ALBERT

Description: In this paper, the field experiments on ground surface spectral broadband solar radiation (SR) and corresponding albedo were introduced at three man-made sites at Gobi, desert and bare loess zones during three different intensive observational periods (IOP) from 2010 to 2013 in Gansu Province, respectively. The continuous and high temporal resolution records of ground surface solar radiation are presented, including global (GR), ultraviolet (UV), visible (VIS), and near-infrared radiation (NIR). The corresponding albedos are analyzed over three typical non-vegetated underlying surfaces in arid and semi-arid and semi-humid regions of northwestern China. The preliminary investigations were carried out. The results show: the variation trends of UV, VIS and NIR are coincident with the GR, and the irradiances are gradually decreasing throughout the IOP at each site; the energy ratios of VIS/GR are all approximately 40.2%, and the ratios of NIR/GR are all approximately 54.4% at the Gobi, desert and bare loess zones; the averaged albedos of the soil for VIS are 0.231, 0.211 and 0.142, for the NIR are 0.266, 0.252 and 0.255 over the Gobi, desert and bare loess land surfaces, respectively. The energy ratios of VIS/GR and NIR/GR are not 50% as prescribed for all of the soil color classes in most of land surface models (LSMs). The observational soil albedo values for NIR are not twice to that of the VIS as predicted in some LSMs for the underlying surface at the three sites. GR albedo is determined by the energy ratios of SR/GR and SR albedos.

Description: An analysis of the recently reconstructed gridded May-September total precipitation in the Indian monsoon region for the past half millennium discloses significant variations at multidecadal timescales. Meanwhile, paleo-climate modeling outputs from NCAR CCSM4 show similar multidecadal variations in the monsoon precipitation. One of those variations at the frequency of 40–50 years per cycle is examined in this study. Major results show that this variation is a product of the processes in that the meridional gradient of the atmospheric enthalpy is strengthened by radiation loss in the high-latitude and polar region. Driven by this gradient and associated baroclinicity in the atmosphere, more heat/energy is generated in the tropical and subtropical (monsoon) region and transported poleward. This transport relaxes the meridional enthalpy gradient and, subsequently, the need for heat production in the monsoon region. The multidecadal timescale of these processes results from atmospheric circulation-radiation interactions and the inefficiency in generation of kinetic energy from the potential energy in the atmosphere to drive the eddies that transport heat poleward. This inefficiency creates a time delay between the meridional gradient of the enthalpy and the poleward transport. The monsoon precipitation variation lags that in the meridional gradient of enthalpy but leads that of the poleward heat transport. This phase relationship, and underlining chasing process by the transport of heat to the need for it driven by the meridional enthalpy gradient, sustains this multidecadal variation. This mechanism suggests that atmospheric circulation processes can contribute to multidecadal timescale variations. Interactions of these processes with other forcing, such as SST or solar irradiance anomalies, can result in resonant or suppressed variations in the Indian monsoon precipitation.

Description: The impact on the dynamics of the stratosphere of three approaches to geoengineering by Solar Radiation Management is investigated using idealized simulations of a global climate model. The approaches are geoengineering with sulfate aerosols, titania aerosols and reduction in total solar irradiance (representing mirrors placed in space). If it were possible to use stratospheric aerosols to counterbalance the surface warming produced by a quadrupling of atmospheric carbon dioxide concentrations, tropical lower stratospheric radiative heating would drive a thermal-wind response which would intensify the stratospheric polar vortices. In the Northern Hemisphere this intensification results in strong dynamical cooling of the polar stratosphere. Northern Hemisphere stratospheric sudden warming events become rare (1 or 2 in 65 years for sulfate and titania respectively). The intensification of the polar vortices results in a poleward shift of the tropospheric midlatitude jets in winter. The aerosol radiative heating enhances the tropical upwelling in the lower stratosphere, influencing the strength of the Brewer-Dobson Circulation. In contrast, solar dimming does not produce heating of the tropical lower stratosphere so there is little intensification of the polar vortex and no enhanced tropical upwelling. The dynamical response to titania aerosol is qualitatively similar to the response to sulfate.

