Air-snow exchange investigations at Summit, Greenland: An overview

The Greenland Ice Sheet Project 2 (GISP2) and Greenland Ice Core Project (GRIP) deep drilling programs at Summit, Greenland included support (both logistical and scientific) of extensive investigation of atmospheric transport and air-snow exchange processes of gases and particles relevant to the interpretation of the ice-core records. Much of the sampling for the air-snow exchange investigations was conducted at a unique solar-powered camp 30 km southwest of the GISP2 drill camp (even further from the GRIP camp) and was characterized by a high degree of international collaboration and cooperation. The wide range of expertise and analytical capabilities of the 20-plus investigators participating in these studies has provided important insight into the meteorological, physical, and chemical processes which interact to determine the composition of snow and firn at Summit. Evolving understanding of this system will allow improved reconstruction of the composition of the atmosphere over Greenland in the past from the detailed Summit ice-core records. This paper provides an overview of air-snow exchange investigations at Summit, including their development through the course of the drilling programs (1989–1993), significant findings related to both air-snow exchange issues and the present state of the Arctic free troposphere, as well as the major outstanding questions which are being addressed in ongoing experiments at Summit

SEASONAL LABOR CONSTRAINTS AND INTRA-HOUSEHOLD DYNAMICS IN THE FEMALE FIELDS OF SOUTHERN CAMEROON

Women's agricultural production is modeled as a sequential switching regression process determined by men's clearing labor capacity and women's harvest labor capacity. Results show that output was more often constrained by husband's clearing labor. However, men's economic contribution to household consumption is inversely related to women's agricultural output.agriculture, seasonal labor, gender, production, developing countries, Consumer/Household Economics, International Development, Labor and Human Capital,

Beryllium 7 and Lead 210 in the western hemisphere Arctic atmosphere: Observations from three recent aircraft-based sampling programs

Concentrations of the natural radionuclides 7Be and 210Pb were determined in aerosol samples collected in the western hemisphere Arctic during the recent NOAA Arctic Gas and Aerosol Sampling Program (AGASP 3) and NASA Global Tropospheric Experiment/Arctic Boundary Layer Expeditions (GTE/ABLE 3A and ABLE 3B) missions. Beryllium 7 showed a free tropospheric concentration maximum between 4 and 5 km in the summer of 1990. Previous 7Be data obtained in the late 1950s and early 1960s also indicated a similar vertical distribution of 7Be near 70°N. Injection of stratospheric air through tropopause folds associated with the Arctic jet near 70°N appears to explain the presence of a layer of air near 4–5 km in the high Arctic free troposphere with elevated 7Be concentrations. The vertical distribution of 210Pb showed a distinct difference between the high-Arctic and sub-Arctic in the summer of 1988. At latitudes greater than 65°N, 210Pb concentrations at 3–6 km were elevated compared to those below 1 km. The reverse of this trend was observed near 60°N. These same vertical distributions were also apparent in aerosol SO42−, determined in separate aerosol samples collected on the same flights (Talbot et al., this issue). The results for 210Pb suggest that some of the difference between the summer troposphere in the high- and sub-Arctic is also due to enhanced stratosphere-troposphere exchange in the vicinity of the Arctic jet. These observations, and other findings from ABLE 3A presented in this issue, suggest that for some species the stratosphere may be a principal source influencing their distribution in the Arctic summer troposphere. For example, intrusions of stratospheric air constitute the dominant source term for tropospheric budgets of 7Be and ozone, and may be important in the 210Pb, SO42−, and NOybudgets. Further investigation, including determination of detailed 7Be and 210Pb distributions, is needed to quantify the stratospheric impact on the chemistry of the Arctic troposphere during the summer

A three-loop check of the 'a - maximization' in SQCD with adjoint(s)

The 'a - maximization' was introduced by K. Inrtiligator and B. Wecht for finding anomalous dimensions of chiral superfields at the IR fixed points of the RG flow. Using known explicit calculations of anomalous dimensions in the perturbation theory of SQCD (with one or two additional adjoint fields), it is checked here at the three-loop level.Comment: 5 pages; the title changed, the text improved and expande

