ewan Crosbie
,
Luke D. Ziemba
,
David Painemal
,
Brian Cairns
,
Johnathan W. Hair
,
Andrea F. Corral
,
Claire Robinson
,
Hossein Dadashazar
,
Armin Sorooshian
,
Gao Chen
,
Richard Anthony Ferrare
,
Mary M. Kleb
,
Hongyu Liu
,
Richard Moore
,
Amy Jo Scarino
,
Michael A. Shook
,
Taylor J. Shingler
,
Kenneth Lee Thornhill
,
Florian Tornow
,
Heng Xiao
, and
Xubin Zeng

Abstract

Aerosol effects on micro/macrophysical properties of marine stratocumulus clouds over the western North Atlantic Ocean (WNAO) are investigated using in situ measurements and large-eddy simulations (LES) for two cold-air outbreak (CAO) cases (28 February and 1 March 2020) during the Aerosol Cloud Meteorology Interactions over the Western Atlantic Experiment (ACTIVATE). The LES is able to reproduce the vertical profiles of liquid water content (LWC), effective radius r eff and cloud droplet number concentration Nc from fast cloud droplet probe (FCDP) in situ measurements for both cases. Furthermore, we show that aerosols affect cloud properties (Nc , r eff, and LWC) via the prescribed bulk hygroscopicity of aerosols ( κ ¯ ) and aerosol size distribution characteristics. Nc , r eff, and liquid water path (LWP) are positively correlated to κ ¯ and aerosol number concentration (Na ) while cloud fractional cover (CFC) is insensitive to κ ¯ and aerosol size distributions for the two cases. The realistic changes to aerosol size distribution (number concentration, width, and the geometrical diameter) with the same meteorology state allow us to investigate aerosol effects on cloud properties without meteorological feedback. We also use the LES results to evaluate cloud properties from two reanalysis products, ERA5 and MERRA-2. Compared to LES, the ERA5 is able to capture the time evolution of LWP and total cloud coverage within the study domain during both CAO cases while MERRA-2 underestimates them.

Open access