ALBERT

Description: Abstract Coeval changes in atmospheric CO2 and 14C contents during the last deglaciation are often attributed to ocean circulation changes that released carbon stored in the deep ocean during the Last Glacial Maximum (LGM). Work is being done to generate records that allow for the identification of the exact mechanisms leading to the accumulation and release of carbon from the oceanic reservoir, but these mechanisms are still the subject of debate. Here we present foraminifera 14C data from five cores in a transect across the Chilean continental margin between ~540 m and ~3100 m depth spanning the last 20,000 years. Our data reveal that during the LGM waters at ~2000 m were 50 to 80 % more depleted in Δ14C than waters at ~1500 m when compared to modern values, consistent with the hypothesis of a glacial deep–ocean carbon reservoir that was isolated from the atmosphere. During the deglaciation, our intermediate water records reveal homogenization in the Δ14C values between ~800 and ~1500 m from ~16.5–14.5 ka cal BP to ~14‐12 ka cal BP, which we interpret as deeper penetration of Antarctic Intermediate Water. While many questions still remain, this process could aid the ventilation of the deep ocean at the beginning of the deglaciation, contributing to the observed ~40 ppm rise in atmospheric pCO2.

Description: [1]  Paleoceanographic archives derived from seventeen marine sediment cores reconstruct the response of the SW Pacific Ocean to the peak interglacial, Marine Isotope Stage (MIS) 5e (ca. 125 ka). Paleo-Sea Surface Temperature (SST) estimates were obtained from the Random Forest model – an ensemble decision tree tool - applied to core-top planktonic foraminiferal faunas calibrated to modern SSTs. The reconstructed geographic pattern of the SST anomaly (maximum SST between 120-132 ka minus mean modern SST) seems to indicate how MIS 5e conditions were generally warmer in the southwest Pacific, especially in the western Tasman Sea where a strengthened East Australian Current (EAC) likely extended subtropical influence to ca. 45 o S off Tasmania. In contrast, the eastern Tasman Sea may have had a modest cooling except around 45 o S. The observed pattern resembles that developing under the present warming trend in the region. An increase in wind stress curl over the modern South Pacific is hypothesized to have spun-up the South Pacific Subtropical Gyre, with concurrent increase in subtropical flow in the western boundary currents that include the EAC. However, warmer temperatures along the subtropical front and Campbell Plateau to the south suggest the relative influence of the boundary inflows to eastern New Zealand may have differed in MIS 5e, and these currents may have followed different paths compared to today.

Description: The study uses a Monte Carlo radiative transfer model to examine the sensitivity of the UV Erythemal radiation (UVER) enhancement to broken liquid water clouds of the cumulus and stratocumulus type. The model uses monochromatic radiation at 310 nm corresponding approximately to the peak of the product between irradiance and the erythemal curve. All scattering, absorption, extinction coefficients and spectral albedos are tuned to this wavelength. In order of importance, fractional cloud cover, the area of individual cloud patches and cloud thickness exert a strong influence on the enhancement, with smaller contributions from cloud optical depth, cloud base height and solar zenith angle. In order to produce realistic enhancements for our study area located in the Valencia region of Spain (39° 30’ N; 0° 25’W), measurements were obtained from a Landsat image of the region in combination with a spectral Fourier transform model. The Monte Carlo model, as applied to the Fourier transform cloud distribution, produced satisfactory results compared to one year of measured UVER enhancement for the study region provided fractional cloud cover was equal to or greater than 3/10. At smaller cloud fractions, the neglect of cloud patches less than 50 m x 50 m in area by the model created significant discrepancies.