PrAGMATiC: a Probabilistic and Generative Model of Areas Tiling the Cortex

Much of the human cortex seems to be organized into topographic cortical maps. Yet few quantitative methods exist for characterizing these maps. To address this issue we developed a modeling framework that can reveal group-level cortical maps based on neuroimaging data. PrAGMATiC, a probabilistic and generative model of areas tiling the cortex, is a hierarchical Bayesian generative model of cortical maps. This model assumes that the cortical map in each individual subject is a sample from a single underlying probability distribution. Learning the parameters of this distribution reveals the properties of a cortical map that are common across a group of subjects while avoiding the potentially lossy step of co-registering each subject into a group anatomical space. In this report we give a mathematical description of PrAGMATiC, describe approximations that make it practical to use, show preliminary results from its application to a real dataset, and describe a number of possible future extensions

Utility Functions of Equivalent Form and the Effect of Parameter Changes on Optimum Decision Making

We derive a class of utility functions that are equivalent with respect to a well-defined functional form. We study the case of constant relative risk aversion (of some order) to investigate on different equivalence relations in order to determine the, possibly infinite, number of equivalence classes when utility functions satisfy a specific form. Then we apply our results to standard applications in economics and finance, for example, to the effect of price volatility on optimum hedging. --equivalence class,risk aversion,sensitivity analysis

The preservation of atmospheric nitrate in snow at Summit, Greenland

There is great interest in using nitrate NO3 isotopic composition in ice cores to track the history of precursor nitrogen oxides (NOx = NO + NO2) in the atmosphere. Nitrate NO3 however can be lost from the snow by surface processes, such as photolysis back to NOx upon exposure to sunlight, making it difficult to interpret records of NO3 as a tracer of atmospheric NOx loading. In a campaign consisting of two field seasons (May–June) at Summit, Greenland, high temporal frequency surface snow samples were collected and analyzed for the oxygen isotopic composition of NO3. The strong, linear relationship observed between the oxygen isotopes of NO3 in both 2010 and 2011, is difficult to explain in the presence of significant post depositional processing of NO3 unless several unrelated variables change in concert. Therefore, the isotopic signature of NO3 in the snow at Summit is most feasibly explained as preserved atmospheric NO3 deposition

U.S. HOUSEHOLD CONSUMPTION OF FRESH FRUITS

This study uses the 1987-88 U.S. Department of Agriculture Nationwide Food Consumption Survey data to analyze the impacts of income, prices, and selected socioeconomic characteristics on household consumption of fresh fruits. Results suggest that fresh fruits are considered economic necessities, with own prices significantly influencing consumption. Cross-price effects are generally weak and insignificant, but the number of adults in the age group 18-64 is an important determinant of household consumption of fresh fruits. While nutrition information and household savings have significant, positive influences on most fresh fruit consumption, the presence of a working wife has a significant and negative influence.Food Consumption/Nutrition/Food Safety,

Sulfate and MSA in the air and snow on the Greenland Ice Sheet

Sulfate and methanesulfonic acid (MSA) concentrations in aerosol, surface snow, and snowpit samples have been measured at two sites on the Greenland Ice Sheet. Seasonal variations of the concentrations observed for these chemical species in the atmosphere are reproduced in the surface snow and preserved in the snowpit sequence. The amplitude of the variations over a year are smaller in the snow than in the air, but the ratios of the concentrations are comparable. The seasonal variations for sulfate are different at the altitude of the Ice Sheet compared to those observed at sea level, with low concentrations in winter and short episodes of elevated concentrations in spring. In contrast, the variations in concentrations of MSA are similar to those measured at sea level, with a first sequence of elevated concentrations in spring and another one during summer, and a winter low resulting from low biogenic production. The ratio MSA/sulfate clearly indicates the influence of high-latitude sources for the summer maximum of MSA, but the large impact of anthropogenic sulfate precludes any conclusion for the spring maximum. The seasonal pattern observed for these species in a snowpit sampled according to stratigraphy indicates a deficit in the accumulation of winter snow at the summit of the Greenland Ice Sheet, in agreement with some direct observations. A deeper snowpit covering the years 1985–1992 indicates the consistency of the seasonal pattern for MSA over the years, which may be linked to transport and deposition processes

Organic Price Premiums Paid for Fresh Tomatoes and Apples by U.S. Households: Evidence from Nielsen Homescan Data

Using multivariate regression on data composed of prices, produce characteristics, demographics, and interactions, this study investigates organic price premiums paid by U.S. consumers for fresh tomatoes and apples, two of the top organic produce sellers, and identifies factors explaining variation in price premiums. The econometric problem of each buyer having multiple records in the purchase data is addressed in the estimation procedure.Consumer/Household Economics, Food Consumption/Nutrition/Food Safety,