Emission Of Longwave Radiation Research Articles

Comparison of Thermal Models for Ground-Mounted South-Facing Photovoltaic Technologies: A Practical Case Study

This paper examines the thermal properties of free-standing, ground-installed, south-facing crystalline and amorphous silicon photovoltaic modules, the remaining energy and the energy generation of the modules, in ideal and actual summer weather conditions. This work studies the algorithms in other studies used to describe the thermal processes occurring on the surface of photovoltaic modules. Using accurate devices and real, measured data, the deviations and the inaccuracies of theoretical approaches are investigated. The emphasis of the present study is to improve the simulation accuracy of the total emitted long-wave radiation at the module surface and to show the appropriate overall convection coefficient values for ground-mounted south-facing photovoltaic technologies. The innovative aspect of the present paper is an improved model resulting from an improved convective heat transfer and net long-wave radiation calculation. As a result of this research, algorithms describing the energy fluxes were developed. These algorithms have a 1–3% better accuracy of the net long-wave radiation calculations at the module surface. The rate of net energy exchange by convection at the module surface could be improved by 10–12% compared to the previous literature.

Spring Arctic Atmospheric Preconditioning: Do Not Rule Out Shortwave Radiation Just Yet

Abstract Springtime atmospheric preconditioning of Arctic sea ice for enhanced or buffered sea ice melt during the subsequent melt year has received considerable research focus. Studies have identified enhanced poleward atmospheric transport of moisture and heat during spring, leading to increased emission of longwave radiation to the surface. Simultaneously, these studies ruled out the role of shortwave radiation as an effective preconditioning mechanism because of relatively weak incident solar radiation, high surface albedo from sea ice and snow, and increased clouds during spring. These conclusions are derived primarily from atmospheric reanalysis, which may not always accurately represent the Arctic climate system. Here, top-of-atmosphere shortwave radiation observations from a state-of-the-art satellite sensor are compared with ERA-Interim reanalysis to examine similarities and differences in the springtime absorbed shortwave radiation (ASR) over the Arctic Ocean. Distinct biases in regional location and absolute magnitude of ASR anomalies are found between satellite-based measurements and reanalysis. Observations indicate separability between ASR anomalies in spring corresponding to anomalously low and high ice extents in September; the reanalysis fails to capture the full extent of this separability. The causes for the difference in ASR anomalies between observations and reanalysis are considered in terms of the variability in surface albedo and cloud presence. Additionally, biases in reanalysis cloud water during spring are presented and are considered for their impact on overestimating spring downwelling longwave anomalies. Taken together, shortwave radiation should not be overlooked as a contributing mechanism to springtime Arctic atmospheric preconditioning.

Lifetimes, direct and indirect radiative forcing, and global warming potentials of ethane (C2H6), propane (C3H8), and butane (C4H10)

The atmospheric abundance of the non‐methane volatile organic compounds (NMVOCs) ethane, propane, and butane increased during the industrial era. In addition to weak absorption and emission of longwave radiation, these gases influence the atmospheric radiative balance indirectly, mainly as precursors for ozone (O3), and through reaction with the hydroxyl radical (OH), which leads to less OH and thereby longer atmospheric lifetime of methane (CH4). In this study, we have calculated lifetimes, direct and indirect radiative forcing (RF), and global warming potentials (GWPs) for the three compounds, using a self‐consistent methodology. Results show net RF per unit emission of 1.0, 0.9, and 0.6 mW m−2 (Tg year−1)−1 for ethane, propane, and butane, respectively. For all compounds, the direct effect is considerably smaller than the indirect effects (6% or less of the total). The indirect O3 and CH4 effects are approximately of the same magnitude. Net GWPs for a 100‐year time horizon are 10 for ethane and propane, and 7 for butane, whereof the direct GWPs are <1 for all compounds. The net GWPs are generally higher than previous estimates, mainly because our calculations include emissions for a full year rather than one season. For the compounds studied here, 100‐year GWP values do not differ substantially between each compound, considering the large uncertainties involved, and this may indicate that using values representative for a lump of NMVOCs may be sufficient. However, the climate effects may differ more between NMVOC compounds other than alkanes, such as alkenes and aromatics.

