Midlatitude Atmosphere Research Articles

Evaluation of the Atmospheric Boundary-Layer Electrical Variability

Due to the chaotic motion of charged particles carried by turbulent eddies, electrical quantities in the atmospheric boundary layer (ABL) have short-term variability superimposed on long-term variability caused by sources from regional to global scales. In this study the influence of radon exhalation rate, aerosol distribution and turbulent transport efficiency on the variability of fair-weather atmospheric electricity is investigated via Lagrangian stochastic modelling. For the mid-latitude lower atmosphere undisturbed by precipitation, electrified clouds, or thunderstorms, the model is capable of reproducing the diurnal variation in atmospheric electrical parameters detected by ground-based measurements. Based on the analysis of field observations and numerical simulation it is found that the development of the convective boundary layer, accompanied by an increase in turbulent kinetic energy, forms the vertical distribution of radon and its decaying short-lived daughters to be approximately coincident with the barometric law for several eddy turnover times. In the daytime ABL the vertical distribution of atmospheric electrical conductivity tends to be uniform except within the surface layer, due to convective mixing of radon and its radioactive decay products. At the same time, a decrease in the conductivity near the ground is usually observed. This effect leads to an enhanced ground-level atmospheric electric field compared to that normally observed in the nocturnal stably-stratified boundary layer. The simulation showed that the variability of atmospheric electric field in the ABL associated with internal origins is significant in comparison to the variability related to changes in global parameters. It is suggested that vertical profiles of electrical quantities can serve as informative parameters on ABL turbulent dynamics and can even more broadly characterize the state of the environment.

Attribution of recent ozone changes in the Southern Hemisphere mid-latitudes using statistical analysis and chemistry–climate model simulations

Abstract. Ozone (O3) trends and variability from a 28-year (1987–2014) ozonesonde record at Lauder, New Zealand, have been analysed and interpreted using a statistical model and a global chemistry–climate model (CCM). Lauder is a clean rural measurement site often representative of the Southern Hemisphere (SH) mid-latitude background atmosphere. O3 trends over this period at this location are characterised by a significant positive trend below 6 km, a significant negative trend in the tropopause region and the lower stratosphere between 9 and 15 km, and no significant trend in the free troposphere (6–9 km) and the stratosphere above 15 km. We find that significant positive trends in lower tropospheric ozone are correlated with increasing temperature and decreasing relative humidity at the surface over this period, whereas significant negative trends in the upper troposphere and the lower stratosphere appear to be strongly linked to an upward trend of the tropopause height. Relative humidity and the tropopause height also dominate O3 variability at Lauder in the lower troposphere and the tropopause region, respectively. We perform an attribution of these trends to anthropogenic forcings including O3 precursors, greenhouse gases (GHGs), and O3-depleting substances (ODSs), using CCM simulations. Results indicate that changes in anthropogenic O3 precursors contribute significantly to stratospheric O3 reduction, changes in ODSs contribute significantly to tropospheric O3 reduction, and increased GHGs contribute significantly to stratospheric O3 increases at Lauder. Methane (CH4) likely contributes positively to O3 trends in both the troposphere and the stratosphere, but the contribution is not significant at the 95 % confidence level over this period. An extended analysis of CCM results covering 1960–2010 (i.e. starting well before the observations) reveals significant contributions from all forcings to O3 trends at Lauder – i.e. increases in GHGs and the increase in CH4 alone all contribute significantly to O3 increases, net increases in ODSs lead to O3 reduction, and increases in non-methane O3 precursors cause O3 increases in the troposphere and reductions in the stratosphere. This study suggests that a long-term ozonesonde record obtained at a SH mid-latitude background site (corroborated by a surface O3 record at a nearby SH mid-latitude site, Baring Head, which also shows a significant positive trend) is a useful indicator for detecting atmospheric composition and climate change associated with human activities.