Description: Upper tropospheric and lower stratospheric (UTLS) measurements from the Aura Microwave Limb Sounder (MLS), the Aura High Resolution Dynamics Limb Sounder (HIRDLS), and the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) are used to present the first global climatological comparison of extratropical, non-polar trace gas distributions in double tropopause (DT) and single tropopause (ST) regions. Stratospheric tracers, O 3 , HNO 3 and HCl, have lower mixing ratios ~2–8 km above the primary (lowermost) tropopause in DT than in ST regions in all seasons, with maximum Northern Hemisphere (NH) differences near 50% in winter and 30% in summer. Southern Hemisphere (SH) winter differences are somewhat smaller, but summer differences are similar in the two hemispheres. H 2 O in DT regions of both hemispheres shows strong negative anomalies in November through February and positive anomalies in July through October, reflecting the strong seasonal cycle in H 2 O near the tropical tropopause. CO and other tropospheric tracers examined have higher DT than ST values 2–7 km above the primary tropopause, with the largest differences in winter. Large DT-ST differences extend to high NH latitudes in fall and winter, with longitudinal maxima in regions associated with enhanced wave activity and subtropical jet variations. Results for O 3 and HNO 3 agree closely between MLS and HIRDLS, and differences from ACE-FTS are consistent with its sparse and irregular midlatitude sampling. Consistent signatures in climatological trace gas fields provide strong evidence that transport from the tropical upper troposphere into the layer between double tropopauses is an important pathway for stratosphere-troposphere exchange.

Description: Airborne observations of fluorescent aerosol were made aboard an airship during CloudLab, a series of flights that took place in September and October of 2013 and covered a wide band of longitude across the continental US between Florida and California and between 28 and 37 N latitude. Sampling occurred from near the surface to 1000 m above the ground. A Wide-band Integrated Bioaerosol Sensor (WIBS-4) measured average concentrations of supermicron fluorescent particles aloft (1 µm to 10 µm), revealing number concentrations ranging from 2.1 ± 0.8 to 8.7 ± 2.2 × 10 4 particles m -3 and representing up to 24% of total supermicron particle number. We observed distinct variations in size distributions and fluorescent characteristics in different regions, and attribute these to geographically diverse bioaerosol. Fluorescent aerosol detected in the east is largely consistent with mold spores observed in a laboratory setting, while a shift to larger sizes associated with different fluorescent patterns is observed in the west. Fluorescent bioaerosol loadings in the desert west were as high as those near the Gulf of Mexico, suggesting that bioaerosol is a substantial component of supermicron aerosol both in humid and arid environments. The observations are compared to model fungal and bacterial loading predictions and good agreement in both particle size and concentrations is observed in the east. In the west, the model underestimated observed concentrations by a factor between 2 and 4 and the prescribed particle sizes are smaller than the observed fluorescent aerosol. A classification scheme for use with WIBS data is also presented.

Description: No abstract is available for this article.

Description: The impact of the tropical Pacific sea surface temperature (SST) anomaly on the winter mean surface air temperature (SAT) in the Asian-Pacific region is investigated during the period from 1948 to 2008 using both observations and a linear baroclinic model (LBM). A singular value decomposition (SVD) analysis is conducted between the 500-hPa geopotential height (Z500) over the Northern Hemisphere and the SST over the tropical Pacific Ocean to obtain the large scale atmospheric patterns related to tropical Pacific SST. Focus is given to the second pair of SVD mode (SVD2) which bears some similarities in the Z500 field to the Arctic Oscillation (AO) over the North Atlantic sector and can impact the SAT over a larger area of Asian-Pacific. In the winter of a positive SVD2 the SAT over the mid- to high-latitude Asian continent, the Arctic Ocean, the Indian Ocean and the western subtropical Pacific Ocean tend to be warmer-than-normal while the North Pacific Ocean around the Bering Strait is abnormally cold, and vice versa. Examination of the associated surface general circulation shows that a positive SVD2 tends to shift the Siberian High southward and the Aleutian low eastward resulting in anomalous weak pressure gradient between the Asian continent the North Pacific. Anomalous positive SLP anomalies around Japan and southerly wind along the east coast of the Asian continent are observed. At the same time, the East Asian trough at mid-troposphere becomes weaker-than-normal and the East Asian westerly jet stream is increased in magnitudes and shifted northward. The analysis of the wave activity flux and result of idealized numerical experiments show a possible influence of the western tropical Pacific SST forcing on the SVD2.

