Climate Lecture 4: Atmospheric Radiation

The climate system is well known for its great complexity and complex interactions that involve dynamic, thermodynamic, radiative, chemical, biological and human-driven processes. This view of the climate system has emerged from detailed measurements, meticulous record keeping, and theoretical analyses arising from, and made possible by the science and technology revolution that greatly advanced our understanding the role of physical processes that operate in the global climate system. These measurements also show very clearly that the global surface temperature has been rising over the past century, and that this is a consequence of human industrial activity

Analysis of normal and strong - lined K - type dwarf and giant stars

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. In this work a detailed analysis is carried out for twenty-six normal and super-metal-rich (SMR) K dwarfs and giants in the solar neighborhood. The observational material consists of line measurements on tracings of high dispersion spectra along with photoelectric scans covering a wide range of wavelengths. The program Atlas was employed to construct the model atmospheres; the temperature fit was provided by a matching of the predicted continua to the de-blanketed scans. H[...] wing profiles were also used to obtain information on the temperatures. The major conclusions that were reached are the following: 1) A gravity defect sets in at about spectral type K2 in both dwarfs and giants; its nature is such that progressively lower gravities are required in order to obtain equal ion and neutral abundances as one goes to cooler stars. In the coolest stars the spectroscopic gravities imply masses lower than 0.1M[...]. It is suggested that the effect may be caused by a new opacity source that is acting to steepen the spectral gradient in the visual and near-infrared, thereby falsifying the temperatures. The dependence of the unknown absorber on the temperature and gravity. are discussed and a rough formula describing this dependence is given. It is shown that the new opacity also explains various discrepancies noted by other observers. 2) The SMR stars are generally overabundant by about 0.2 - 0.3 dex relative to the normal-abundance comparison stars of the same temperature. An overabundance of sodium by about 0.5 dex is found for all the SMR stars, with the exception of the dwarf 54 Psc, which is found to have essentially normal metal abundances. [...]UMi, the coolest giant in the program, is also the most super-metal-rich, with a general overabundance of about 0.4 dex and a sodium enhancement of 0.8 dex. The iron overabundance is rather marginal in most of the giants ([...]). 3) No correlation is found between metal abundance and turbulence. In particular, the SMR stars in this program are not found to possess high microturbulent velocities. The U-B deficiencies can be explained by the effects of a slight metal enhancement on the colors (Strom et al. 1971) and the line blocking due to the CN violet system. 4) The SMR dwarfs all lie high on the main sequence, in keeping with their derived metal abundances. It is not necessary to invoke substantial variations in helium content to account for their positions

Global Warming in the Twenty-First Century: An Alternative Scenario

A common view is that the current global warming rate will continue or accelerate. But we argue that rapid warming in recent decades has been driven mainly by non-CO2 greenhouse gases (GHGs), such as chlorofluorocarbons, CH4, and N2O, not by the products of fossil fuel burning, CO2 and aerosols, the positive and negative climate forcings of which are partially offsetting. The growth rate of non-CO2 GHGs has declined in the past decade. If sources of CH4 and O3 precursors were reduced in the future, the change in climate forcing by non-CO2 GHGs in the next 50 years could be near zero. Combined with a reduction of black carbon emissions and plausible success in slowing CO2 emissions, this reduction of non-CO2 GHGs could lead to a decline in the rate of global warming, reducing the danger of dramatic climate change. Such a focus on air pollution has practical benefits that unite the interests of developed and developing countries. However, assessment of ongoing and future climate change requires composition specific long-term global monitoring of aerosol properties

Columnar water vapor retrievals from multifilter rotating shadowband radiometer data

[1] The multifilter rotating shadowband radiometer (MFRSR) measures direct and diffuse irradiances in the visible and near-infrared spectral range. In addition to characteristics of atmospheric aerosols, MFRSR data also allow retrieval of precipitable water vapor (PWV) column amounts, which are determined from the direct normal irradiances in the 940-nm spectral channel. The HITRAN 2004 spectral database was used in our retrievals to model the water vapor absorption. We present a detailed error analysis describing the influence of uncertainties in instrument calibration and spectral response, as well as those in available spectral databases, on the retrieval results. The results of our PWV retrievals from the Southern Great Plains (SGP) site operated by the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program were compared with correlative standard measurements by microwave radiometers (MWRs) and a global positioning system (GPS) water vapor sensor, as well as with retrievals from other solar radiometers (AERONET's CIMEL, AATS-6). Some of these data are routinely available at the SGP's Central Facility; however, we also used measurements from a wider array of instrumentations deployed at this site during the water vapor intensive observation period (WVIOP2000) in September-October 2000. The WVIOP data show better agreement between different solar radiometers or between different microwave radiometers (both groups showing relative biases within 4%) than between these two groups of instruments, with MWR values being consistently higher (up to 14%) than those from solar instruments (especially in the large PWV column amount range). We also demonstrate the feasibility of using MFRSR network data for creation of 2D data sets comparable with that of the MODIS satellite water vapor product

The role of long-lived greenhouse gases as principal LW control knob that governs the global surface temperature for past and future climate change

The climate system of the Earth is endowed with a moderately strong greenhouse effect that is characterised by non-condensing greenhouse gases (GHGs) that provide the core radiative forcing. Of these, the most important is atmospheric CO2. There is a strong feedback contribution to the greenhouse effect by water vapour and clouds that is unique in the solar system, exceeding the core radiative forcing due to the non-condensing GHGs by a factor of three. The significance of the non-condensing GHGs is that once they have been injected into the atmosphere, they remain there virtually indefinitely because they do not condense and precipitate from the atmosphere, their chemical removal time ranging from decades to millennia. Water vapour and clouds have only a short lifespan, with their distribution determined by the locally prevailing meteorological conditions, subject to Clausius–Clapeyron constraint. Although solar irradiance is the ultimate energy source that powers the terrestrial greenhouse effect, there has been no discernable long-term trend in solar irradiance since precise monitoring began in the late 1970s. This leaves atmospheric CO2 as the effective control knob driving the current global warming trend. Over geological time scales, volcanoes are the principal source of atmospheric CO2, and the weathering of rocks is the principal sink, with the biosphere participating as both a source and a sink. The problem at hand is that human industrial activity is causing atmospheric CO2, to increase by 2 ppm yr−1, whereas the interglacial rate has been 0.005 ppm yr−1. This is a geologically unprecedented rate to turn the CO2 climate control knob. This is causing the global warming that threatens the global environment

GISS‐E2.1: Configurations and Climatology

Abstract This paper describes the GISS‐E2.1 contribution to the Coupled Model Intercomparison Project, Phase 6 (CMIP6). This model version differs from the predecessor model (GISS‐E2) chiefly due to parameterization improvements to the atmospheric and ocean model components, while keeping atmospheric resolution the same. Model skill when compared to modern era climatologies is significantly higher than in previous versions. Additionally, updates in forcings have a material impact on the results. In particular, there have been specific improvements in representations of modes of variability (such as the Madden‐Julian Oscillation and other modes in the Pacific) and significant improvements in the simulation of the climate of the Southern Oceans, including sea ice. The effective climate sensitivity to 2 × CO2 is slightly higher than previously at 2.7–3.1°C (depending on version) and is a result of lower CO2 radiative forcing and stronger positive feedbacks