Late Twenty-First-Century Changes in the Midlatitude Atmospheric Circulation in the CESM Large Ensemble

AbstractProjected changes in the midlatitude atmospheric circulation at the end of the twenty-first century are investigated using coupled ocean–atmosphere simulations from the Community Earth System Model Large Ensemble (CESM-LENS). Different metrics are used to describe the response of the midlatitude atmospheric dynamics in 40 ensemble members covering the 1920–2100 period. Contrasted responses are identified depending on the season and longitudinal sector that are considered. In winter, a slowdown of the zonal flow and an increase in waviness is found over North America, while the European sector exhibits a reinforced westerly flow and decreased waviness. Extreme temperature events in midlatitudes are more sensitive to thermodynamical than dynamical changes, and a general decrease in the intensity of wintertime cold spells is found. Analyses of individual ensemble members reveal a large spread in circulation changes due to internal variability. Causes for this spread are found to be tied to the Arctic amplification in the Pacific–North American sector and to the polar stratosphere in the North Atlantic. A competition mechanism is also discussed between the midlatitude response to polar versus tropical changes. While the upper-tropospheric tropical warming pushes the jet stream poleward, in winter, Arctic amplification and the weaker polar vortex exert an opposite effect. This competition results in a narrowing of the jet path in the midlatitudes, leading to decreased/unchanged waviness/blockings. This interpretation somewhat reconciles conflicting results between the hypothesized effect of Arctic amplification and projected changes in midlatitude flow characteristics. This study also illustrates that further understanding of regional processes is critical for anticipating changes in the midlatitude dynamics.

Satellite Assessments of Tropopause Dry Intrusions Correlated to Mid-Latitude Storms

Dry intrusion is an important mid-latitude atmosphere phenomenon within the upper troposphere and lower stratosphere. It is often found to be related to the cyclogenesis, rainstorm, as well as convection generation and precipitation enhancement. Since the atmosphere environment for any of these above-mentioned weather is terribly complicated, those preexisting popular schemes which takes no account of water vapor may not suitable for detecting the dry intrusion related to such weather events. With regard to the merits and demerits of the current preexisting schemes, a new scheme based on Fengyun-2E geo-stationary satellite data is presented in this study to detect the tropopause dry intrusion. The scheme is set up based on the statistical relationship between water vapor at high level troposphere, the general moist potential vorticity, ozone concentration and upper-level jets. Validations are made by using Fengyun-3B observed ozone profiles and NCEP FNL analysis data. Two mid-latitude storm episodes occurred in China in 2012 and 2014 are selected as demonstration to show the applicability of the method we developed in this study. Good application effects in both cases suggest that the new method for detecting dry intrusion is applicable and can be helpful in middle-latitude disastrous weather monitoring and forecasting.

Atmospheric eddy anomalies associated with the wintertime North Pacific subtropical front strength and their influences on the seasonal-mean atmosphere

This study investigates transient eddy activity anomalies in the mid-latitude upper troposphere associated with intensity variability of the wintertime North Pacific subtropical front. Our results show that the meridional gradient of air temperature and baroclinic instability in the mid-latitude atmosphere become stronger as the subtropical front intensifies, and the mid-latitude westerly jet accelerates with barotropic structure. We further divide the mid-latitude atmospheric eddy activities into high- (2–7 days) and low-frequency (10–90 days) eddy activities according to their life periods. We find that, when the oceanic subtropical front intensifies, the high-frequency atmospheric eddy activity in the mid-latitudes strengthens while the low-frequency eddy activity weakens. The stronger high-frequency eddy activity tends to moderate the air temperature gradient and baroclinicity in the mid-latitudes. High-frequency eddy anomalies accelerate the westerly jet on the northern side and downstream of the westerly jet, and enhance the jet with equivalent barotropic structure. In contrast, the weaker low-frequency eddy activity has a negative contribution to zonal wind speed tendency and attenuates the zonal homogenization of the jet. The anomalous thermodynamic forcing of the low-frequency eddy activity helps maintain the meridional gradient of air temperature in the mid-troposphere.

Barotropic kinetic energy and enstrophy transfers in the atmosphere

AbstractThe midlatitude atmosphere is characterized by turbulent eddies that act to produce a depth‐independent (barotropic) mean flow. Using the NCEP (National Centers for Environmental Prediction) Reanalysis 2 data, the latitudinal dependence of barotropic kinetic energy and enstrophy are investigated. Most of the barotropization takes place in the extratropics with a maximum value at midlatitudes, due to the latitudinal variations of the static stability, tropopause height, and sphericity of the planet. Barotropic advection transfers the eddy kinetic energy to the zonal mean flow and thus maintains the barotropic component of the eddy‐driven jet. The classic description of geostrophic turbulence exists only at high latitudes, where the quasi‐geostrophic flow is supercritical to baroclinic instability; the eddy‐eddy interactions carry both the barotropization of eddy kinetic energy upscale to the Rhines scale and the barotropization of eddy potential enstrophy downscale.

