122 research outputs found
Spectroscopy of the Methane {\nu}3 Band with an Accurate Mid-Infrared Coherent Dual- Comb Spectrometer
We demonstrate a high-accuracy dual-comb spectrometer centered at 3.4 \mu m.
The amplitude and phase spectra of the P, Q, and partial R-branch of the
methane {\nu}3 band are measured at 25 MHz to 100 MHz point spacing with ~kHz
resolution and a signal-to-noise ratio of up to 3500. A fit of the absorbance
and phase spectra yield the center frequency of 132 rovibrational lines. The
systematic uncertainty is estimated to be 300 kHz, which is 10-3 of the Doppler
width and a tenfold improvement over Fourier transform spectroscopy. These data
are the first high- accuracy molecular spectra obtained with a direct comb
spectrometer.Comment: journal articl
The Role of Sulfur Dioxide in Stratospheric Aerosol Formation Evaluated by Using in situ Measurements in the Tropical Lower Stratosphere
Stratospheric aerosols (SAs) are a variable component of the Earth\u27s albedo that may be intentionally enhanced in the future to offset greenhouse gases (geoengineering). The role of tropospheric-sourced sulfur dioxide (SO2) in maintaining background SAs has been debated for decades without in situ measurements of SO2 at the tropical tropopause to inform this issue. Here we clarify the role of SO2 in maintaining SAs by using new in situ SO2 measurements to evaluate climate models and satellite retrievals. We then use the observed tropical tropopause SO2 mixing ratios to estimate the global flux of SO2 across the tropical tropopause. These analyses show that the tropopause background SO2 is about 5 times smaller than reported by the average satellite observations that have been used recently to test atmospheric models. This shifts the view of SO2 as a dominant source of SAs to a near-negligible one, possibly revealing a significant gap in the SA budget. ©2017. American Geophysical Union
Following wrong suggestions: self-blame in human and computer scenarios
This paper investigates the specific experience of following a suggestion by
an intelligent machine that has a wrong outcome and the emotions people feel.
By adopting a typical task employed in studies on decision-making, we presented
participants with two scenarios in which they follow a suggestion and have a
wrong outcome by either an expert human being or an intelligent machine. We
found a significant decrease in the perceived responsibility on the wrong
choice when the machine offers the suggestion. At present, few studies have
investigated the negative emotions that could arise from a bad outcome after
following the suggestion given by an intelligent system, and how to cope with
the potential distrust that could affect the long-term use of the system and
the cooperation. This preliminary research has implications in the study of
cooperation and decision making with intelligent machines. Further research may
address how to offer the suggestion in order to better cope with user's
self-blame.Comment: To be published in the Proceedings of IFIP Conference on
Human-Computer Interaction (INTERACT)201
Estimating vehicle carbon dioxide emissions from Boulder, Colorado, using horizontal path-integrated column measurements
We performed 7.5 weeks of path-integrated concentration
measurements of CO2, CH4, H2O, and HDO over the city of Boulder, Colorado. An open-path dual-comb spectrometer simultaneously
measured time-resolved data across a reference path, located near the
mountains to the west of the city, and across an over-city path that
intersected two-thirds of the city, including two major commuter arteries. By
comparing the measured concentrations over the two paths when the wind is
primarily out of the west, we observe daytime CO2 enhancements over
the city. Given the warm weather and the measurement footprint, the dominant
contribution to the CO2 enhancement is from city vehicle traffic. We
use a Gaussian plume model combined with reported city traffic patterns to
estimate city emissions of on-road CO2 as (6.2±2.2) × 105 metric tons (t) CO2 yr−1
after correcting for non-traffic sources. Within the uncertainty, this value
agrees with the city's bottom-up greenhouse gas inventory for the on-road
vehicle sector of 4.5×105 t CO2 yr−1. Finally, we
discuss experimental modifications that could lead to improved estimates from
our path-integrated measurements.</p
Chemistry–climate model simulations of twenty-first century stratospheric climate and circulation changes
The response of stratospheric climate and circulation to increasing amounts of greenhouse gases (GHGs) and ozone recovery in the twenty-first century is analyzed in simulations of 11 chemistry–climate models using near-identical forcings and experimental setup. In addition to an overall global cooling of the stratosphere in the simulations (0.59 6 0.07 K decade21 at 10 hPa), ozone recovery causes a warming of the Southern Hemisphere polar lower stratosphere in summer with enhanced cooling above. The rate of warming correlates with the rate of ozone recovery projected by the models and, on average, changes from 0.8 to 0.48 Kdecade21 at 100 hPa as the rate of recovery declines from the first to the second half of the century. In the winter northern polar lower stratosphere the increased radiative cooling from the growing abundance of GHGs is, in most models, balanced by adiabatic warming from stronger polar downwelling. In the Antarctic lower stratosphere the models simulate an increase in low temperature extremes required for polar stratospheric cloud (PSC) formation, but the positive trend is decreasing over the twenty-first century in all models. In the Arctic, none of the models simulates a statistically significant increase in Arctic PSCs throughout the twenty-first century. The subtropical jets accelerate in response to climate change and the ozone recovery produces awestward acceleration of the lower-stratosphericwind over theAntarctic during summer, though this response is sensitive to the rate of recovery projected by the models. There is a strengthening of the Brewer–Dobson circulation throughout the depth of the stratosphere, which reduces the mean age of air nearly everywhere at a rate of about 0.05 yr decade21 in those models with this diagnostic. On average, the annual mean tropical upwelling in the lower stratosphere (;70 hPa) increases by almost 2% decade21, with 59% of this trend forced by the parameterized orographic gravity wave drag in the models. This is a consequence of the eastward acceleration of the subtropical jets, which increases the upward flux of (parameterized) momentum reaching the lower stratosphere in these latitudes
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