Description: This study presents a detailed cloud condensation nuclei (CCN) closure study that investigates the effects of chemical composition (bulk and size-resolved) and mixing state (internal and external) on CCN activity of aerosols. Measurements of the chemical composition, aerosol size distribution, total number concentration and CCN concentration at supersaturation (SS = 0.2 - 1.0%) were performed during the winter season in Kanpur, India. Among the two cases considered here, better closure results are obtained for case 1 (low total aerosol loading, 49.54±26.42 μ g m − 3 , and high O:C ratio, 0.61±0.07) compared to case 2 (high total aerosol loading, 101.05±18.73 μ g m − 3 , and low O:C ratio, 0.42±0.06), with a maximum reduction of 3-81% in CCN over-prediction for all depleted SS values (0.18 - 0.60%). Including the assumption that less volatile oxidized organic aerosols (LVOOA) represent the soluble organic fraction reduced the over-prediction to at most 40% and 129% in the internal and external mixing scenarios, respectively. At higher depleted SS values (0.34 - 0.60%), size-resolved chemical composition with an internal mixing state performed well in CCN closure among all organic solubility scenarios. However, at a lower depleted SS value (0.18%), closure is found to be more sensitive to both the chemical composition and mixing state of aerosols. At higher SS values, information on the solubility of organics and size-resolved chemical composition is required for accurate CCN predictions, whereas at lower SS values, information on the mixing state in addition to the solubility of organics and size-resolved chemical composition is required. Overall, κ total values are observed to be independent of the O:C ratio [ κ total = (0.36±0.01) × O:C - (0.03±0.01)] in the range of 0.2〈O:C〈0.81, which indicates that the variation in the chemical composition of aerosols is not well represented by the changes in the O:C ratio alone.

Description: A high-resolution transect of atmospheric soundings across the Kuroshio Current in the East China Sea was conducted onboard a ship in June 2012 with the objective of analyzing the influence of the complex sea surface temperature (SST) distribution on the Baiu frontal zone (BFZ). Expendable bathythermograph castings and continuous surface meteorological observations were also examined. Two distinct mesoscale atmospheric fronts, characterized by changes of wind direction in the lower troposphere and surface air temperature (SAT), were found in the BFZ. One (northern) atmospheric front was observed around the SST front in relation to a warm water tongue extending from the Kuroshio. A high SST region around the northern atmospheric front enhances unstable near surface stratification and intensifies turbulent heat flux. They help modify the marine atmospheric boundary layer in the BFZ. The other (southern) atmospheric front was at the southern end of the BFZ. Intense evaporation over the Kuroshio and moisture transport by southerly winds were important in forming the conditionally unstable air masses in the lower troposphere of the BFZ.

Description: We analyze the variability of mean age of air (AoA) and of the local effects of the stratospheric residual circulation and eddy mixing on AoA within the framework of the isentropic zonal mean continuity equation. AoA for the period 1988–2013 has been simulated with the Lagrangian chemistry transport model CLaMS driven by ERA-Interim winds and diabatic heating rates. Model simulated AoA in the lower stratosphere shows good agreement with both in-situ observations and satellite observations from MIPAS (Michelson Interferometer for Passive Atmospheric Sounding), even regarding interannual variability and changes during the last decade. The interannual variability throughout the lower stratosphere is largely affected by the QBO-induced circulation and mixing anomalies, with year-to-year AoA changes of about 0.5 years. The decadal 2002–2012 change shows decreasing AoA in the lowest stratosphere, below about 450 K. Above, AoA increases in the NH and decreases in the SH. Mixing appears to be crucial for understanding AoA variability, with local AoA changes resulting from a close balance between residual circulation and mixing effects. Locally, mixing increases AoA at low latitudes (40S-40N) and decreases AoA at higher latitudes. Strongest mixing occurs below about 500 K, consistent with the separation between shallow and deep circulation branches. The effect of mixing integrated along the air parcel path, however, significantly increases AoA globally, except in the polar lower stratosphere. Changes of local effects of residual circulation and mixing during the last decade are supportive of a strengthening shallow circulation branch in the lowest stratosphere and a southward shifting circulation pattern above.