Equilibrium states of the Charney-DeVore quasi-geostrophic equation in mid-latitude atmosphere

On the predictability of atmospheric blocking in the mid-latitude atmosphere, a quasi-geostrophic beta-plane channel model equation was introduced in a pioneering work by Charney and DeVore in 1979 based on the understanding of quasi-stationary weather patterns. The equation is driven by a zonal thermal flow representing a mid-latitude westerly jet and a wave function representing an ocean land topography. They truncated the equation into a three spectral mode model, which gives rise to the existence of multiple equilibrium states showing a blocking mechanism profile. Moreover, they predicted numerically the absence of the multiple equilibrium states with respect to the flat topography situation. In the present paper, this absence observation is discussed from rigorous analysis and the coexistence of two stable equilibrium states, similarly to the three mode model equilibrium states accounting for atmospheric blocking, is investigated numerically with the increment of topographic amplitude.

Dynamical analysis of blocking events: spatial and temporal fluctuations of covariant Lyapunov vectors

One of the most relevant weather regimes in the midlatitude atmosphere is the persistent deviation from the approximately zonally symmetric jet stream leading to the emergence of so‐called blocking patterns. Such configurations are usually connected to exceptional local stability properties of the flow which come along with an improved local forecast skills during the phenomenon. It is instead extremely hard to predict onset and decay of blockings. Covariant Lyapunov Vectors (CLVs) offer a suitable characterization of the linear stability of a chaotic flow, since they represent the full tangent linear dynamics by a covariant basis which explores linear perturbations at all time scales. Therefore, we assess whether CLVs feature a signature of the blockings. As a first step, we examine the CLVs for a quasi‐geostrophic beta‐plane two‐layer model in a periodic channel baroclinically driven by a meridional temperature gradient ΔT. An orographic forcing enhances the emergence of localized blocked regimes. We detect the blocking events of the channel flow with a Tibaldi‐Molteni scheme adapted to the periodic channel. When blocking occurs, the global growth rates of the fastest growing CLVs are significantly higher. Hence, against intuition, the circulation is globally more unstable in blocked phases. Such an increase in the finite time Lyapunov exponents with respect to the long term average is attributed to stronger barotropic and baroclinic conversion in the case of high temperature gradients, while for low values of ΔT, the effect is only due to stronger barotropic instability. In order to determine the localization of the CLVs we compare the meridionally averaged variance of the CLVs during blocked and unblocked phases. We find that on average the variance of the CLVs is clustered around the center of blocking. These results show that the blocked flow affects all time scales and processes described by the CLVs.

On the Observed Relationships between Variability in Gulf Stream Sea Surface Temperatures and the Atmospheric Circulation over the North Atlantic

Abstract The advent of increasingly high-resolution satellite observations and numerical models has led to a series of advances in understanding the role of midlatitude sea surface temperature (SST) in climate variability, especially near western boundary currents (WBC). Observational analyses suggest that ocean dynamics play a central role in driving interannual SST variability over the Kuroshio–Oyashio and Gulf Stream extensions. Numerical experiments suggest that variations in the SST field within these WBC regions may have a much more pronounced influence on the atmospheric circulation than previously thought. In this study, the authors examine the observational support for (or against) a robust atmospheric response to midlatitude SST variability in the Gulf Stream extension. To do so, they apply lead–lag analysis based on daily mean data to assess the evidence for two-way coupling between SST anomalies and the atmospheric circulation on transient time scales, building off of previous studies that have utilized weekly data. A novel decomposition approach is employed to demonstrate that atmospheric circulation anomalies over the Gulf Stream extension can be separated into two distinct patterns of midlatitude atmosphere–ocean interaction: 1) a pattern that peaks 2–3 weeks before the largest SST anomalies in the Gulf Stream extension, which can be viewed as the “atmospheric forcing,” and 2) a pattern that peaks several weeks after the largest SST anomalies, which the authors argue can be viewed as the “atmospheric response.” The latter pattern is linearly independent of the former and is interpreted as the potential response of the atmospheric circulation to SST variability in the Gulf Stream extension.

Mid-latitude atmosphere and ionosphere connection as revealed by very low frequency signals

Quantitative information about the effect of atmospheric influences on the variability of upper mesosphere–lower ionosphere (UMLI) region is not clearly known yet. To investigate the relationship between the lower atmosphere and UMLI region, we compared the amplitude of very low frequency (VLF) signals with the atmospheric parameters such as total column Ozone (TCO) density and stratospheric temperature at various heights for the first time for three different latitudinal regions. We show that the VLF amplitude is strongly correlated with the TCO density, stratospheric temperatures for mid-latitude propagation paths throughout the years. For high and low latitude regions, this correlation between the VLF amplitude and atmospheric parameters is poor and not significant. This study indicates the experimental observation of latitudinal dependence of atmospheric influence on the upper mesosphere.