Description: The urban population of South America has grown at 1.05% per year, greater urbanization increasing problems related to air pollution. In most large cities in South America, there has been no continuous long-term measurement of regulated pollutants. One exception is São Paulo, Brazil, where an air quality-monitoring network has been in place since the 1970s. In this paper, we used an air quality-based approach to determine pollutant trends for emissions of carbon monoxide (CO), nitrogen oxides (NO x ), ozone (O 3 ) and coarse particulate matter (PM 10 ), mostly from mobile sources, in the Metropolitan Region of São Paulo (MRSP) for the 2000–2013 period. Mobile sources included light-duty vehicles (LDVs, comprising gasoline- or ethanol-powered cars and motorcycles) and heavy-duty vehicles (HDVs, comprising diesel-powered trucks and buses). Pollutant concentrations for mobile source emissions were measured and correlated with fuel sales by the emission factors. Over the 2000–2013 period, concentrations of NO x , CO, and PM 10 decreased by 0.65, 0.37, and 0.71% month −1 , respectively, whereas sales of gasoline, ethanol, and diesel increased by 0.26, 1.96, and 0.38% month −1 , respectively. LDVs were the major mobile source of CO, whereas LDVs were the major source of NO x and PM 10 . Increases in fuel sales and in the corresponding traffic volume were partially offset by decreases in pollutant concentrations. Between 2000 and 2013, there was a sharp (−5 ppb month −1 ) decrease in the concentrations of LDV-emitted CO, together with (less dramatic) decreases in the concentrations of HDV-emitted NO x and PM 10 (−0.25 and −0.09 ppb month −1 , respectively). Variability was greater for HDV-emitted NO x and PM 10 (R = −0.47 and −0.41, respectively) than for LDV-emitted CO (R = −0.72). We draw the following conclusions: the observed concentrations of LDV-emitted CO decreased at a sharper rate than did those of HDV-emitted NO x and PM 10 ; mobile source contributions to O 3 formation varied significantly, LDVs making a greater contribution during the 2000–2008 period, whereas HDVs made a greater contribution during the 2009–2013 period; and decreases in NO x emissions resulted in increases in O 3 observations.

Description: We examine in detail a one-year global reanalysis of carbon monoxide (CO) that is based on joint assimilation of conventional meteorological observations and Measurement of Pollution in The Troposphere (MOPITT) multispectral CO retrievals in the Community Earth System Model (CESM). Our focus is to assess the impact to the chemical system when CO distribution is constrained in a coupled full chemistry-climate model like CESM. To do this, we first evaluate the joint reanalysis (MOPITT Reanalysis) against four sets of independent observations and compare its performance against a reanalysis with no MOPITT assimilation (Control Run). We then investigate the CO burden and chemical response with the aid of tagged sectoral CO tracers. We estimate the total tropospheric CO burden in 2002 (from ensemble mean and spread) to be 371 ±12% Tg for MOPITT Reanalysis and 291 ± 9 % Tg for Control Run. Our multi-species analysis of this difference suggests that: a) direct emissions of CO and hydrocarbons are too low in the inventory used in this study; and b) chemical oxidation, transport, and deposition processes are not accurately and consistently represented in the model. Increases in CO led to net reduction of OH and subsequent longer lifetime of CH 4 (Control Run: 8.7 years versus MOPITT Reanalysis: 9.3 years). Yet, at the same time, this increase led to 5-10% enhancement of northern hemisphere O 3 and overall photochemical activity via HO X recycling. Such nonlinear effects further complicate the attribution to uncertainties in direct emissions alone. This has implications to chemistry-climate modeling and inversion studies of longer-lived species.

Description: In a sediment core from the Pacific sector of the Antarctic Zone of the Southern Ocean (AZ), we report diatom-bound N isotope (δ 15 N db ) records for total recoverable diatoms and two distinct diatom assemblages (pennate- and centric-rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ 15 N db (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal- and barium-based proxies for reduced export production during ice ages, the δ 15 N db increases point to ice age reductions in the supply of deep ocean-sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ 15 N db changes are not the result of changing species composition. The pennate and centric assemblage δ 15 N db records indicate similar changes, but with a significant decline in their difference during peak ice ages. A tentative seasonality-based interpretation of the centric-to-pennate δ 15 N db difference suggests that late summer surface waters became nitrate-free during the peak glacials.