An intermediate complexity AGCM simulations of climate response to a doubling of atmospheric carbon dioxide

Atmospheric response to doubled carbon dioxide concentration is estimated by analyzing 35-member ensemble mean made by an atmospheric general circulation model of intermediate complexity. Simulated changes in the mean fields are evaluated for winter (January-February-March) and summer (July-August- September) seasons. Results show that doubled CO2 concentration causes warming of around 2 °C at all levels in the model. At the surface, the largest temperature change is found over the polar areas; while at the higher levels considerable warming is found mostly over the continental parts. Atmospheric warming at the 300 hPa level is accompanied by cooling over the polar areas. At the levels above 300 hPa, temperature drops globally. Changes in jet stream occur at Northern Hemisphere with larger winter amplitudes. During the respective winter, stratiform precipitation significantly increases at the higher latitudes of both hemispheres and decreases mostly over the oceans. Over the Northern Hemisphere, convective precipitation is significantly increased during the summer. Over the southern part of tropical Pacific, stratiform and convective precipitation is decreased during the both seasons. Results also demonstrate that indirect impact of increased CO2 concentration (i.e. effects associated with changes in the lower boundary conditions) generally has a stronger contribution to the tropospheric warming than direct CO2 impact (i.e. the impact associated with absorption and emission of longwave radiation).

Quantifying radiation from thermal imaging of residential landscape elements

The microclimate of a residential landscape can affect both the energy use in your home and the human thermal comfort in your garden, ultimately affecting the heat in the neighbourhood or precinct. A thermal imaging camera provides information about the temperature of surfaces. By using Stefan–Boltzmann’s law and the surface properties, these temperatures can be used to calculate the emission of longwave radiation (radiant exitance) in W m−2. A thermal camera was used to determine the amount of radiant exitance from a range of residential landscape elements. A standard procedure for capturing these images was developed, taking into account factors which affect the quality of the radiometric data. A quantitative database comparing this radiation has been compiled for different times of day and different seasons. The sky view factor of these elements was chosen such that it was as close to 1 as possible. For a particular landscape design, areas of each landscape element can be measured and the amount of radiation reduced or emitted at different times can be calculated. This data can be used to improve landscape designs to reduce home energy use and human thermal comfort through shading and reduction of surfaces which emit longwave radiation close to the house.

A physically based 3‐D model of ice cliff evolution over debris‐covered glaciers

AbstractWe use high‐resolution digital elevation models (DEMs) from unmanned aerial vehicle (UAV) surveys to document the evolution of four ice cliffs on the debris‐covered tongue of Lirung Glacier, Nepal, over one ablation season. Observations show that out of four cliffs, three different patterns of evolution emerge: (i) reclining cliffs that flatten during the ablation season; (ii) stable cliffs that maintain a self‐similar geometry; and (iii) growing cliffs, expanding laterally. We use the insights from this unique data set to develop a 3‐D model of cliff backwasting and evolution that is validated against observations and an independent data set of volume losses. The model includes ablation at the cliff surface driven by energy exchange with the atmosphere, reburial of cliff cells by surrounding debris, and the effect of adjacent ponds. The cliff geometry is updated monthly to account for the modifications induced by each of those processes. Model results indicate that a major factor affecting the survival of steep cliffs is the coupling with ponded water at its base, which prevents progressive flattening and possible disappearance of a cliff. The radial growth observed at one cliff is explained by higher receipts of longwave and shortwave radiation, calculated taking into account atmospheric fluxes, shading, and the emission of longwave radiation from debris surfaces. The model is a clear step forward compared to existing static approaches that calculate atmospheric melt over an invariant cliff geometry and can be used for long‐term simulations of cliff evolution and to test existing hypotheses about cliffs' survival.