The role of variability in transport for large-scale flow dynamics

We develop a framework to study the role of variability in transport across a kinematically-defined boundary defined as a streamline in a reference flow. Two complementary schemes are presented: a graphical approach appropriate for analyzing specific cases of variability, and an analytical approach for analyzing the effect of general fluid properties on variability. Spatio-temporal nonlinear interaction between dynamic variability and the reference flow leads to flux variability that governs the transport processes. A characteristic length-scale of dynamic and flux variability can be expressed with the units of time using the flight time of the trajectory along the kinematically defined boundary. The characteristic time-scale of the flux variability is that of dynamic variability with the units of time. The non-dimensional ratio of the two characteristic scales is shown to be a critical parameter for evaluating the effectiveness of variability on transport. The pseudo-lobe sequence along the reference streamline describes spatial coherency of transport. The emergence of the pseudo-lobe sequence is likely to be synchronous with the flux variability. Once a pseudo-lobe sequence is formed, the characteristic length-scale of the flux variability regulates the width of the pseudo-lobes. In contrast, for transport over a fixed time interval and spatial segment, the characteristic time-scale of the dynamic variability regulates the width of the pseudo-lobes. Using a kinematic model, we demonstrate the framework for two types of transports in a blocked flow of the mid-latitude atmosphere: across the meandering jet axis and between the jet and recirculation cell.

Finite-volume models with implicit subgrid-scale parameterization for the differentially heated rotating annulus

The differentially heated rotating annulus is a classical experiment for the investigation of baroclinic flows and can be regarded as a strongly simplified laboratory model of the atmosphere in mid-latitudes. Data of this experiment, measured at the BTU Cottbus-Senftenberg, are used to validate two numerical finite-volume models (INCA and cylFloit) which differ basically in their grid structure. Both models employ an implicit parameterization of the subgrid-scale turbulence by the Adaptive Local Deconvolution Method (ALDM). One part of the laboratory procedure, which is commonly neglected in simulations, is the annulus spin-up. During this phase the annulus is accelerated from a state of rest to a desired angular velocity. We use a simple modelling approach of the spin-up to investigate whether it increases the agreement between experiment and simulation. The model validation compares the azimuthal mode numbers of the baroclinic waves and does a principal component analysis of time series of the temperature field. The Eady model of baroclinic instability provides a guideline for the qualitative understanding of the observations.

Correction of ozone influence on TOA radiance

An accurate atmospheric correction (AC) of Earth remote-sensing data in the spectral region 450–800 nm has to account for the ozone gas absorption influence. Usual operational AC codes employ a fixed ozone concentration corresponding to a climatologic average for a certain region and season, e.g. the mid-latitude summer atmosphere of the Moderate Resolution Atmospheric Transmission (MODTRAN) code. The reasons for a fixed ozone column are that ozone does not vary rapidly on a spatial and temporal scale, and additionally, the look-up table (LUT) size for AC is already big. This means that another degree of freedom for the ozone parameter would dramatically increase the size of the LUT database and the time required for LUT interpolation. In order to account for this effect, we use already existing LUTs that were calculated for a certain ozone reference level, e.g. an ozone column of g = 330 Dobson Units (DU) for MODTRAN’s mid-latitude summer atmosphere. Then the deviation of the top-of-atmosphere (TOA) radiance ΔL(g) from the reference level L(g = 330) is calculated as a function of solar and view geometries. The calculation is performed for a set of 36 wavelengths in the ozone-sensitive spectrum (450–800 nm) and five ozone columns. The last step computes the linear regression coefficients for each wavelength and geometry. The results are stored in a small table (11 kB). It is shown that the ozone influence is accurately accounted for by multiplying the modelled radiance L(g = 330) with a factor depending on g and wavelength yielding TOA radiance relative errors smaller than 0.5% for a wide range of ozone concentrations between 180 and 500 DU. Selected examples of a sensitivity study of the ozone effect on the retrieval of water constituents demonstrate the need to account for ozone in the AC step.

