Variations in Ozone Concentration over the Mid-Latitude Region Revealed by Ozonesonde Observations in Pohang, South Korea

Ozone absorbs harmful UV rays at high elevations but acts as a pollutant gas in the lower atmosphere. It is necessary to monitor both the vertical profile and the total column ozone. In this study, variations in the ozone concentration of Pohang were divided into three vertical layers: the stratospheric layer (STL), the second ozone peak layer (SOPL), and the tropospheric layer (TRL). Our results indicated that the ozone concentration in the STL, SOPL, TRL, and total column ozone increased by 0.45%, 2.64%, 5.26%, and 1.07% decade−1, respectively. The increase in the SOPL during springtime indicates that stratosphere–troposphere exchange is accelerating, while the increase during summertime appears to have been influenced by the lower layers. The growth of tropospheric ozone concentration is the result of both increased ozone precursors from industrialization in East Asia and the influx of stratospheric ozone. Our results reaffirmed the trend of ozone concentration in mid-latitudes of the northern hemisphere from vertical profiles in Pohang and, in particular, suggests that the recent changes of ozone in this region need to be carefully monitored.

Depolarization and lidar ratios at 355, 532, and 1064 nm and microphysical properties of aged tropospheric and stratospheric Canadian wildfire smoke

We present spectrally resolved optical and microphysical properties of western Canadian wildfire smoke observed in a tropospheric layer from 5–6.5 km height and in a stratospheric layer from 15–16 km height during a record-breaking smoke event on 22 August 2017. Three polarization/Raman lidars were run at the European Aerosol Research Lidar Network (EARLINET) station of Leipzig, Germany, after sunset on 22 August. For the first time, the linear depolarization ratio and extinction-to-backscatter ratio (lidar ratio) of aged smoke particles were measured at all three important lidar wavelengths of 355, 532, and 1064 nm. Very different particle depolarization ratios were found in the troposphere and in the stratosphere. The obviously compact and spherical tropospheric smoke particles caused almost no depolarization of backscattered laser radiation at all three wavelengths (<3 %), whereas the dry irregularly shaped soot particles in the stratosphere lead to high depolarization ratios of 22 % at 355 nm and 18 % at 532 nm and a comparably low value of 4 % at 1064 nm. The lidar ratios were 40–45 sr (355 nm), 65–80 sr (532 nm), and 80–95 sr (1064 nm) in both the tropospheric and stratospheric smoke layers indicating similar scattering and absorption properties. The strong wavelength dependence of the stratospheric depolarization ratio was probably caused by the absence of a particle coarse mode (particle mode consisting of particles with radius >500 nm). The stratospheric smoke particles formed a pronounced accumulation mode (in terms of particle volume or mass) centered at a particle radius of 350–400 nm. The effective particle radius was 0.32 µm. The tropospheric smoke particles were much smaller (effective radius of 0.17 µm). Mass concentrations were of the order of 5.5 µg m−3 (tropospheric layer) and 40 µg m−3 (stratospheric layer) in the night of 22 August 2017. The single scattering albedo of the stratospheric particles was estimated to be 0.74, 0.8, and 0.83 at 355, 532, and 1064 nm, respectively.

Extreme levels of Canadian wildfire smoke in the stratosphere over central Europe – Part 2: Lidar study of depolarization and lidar ratios at 355, 532, and 1064 nm and of microphysical properties

Extremely high particle extinction coefficients, an order of magnitude higher than after the Mt. Pinatubo eruption in 1991, were measured in the stratosphere over Leipzig, Germany, on 22 August 2017. In a series of two articles, we present our observations of this record-breaking smoke event. In part 1 (Ansmann et al., 2018), we provide an overview of the smoke situation. The particle extinction coefficients reached 500 Mm−1 at 532 nm in the lower stratosphere around 15 km height and the smoke-related aerosol optical thickness (AOT) was close to 1.0 around noon. In part 2, we present the optical and microphysical properties of the fire smoke observed in a tropospheric layer from 5–6.5 km height and in a stratospheric layer from 15–16 km height. Three Raman lidars were run at Leipzig after sunset on 22 August. As a highlight, triple-wavelength polarization/Raman lidar measurements of the particle depolarization ratio and extinction-to-backscatter ratio (lidar ratio) at all three important lidar wavelengths of 355, 532, and 1064 nm could be performed. Very different particle depolarization ratios were found in the troposphere and in the stratosphere. The obviously compact and spherical tropospheric smoke particles caused almost no depolarization of backscattered laser radiation at all three wavelength (

ANÁLISIS SINÓPTICO DE UN EVENTO EXTREMO Y PERSISTENTE DE LLUVIA SOBRE EL ESTADO DE RÍO GRANDE DO SUL, BRASIL, EN MAYO DE 2004

