43,632 research outputs found
On the meaning of feedback parameter, transient climate response, and the greenhouse effect: Basic considerations and the discussion of uncertainties
In this paper we discuss the meaning of feedback parameter, greenhouse effect
and transient climate response usually related to the globally averaged energy
balance model of Schneider and Mass. After scrutinizing this model and the
corresponding planetary radiation balance we state that (a) the this globally
averaged energy balance model is flawed by unsuitable physical considerations,
(b) the planetary radiation balance for an Earth in the absence of an
atmosphere is fraught by the inappropriate assumption of a uniform surface
temperature, the so-called radiative equilibrium temperature of about 255 K,
and (c) the effect of the radiative anthropogenic forcing, considered as a
perturbation to the natural system, is much smaller than the uncertainty
involved in the solution of the model of Schneider and Mass. This uncertainty
is mainly related to the empirical constants suggested by various authors and
used for predicting the emission of infrared radiation by the Earth's skin.
Furthermore, after inserting the absorption of solar radiation by atmospheric
constituents and the exchange of sensible and latent heat between the Earth and
the atmosphere into the model of Schneider and Mass the surface temperatures
become appreciably lesser than the radiative equilibrium temperature. Moreover,
neither the model of Schneider and Mass nor the Dines-type two-layer energy
balance model for the Earth-atmosphere system, both contain the planetary
radiation balance for an Earth in the absence of an atmosphere as an asymptotic
solution, do not provide evidence for the existence of the so-called
atmospheric greenhouse effect if realistic empirical data are used.Comment: 69 pages, 3 tables and 16 figure
Earth radiation budget measurement from a spinning satellite: Conceptual design of detectors
The conceptual design, sensor characteristics, sensor performance and accuracy, and spacecraft and orbital requirements for a spinning wide-field-of-view earth energy budget detector were investigated. The scientific requirements for measurement of the earth's radiative energy budget are presented. Other topics discussed include the observing system concept, solar constant radiometer design, plane flux wide FOV sensor design, fast active cavity theory, fast active cavity design and error analysis, thermopile detectors as an alternative, pre-flight and in-flight calibration plane, system error summary, and interface requirements
Perspectives of current-layer diagnostics in solar flares
A reconnecting current layer is a `heart' of a solar flare, because it is a
place of magnetic-field energy release. However there are no direct
observations of these layers. The aim of our work is to understand why we
actually do not directly observe current layers and what we need to do it in
the future. The method is based on a simple mathematical model of a super-hot
(T ~ 1E8 K) turbulent-current layer (SHTCL) and a model of plasma heating by
the layer. The models allow us to study a correspondence between the main
characteristics of the layer, such as temperature and dimensions, and the
observational features, such as differential and integral emission measure of
heated plasma, intensity of spectral lines Fe XXVI (1.78 and 1.51A) and Ni
XXVII (1.59 A). This method provides a theoretical basis for determining
parameters of the current layer from observations. Observations of SHTCLs are
difficult, because the spectral line intensities are faint, but it is
theoretically possible in the future. Observations in X-ray range 1.5--1.8 A
with high spectral resolution (better than 0.01 A) and high temporal resolution
(seconds) are needed. It is also very important to interpret the observations
using a multi-temperature approach instead of the usual single or double
temperature method
Challenges for the Accurate Determination of the Surface Thermal Condition via In-Depth Sensor Data
The overall goal of this work is to provide a systematic methodology by which the difficulties associated with the inverse heat conduction problem (IHCP) can be resolved. To this end, two inverse heat conduction methods are presented. First, a space-marching IHCP method (discrete space, discrete time) utilizing a Gaussian low-pass filter for regularization is studied. The stability and accuracy of this inverse prediction is demonstrated to be more sensitive to the temporal mesh than the spatial mesh. The second inverse heat conduction method presented aims to eliminate this feature by employing a global time, discrete space inverse solution methodology. The novel treatment of the temporal derivative in the heat equation, combined with the global time Gaussian low-pass filter provides the regularization required for stable, accurate results.
A physical experiment used as a test bed for validation of the numerical methods described herein is also presented. The physics of installed thermocouple sensors are outlined, and loop-current step response (LCSR) is employed to measure and correct for the delay and attenuation characteristics of the sensors. A new technique for the analysis of LCSR data is presented, and excellent agreement is observed between this model and the data.
The space-marching method, global time method, and a new calibration integral method are employed to analyze the experimental data. First, data from only one probe is used which limits the results to the case of a semi-infinite medium. Next, data from two probes at different depths are used in the inverse analysis which enables generalization of the results to domains of finite width. For both one- and two-probe analyses, excellent agreement is found between the actual surface heat flux and the inverse predictions. The most accurate inverse technique is shown to be the calibration integral method, which is presently restricted to one-probe analysis. It is postulated that the accuracy of the global time method could be improved if the required higher-time derivatives of temperature data could be more accurately measured. Some preliminary work in obtaining these higher-time derivatives of temperature from a voltage-rate interface used in conjunction with the thermocouple calibration curve is also presented
ACBAR: The Arcminute Cosmology Bolometer Array Receiver
We describe the Arcminute Cosmology Bolometer Array Receiver (ACBAR); a
multifrequency millimeter-wave receiver designed for observations of the Cosmic
Microwave Background (CMB) and the Sunyaev-Zel'dovich effect in clusters of
galaxies. The ACBAR focal plane consists of a 16-pixel, background-limited, 240
mK bolometer array that can be configured to observe simultaneously at 150,
220, 280, and 350 GHz. With 4-5' FWHM Gaussian beam sizes and a 3 degree
azimuth chop, ACBAR is sensitive to a wide range of angular scales. ACBAR was
installed on the 2 m Viper telescope at the South Pole in January 2001. We
describe the design of the instrument and its performance during the 2001 and
2002 observing seasons.Comment: 59 pages, 16 figures -- updated to reflect version published in ApJ
Atmospheric Circulation of Terrestrial Exoplanets
The investigation of planets around other stars began with the study of gas
giants, but is now extending to the discovery and characterization of
super-Earths and terrestrial planets. Motivated by this observational tide, we
survey the basic dynamical principles governing the atmospheric circulation of
terrestrial exoplanets, and discuss the interaction of their circulation with
the hydrological cycle and global-scale climate feedbacks. Terrestrial
exoplanets occupy a wide range of physical and dynamical conditions, only a
small fraction of which have yet been explored in detail. Our approach is to
lay out the fundamental dynamical principles governing the atmospheric
circulation on terrestrial planets--broadly defined--and show how they can
provide a foundation for understanding the atmospheric behavior of these
worlds. We first survey basic atmospheric dynamics, including the role of
geostrophy, baroclinic instabilities, and jets in the strongly rotating regime
(the "extratropics") and the role of the Hadley circulation, wave adjustment of
the thermal structure, and the tendency toward equatorial superrotation in the
slowly rotating regime (the "tropics"). We then survey key elements of the
hydrological cycle, including the factors that control precipitation, humidity,
and cloudiness. Next, we summarize key mechanisms by which the circulation
affects the global-mean climate, and hence planetary habitability. In
particular, we discuss the runaway greenhouse, transitions to snowball states,
atmospheric collapse, and the links between atmospheric circulation and CO2
weathering rates. We finish by summarizing the key questions and challenges for
this emerging field in the future.Comment: Invited review, in press for the Arizona Space Science Series book
"Comparative Climatology of Terrestrial Planets" (S. Mackwell, M. Bullock,
and J. Harder, editors). 56 pages, 26 figure
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