Land Surface Temperature Retrieval from the Medium Resolution Spectral Imager (MERSI) Thermal Data

A single channel land surface temperature (LST) retrieval algorithm named Single Channel Water Vapor Dependent (SCWVD) method was presented for Medium Resolution Spectral Imager (MERSI) thermal infrared band aboard FengYun-3A (FY-3A) satellite. Water Vapor Content (WVC) is the only input parameter in the algorithm assuming the surface emissivity is known. NCEP reanalysis monthly mean datasets are used to develop the SCWVD algorithm. Some tests, including global numerical simulations and validations with both in-situ measurements and MODIS LST product at Lake Tahoe, USA, were carried out to evaluate the algorithm performance. Compared with NCEP data and U.S. standard mid-latitude summer atmosphere model, the retrieved LST from simulated MERSI brightness temperature with MODTRAN had a RMSE about 0.8 K. In the validation, MERSI Level 2 water vapor product was employed, and the MERSI band emissivity was evaluated using the MODIS band 31 and 32 emissivity with an empirical expression. The results show that the difference between the retrieved MERSI LST and the in-situ measurements is less than 1 K in most situations. The comparison with the MODIS LST products (V5) shows that the RMSE is about 2.3 K.

A Contrast in Precipitation Characteristics across the Baiu Front near Japan. Part I: TRMM PR Observation

Abstract Contrasts in precipitation characteristics across the baiu front are examined with Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data near Japan during June–July (1998–2011). The vertical structure of atmospheric stratification differs between the tropics and midlatitudes. On an average, the baiu front is found around the latitude that roughly divides the midlatitude atmosphere from the tropical atmosphere. Precipitation characteristics are compared between the southern and northern sides of the reference latitude of the baiu front, which is detected with equivalent potential temperature at 1000 hPa of 345 K in terms of the boundary between the tropics and midlatitudes. The results show that there are obvious differences in precipitation characteristics between the southern and northern sides. In the south, convective rainfall ratios (CRRs) are 40%–60%, which are larger than those in the north (20%–40%). Greater rainfall intensity and taller/deeper precipitation are also observed in the south. Moreover, the characteristics of precipitation features (PFs), which are contiguous areas of nonzero rainfall, differ between the southern and northern sides. In the north, wide stratiform precipitation systems with CRRs of 0%–40% and heights of 8–11 km are dominant. In the south, organized precipitation systems with heights of 12–14 km and CRRs of 30%–50% and those with very large heights (14–17 km) and CRRs of 50%–80% are dominant in addition to wide stratiform precipitation systems. These results suggest that the mechanisms to bring rainfall are different between the southern and northern regions of the baiu front.

Stratospheric sudden warming effects on winds and temperature in the middle atmosphere at middle and low latitudes: a study using WACCM

Abstract. A stratospheric sudden warming (SSW) is a dynamical phenomenon of the wintertime stratosphere caused by the interaction between planetary Rossby waves propagating from the troposphere and the stratospheric zonal-mean flow. While the effects of SSW events are seen predominantly in high latitudes, they can also produce significant changes in middle and low latitude temperature and winds. In this study we quantify the middle and low latitude effects of SSW events on temperature and zonal-mean winds using a composite of SSW events between 1988 and 2010 simulated with the specified dynamics version of the Whole Atmosphere Community Climate Model (WACCM). The temperature and wind responses seen in the tropics also extend into the low latitudes in the other hemisphere. There is variability in observed zonal-mean winds and temperature depending on the observing location within the displaced or split polar vortex and propagation direction of the planetary waves. The propagation of planetary waves show that they originate in mid–high latitudes and propagate upward and equatorward into the mid-latitude middle atmosphere where they produce westward forcing reaching peak values of ~ 60–70 m s−1 day−1. These propagation paths in the lower latitude stratosphere appear to depend on the phase of the quasi-biennial oscillation (QBO). During the easterly phase of the QBO, waves originating at high latitudes propagate across the equator, while in the westerly phase of the QBO, the planetary waves break at ~ 20–25° N and there is no propagation across the equator. The propagation of planetary waves across the equator during the easterly phase of the QBO reduces the tropical upwelling and poleward flow in the upper stratosphere.