Description: [1]  Validation results are reported for the MOPITT (Measurements of Pollution in the Troposphere) “Version 5” (V5) product for tropospheric carbon monoxide (CO) and are compared to results for the “Version 4” product. The V5 retrieval algorithm introduces (1) a method for reducing retrieval bias drift associated with long-term instrumental degradation, (2) a more exact representation of the effects of random errors in the radiances and, for the first time, (3) the use of MOPITT's near-infrared (NIR) radiances to complement the thermal-infrared (TIR) radiances. Exploiting TIR and NIR radiances together facilitates retrievals of CO in the lowermost troposphere. V5 retrieval products based (1) solely on TIR measurements, (2) solely on NIR measurements and (3) on both TIR and NIR measurements are separately validated and analyzed. Actual retrieved CO profiles and total columns are compared with equivalent retrievals based on in-situ measurements from (1) routine NOAA aircraft sampling mainly over North America and (2) the “HIAPER Pole to Pole Observations” (HIPPO) field campaign. Particular attention is focused on the long-term stability and geographical uniformity of the retrieval errors. Results for the retrieved total column clearly indicate reduced temporal bias drift in the V5 products compared to the V4 product, and do not exhibit a positive bias in the Southern Hemisphere which is evident in the V4 product.

Description: On 21 August 2009, the Airborne Detector for Energetic Lightning Emissions (ADELE), an array of six gamma-ray detectors, detected a brief burst of gamma rays while flying aboard a Gulfstream V jet near two active thunderstorm cells. The duration and spectral characteristics of the event are consistent with the terrestrial gamma ray flashes (TGFs) seen by instruments in low Earth orbit. A long-duration, complex +IC flash was taking place in the nearer cell at the same time, at a distance of ∼10 km from the plane. The sferics that are probably associated with this flash extended over 54 ms and included several ULF pulses corresponding to charge moment changes of up to 30 C km, this value being in the lower half of the range of sferics associated with TGFs seen from space. Monte Carlo simulations of gamma ray propagation in the Earth's atmosphere show that a TGF of normal intensity would, at this distance, have produced a gamma ray signal in ADELE of approximately the size and spectrum that was actually observed. We conclude that this was the first detection of a TGF from an aircraft. We show that because of the distance, ADELE's directional and spectral capabilities could not strongly constrain the source altitude of the TGF but that such constraints would be possible for TGFs detected at closer range.

Description: Abstract The values of the atmospheric variables follow from mass, momentum and energy conservation equations. These equations involve gradients which, in heterogeneous terrain, lead to a connection of the values at one point to the values in their nearby surroundings, due to turbulence mixing or advective local transports. In this work the observed variability of the air and soil variables is analysed for a 1 km2 surface in a semi‐rural area for a number of weather stations separated typically 150 m. Data show a large variability at the hectometre scale, with several degrees of difference in temperature sustained in time between neighbouring points. While in the daytime turbulence contributes to keep the differences moderate, in weak wind nights the spatial variability increases significantly. The variability of soil variables can be large depending on the soil moisture and the vegetation cover and is less sensitive to the diurnal cycle. The inspection of the vertical gradients of temperature and humidity reveals that their sign and intensity, and consequently the corresponding sensible and latent heat fluxes, differ depending on the measuring point. The thermal advection is obtained from the hectometre‐scale network, which is comparable in magnitude to the turbulent fluxes and to the imbalance of the surface energy budget for clear and calm nights. During the day, the advection term may explain part of the energy budget imbalance, particularly when it is computed on a 30‐minute time scale. A similar method is applied to the water vapour, finding that in the very dry conditions of the experiment, moisture advection is significant and with values comparable to the evapotranspiration.

Description: The paper explores methods of partitioning the hourly average UV erythemal flux into its direct and diffuse components for Valencia, Spain. It is shown that the cloud modification factor, the ratio of measured to cloudless erythemal flux relates linearly to the fraction of the measured irradiance that is diffuse. This relationship was developed further into two simple models- a linear and nonlinear one. The models are characterized by an effective cloud cover to partition the global erythemal flux. The diffuse fraction increases linearly with cloud cover in the linear model, but exponentially in the nonlinear one. The models may be used to partition the direct and diffuse irradiance with RMS errors values ranging from 5.7 to 6.8 mWm−2 and 6.0–7.7 mWm−2 for direct and diffuse, respectively, with the nonlinear model performing best overall.