Polymictic pool behaviour in a montane meadow, Sierra Nevada, CA

AbstractWe observed polymictic behaviour in stream pools in Long Meadow, Sequoia National Park, California—part of the Southern Sierra Critical Zone Observatory. Stream pools stratified thermally during the day time and were isothermal at night—this pattern persists from the middle of summer into the fall. We found that four characteristics typical of a mountain meadow environment—low stream flow, open sky, cold groundwater discharge, and elevated organic carbon concentrations—are particularly conducive to pool stratification. Incoming shortwave radiation was the dominant energy input to heat pool water while nighttime emitted longwave radiation was the major cooling mechanism. Relatively cold groundwater discharge into the pool bottom increased density stratification within the pool. Elevated DOC concentrations increased the capacity of the pool to absorb photosynthetically active radiation and also promoted stratification. Stream velocities in the meadow were generally insufficient to meet threshold Richardson numbers and mix the pools during the daytime; smaller stream cross sectional areas would have potential for destabilizing pools in the daytime. We propose a conceptual model for describing polymictic stream pools and assessing the potential for polymictic pools to occur. Copyright © 2016 John Wiley & Sons, Ltd.

Influence of Cloud Microphysics and Radiation on Tropical Cyclone Structure and Motion

Abstract The authors survey a series of modeling studies that have examined the influences that cloud microphysical processes can have on tropical cyclone (TC) motion, the strength and breadth of the wind field, inner-core diabatic heating asymmetries, outer-core convective activity, and the characteristics of the TC anvil cloud. These characteristics are sensitive to the microphysical parameterization (MP) in large part owing to the cloud-radiative forcing (CRF), the interaction of hydrometeors with radiation. The most influential component of CRF is that due to absorption and emission of longwave radiation in the anvil, which via gentle lifting directly encourages the more extensive convective activity that then leads to a radial expansion of the TC wind field. On a curved Earth, the magnitude of the outer winds helps determine the speed and direction of TC motion via the beta drift. CRF also influences TC motion by determining how convective asymmetries develop in the TC inner core. Further improvements in TC forecasting may require improved understanding and representation of cloud-radiative processes in operational models, and more comprehensive comparisons with observations are clearly needed.

Review of wave‐turbulence interactions in the stable atmospheric boundary layer

AbstractFlow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods. Understanding turbulence intermittency and wave‐turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans. The stable atmospheric boundary layer (SABL) commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces, or even daytime over snow and ice surfaces, and when warm air is advected over cold surfaces. Intermittent turbulence intensification in the SABL impacts human activities and weather variability, yet it cannot be generated in state‐of‐the‐art numerical forecast models. This failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow, in which wave‐turbulence interaction is a potential mechanism for turbulence intermittency. A workshop on wave‐turbulence interactions in the SABL addressed the current understanding and challenges of wave‐turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory, observations, and numerical parameterization. There have been a number of reviews on waves, and a few on turbulence in stably stratified flows, but not much on wave‐turbulence interactions. This review focuses on the nocturnal SABL; however, the discussions here on intermittent turbulence and wave‐turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general.

Energy- and mass-balance comparison between Zhadang and Parlung No. 4 glaciers on the Tibetan Plateau

AbstractTibetan glaciers experience spatially heterogeneous changes, which call for further investigation of the mechanisms responsible from an energy and mass perspective. In this study, 2 year parallel observations (August 2010–July 2012) at 5665 m a.s.l. on Zhadang glacier (a subcontinental glacier) and 5202 m a.s.l. on Parlung No. 4 glacier (a maritime glacier) were used to reveal the drivers of surface energy and mass balance at these sites. Glacio-meteorological data show that air temperature and specific humidity were 1.7°C and 0.5 g kg−1lower on Zhadang glacier than on Parlung No. 4 glacier. The mass accumulation occurred primarily before the Indian summer monsoon onset on Parlung No. 4 glacier and after its onset on Zhadang glacier. Point net mass loss was 2.5 times larger on Parlung No. 4 glacier than on Zhadang glacier, mainly due to the difference in melt energy. Overall, the physical mechanisms controlling the mass and energy difference can be attributed to both the feedback role of surface albedo through different snow accumulation characteristics and longwave radiation emission of the atmosphere due to different meteorological backgrounds. Finally, a review of the few studies dealing with energy balance on the Tibetan glaciers describes the possible spatial characteristics requiring further investigation in the future on larger spatial and temporal scales.