Vertical propagation of planetary-scale waves in variable background winds in the upper cloud region of Venus

Recently it was found that the low-latitude zonal wind and the amplitudes of Kelvin and Rossby waves at the cloud top of Venus show long-term variations in a synchronized manner. For the purpose of explaining this synchronization, we investigated the influence of the background zonal wind profile on the upward propagation of Kelvin and Rossby waves at altitudes 60–80km. Results from a linearized primitive equation model suggests that Kelvin waves can reach the cloud top height when the background wind speed is slow, whereas Rossby waves can reach the cloud top when the background wind speed is fast. These features obtained from the model are consistent with the observations. Since the momentum deposition by these waves can accelerate or decelerate the mean flow, these waves may contribute to the variation of the background wind. The calculated spatial distributions of the momentum dissipation indicate that the Kelvin waves accelerate the low-latitude atmosphere, and thus they can act to induce transition from the slow wind period to the fast wind period. On the other hand, the Rossby waves decelerate mainly the mid-latitude atmosphere, so that additional mechanisms are required to decelerate the low-latitude atmosphere. A possible mechanism is momentum advection caused by the Rossby wave-induced meridional circulation.

Dynamics of Undisturbed Midlatitude Atmospheric Electricity: From Observations to Scaling

Long-term dynamics of the electric field of the midlatitude near-surface atmosphere in a wide range of temporal scales is analyzed according to multiyear observatory and seasonal field observations. It is found that the daily dynamics of the aeroelectric field at mid-latitudes most authentically repeats a diurnal variation for the winter months. It is stated that short-period pulsations of the electric field have a self-similar power-law spectrum. Spatio-temporal scales of the self-similarity interval are estimated and the nature of the generalized diffusive process of the aeroelectric pulsation generation is defined. Characteristics of the turbulent ΔE pulsations are analyzed. Estimates of interrelation between the dynamic (fractal dimensions, intermittency indices) and power (degrees of spectral index and structure function) ΔE characteristics are obtained. Mutual correlations between atmospheric electric field variations, vertical atmospheric electrical current density, space charge density, and atmospheric electrical conductivity are studied. It is shown that variations of the light atmospheric ion number density and space charge density are related with variations of the Radon-222 emanations. Spectral analysis of the space charge density variations is carried out. It is shown that the electrodynamic state of the surface atmosphere depends on the convective state of the atmospheric boundary layer.

Modeled interaction between the subseasonal evolving of the East Asian summer monsoon and the direct effect of anthropogenic sulfate

AbstractA regional climate model is used to conduct four experiments to reveal the interaction between the subseasonal evolving of the East Asia summer monsoon (EASM) and the direct effect of anthropogenic sulfate. One of the experiments is conducted without the emission of anthropogenic SO2. The other three are carried out with the 1, 1.5, and 2 multiples of the SO2 emission of 2000, respectively. The model results suggest that in the rainfall, wind, and circulation of the EASM, the changes caused by the direct effect of anthropogenic sulfate on subseasonal time scale are within the model variability. The change of the EASM rainfall is not sensitive to sulfate forcing on subseasonal time scale but sensitive to the forcing on seasonal time scale. Moreover, rainfall change in the forcing experiments is significantly less (greater) than zero to the south (north) of the EASM rainfall centers on subseasonal time scale, but the EASM rainfall phase is not changed. The rainfall change associates with the correspondingly significant increase (decrease) of the atmospheric stability induced by the forcing of sulfate direct effect. The direct effect of sulfate plays different roles in different stages of the EASM subseasonal evolving. In the early stage, the EASM is significantly enhanced in terms of the interaction between tropical and midlatitude atmosphere. In the late stage, the EASM is weakened in terms of the large‐scale atmospheric circulation. Lastly, the responses of the rainfall, wind, and circulation of the EASM to the linear changes in the SO2 emission are nonlinear.

The effect of aerosols on long wave radiation and global warming

The effect of aerosols on long wave (LW) radiation was studied based on narrowband LW calculations in a reference mid-latitude summer atmosphere with and without aerosols. Aerosols were added to the narrowband LW scheme based on their typical schematic observed spectral and vertical behaviour over European land areas. This was found to agree also with the spectral aerosol data from the Lan Zhou University Semi-Arid Climate Observatory and Laboratory measurement stations in the north-western China.A volcanic stratospheric aerosol load was found to induce local LW warming and a stronger column “greenhouse effect” than a doubled CO2 concentration. A heavy near-surface aerosol load was found to increase the downwelling LW radiation to the surface and to reduce the outgoing LW radiation, acting very much like a thin low cloud in increasing the LW greenhouse effect of the atmosphere. The short wave reflection of white aerosol has, however, stronger impact in general, but the aerosol LW greenhouse effect is non-negligible under heavy aerosol loads.