Between 04 to 09 May 2004, part of the state of Rio Grande do Sul (RS), Brazil; have recorded rainfall above 300mm. The east region of this state, mainly on the coast, had the highest rainfall accumulation occurred. A synoptic analysis of this period has shown a persistent trough west of RS in high and middle levels of troposphere, in the first three days of this event. This trough started a cyclonic vortice in the mid-low-tropospheric levels in the following days. The upward movement associated with this trough stayed semi-stationary over the state of RS and acted in almost entire tropospheric layer during great part of this period. In addition, it was observed that this tropospheric layer had high values of relative humidity from surface up to 300 hPa, over the state of RS – greater than 70%. In 09 May 2004, the cyclonic vortice has lost their configuration and has distanced from RS. The state of RS was dominated by an anticyclonic circulation and by a drier tropospheric layer, what disfavors rainfall occurrence in this region. During all analyzed period, it could be observed that the configuration in the middle troposphere has extended up to higher levels, but the same does not occurred to the surface. Also, a cyclonic circulation in 850 hPa was observed over the state of RS, but any cyclogenesis has occurred at surface. A surface cyclogenesis was observed over the coast of the state of Sao Paulo (SP), in 05 May. This cyclone has moved to south, approaching the coast of the states of RS e Santa Catarina (SC), in 08 May. A comparison of the atmospheric behavior with the rainfall recorded in the state of RS between 03 and 09 May suggest that this low-pressure center has no direct influence in the cumulative rainfall observed in this period. In addition, in 08 and 09 May, this low-pressure center weakened and move away from the coast of the states of RS and SC. Therefore, although the weak low-level temperature advection and low-level moisture flux convergence observed over this region, a persistent mid-low-tropospheric trough, what favor persistent upward movement, together with a deep and very humid layer, seems to be the main responsible to the great amounts of rainfall registered in the state of RS.

Improved retrieval of direct and diffuse downwelling surface shortwave flux in cloudless atmosphere using dynamic estimates of aerosol content and type: application to the LSA-SAF project

Downwelling surface shortwave flux (DSSF) is a key parameter to addressing many climate, meteorological, and solar energy issues. Under clear sky conditions, DSSF is particularly sensitive to the variability both in time and space of the aerosol load and chemical composition. Hitherto, this dependence has not been properly addressed by the Satellite Application Facility on Land Surface Analysis (LSA-SAF), which operationally disseminates instantaneous DSSF products over the continents since 2005 considering constant aerosol conditions. In the present study, an efficient method is proposed for DSSF retrieval that will overcome the limitations of the current LSA-SAF product. This method referred to as SIRAMix (Surface Incident Radiation estimation using Aerosol Mixtures) is based upon an accurate physical parameterization coupled with a radiative transfer-based look up table of aerosol properties. SIRAMix considers a tropospheric layer composed of several major aerosol species that are conveniently mixed to reproduce real aerosol conditions as best as possible. This feature of SIRAMix allows it to provide not only accurate estimates of global DSSF but also the direct and diffuse DSSF components, which are crucial radiative terms in many climatological applications. The implementation of SIRAMix is tested in the present article using atmospheric analyses from the European Center for Medium-Range Weather Forecasts (ECMWF). DSSF estimates provided by SIRAMix are compared against instantaneous DSSF measurements taken at several ground stations belonging to several radiation measurement networks. Results show an average root mean square error (RMSE) of 23.6, 59.1, and 44.9 W m−2 for global, direct, and diffuse DSSF, respectively. These scores decrease the average RMSE obtained for the current LSA-SAF product by 18.6%, which only provides global DSSF for the time being, and, to a lesser extent, for the state of the art in the matter of DSSF retrieval (RMSE decrease of 10.9, 6.5, and 19.1% for global, direct, and diffuse DSSF with regard to the McClear algorithm). The main limitation of the proposed approach is its high sensitivity to the quality of the ECMWF aerosol inputs, which is proved to be sufficiently accurate for reanalyses but not for forecast data. Given the proximity of DSSF retrieval to the modeling of the atmospheric direct effect, SIRAMix is also able to quantify the direct radiative forcing at the surface due to a given atmospheric component (e.g., gases or aerosols).

Tropopause Structure and the Role of Eddies

This paper presents a series of dynamical states using an idealized three-dimensional general circulation model with gray radiation and latent heat release. Beginning with the case of radiative–convective equilibrium, an eddy-free two-dimensional state with zonally symmetric flow is developed, followed by a three-dimensional state that includes baroclinic eddy fluxes. In both dry and moist cases, it is found that the deepening of the tropical tropospheric layer and the shape of the extratropical tropopause can be understood through eddy-driven processes such as the stratospheric Brewer–Dobson circulation. These results suggest that eddies alone can generate a realistic tropopause profile in the absence of moist convection and that stratospheric circulation is an important contributor to tropopause structure.

Abrupt Transition to Strong Superrotation in an Axisymmetric Model of the Upper Troposphere

Abrupt transitions to strongly superrotating states have been found in some idealized models of the troposphere. These transitions are thought to be caused by feedbacks between the eddy momentum flux convergence in low latitudes and the strength of the equatorial flow. The behavior of an axisymmetric shallow-water model with an applied tropical torque is studied here to determine if an abrupt transition can be realized without eddy feedbacks. The upper-tropospheric layer is relaxed to a radiative equilibrium thickness, exchanging mass and thus momentum with the nonmoving lower layer. For low values of the applied torque, the circulation is earthlike; however, for larger values, an abrupt transition to a strongly superrotating state can occur. In some cases, the system remains superrotating as the torque is subsequently decreased. A simple analytical model is used to better understand the system. The bifurcation is caused by a feedback between the applied torque and the strength of the Hadley cell. As the torque increases, the strength of the cell decreases, reducing the damping caused by momentum transfer from the lower layer.