Effects of Large Volcanic Eruptions on Global Summer Climate and East Asian Monsoon Changes during the Last Millennium: Analysis of MPI-ESM Simulations

Abstract Responses of summer [June–August (JJA)] temperature and precipitation to large volcanic eruptions are analyzed using the millennial simulations of the earth system model developed at the Max Planck Institute for Meteorology. The model was driven by up-to-date reconstructions of external forcing, including natural forcing (solar and volcanic) and anthropogenic forcing (land-cover change and greenhouse gases). Cooling anomalies after large volcanic eruptions are seen on a nearly global scale. The cooling in the Northern Hemisphere (NH) is stronger than in the Southern Hemisphere (SH), and cooling is stronger over the continents than over the oceans. The precipitation decreases in the tropical and subtropical regions in the first summer after large volcanic eruptions. The cooling, with amplitudes of up to −0.6°C, is also seen over eastern China. East Asia is dominated by northerly wind anomalies, and the corresponding summer rainfall exhibits a coherent reduction over the entirety of eastern China. The tropospheric mean temperature anomalies indicate that there is coherent cooling over East Asia and the tropical ocean after large volcanic eruptions. The cooling over the middle-to-high latitudes of East Asia is stronger than over the tropical ocean. This temperature anomaly pattern suggests a reduced land–sea thermal contrast and favors a weaker East Asian summer monsoon (EASM) circulation. Analysis of the radiative fluxes at the top of the atmosphere (TOA) suggests that the reduction in shortwave radiation after large volcanic eruptions is nearly twice as large as the reduction in emitted longwave radiation, a net loss of radiative energy that cools the surface and lower troposphere.

The Atmospheric Energy Constraint on Global-Mean Precipitation Change

Abstract Models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) robustly predict that the rate of increase in global-mean precipitation with global-mean surface temperature increase is much less than the rate of increase of water vapor. The goal of this paper is to explain in detail the mechanisms by which precipitation increase is constrained by radiative cooling. Changes in clear-sky atmospheric radiative cooling resulting from changes in temperature and humidity in global warming simulations are in good agreement with the multimodel, global-mean precipitation increase projected by GCMs (~1.1 W m−2 K−1). In an atmosphere with fixed specific humidity, radiative cooling from the top of the atmosphere (TOA) increases in response to a uniform temperature increase of the surface and atmosphere, while atmospheric cooling by exchange with the surface decreases because the upward emission of longwave radiation from the surface increases more than the downward longwave radiation from the atmosphere. When a fixed relative humidity (RH) assumption is made, however, uniform warming causes a much smaller increase of cooling at the TOA, and the surface contribution reverses to an increase in net cooling rate due to increased downward emission from water vapor. Sensitivity of precipitation changes to lapse rate changes is modest when RH is fixed. Carbon dioxide reduces TOA emission with only weak effects on surface fluxes, and thus suppresses precipitation. The net atmospheric cooling response and thereby the precipitation response to CO2-induced warming at fixed RH are mostly contributed by changes in surface fluxes. The role of clouds is discussed. Intermodel spread in the rate of precipitation increase across the CMIP5 simulations is attributed to differences in the atmospheric cooling.

Climate Feedbacks in CCSM3 under Changing CO2 Forcing. Part II: Variation of Climate Feedbacks and Sensitivity with Forcing

Abstract Are equilibrium climate sensitivity and the associated radiative feedbacks a constant property of the climate system, or do they change with forcing magnitude and base climate? Using the radiative kernel technique, feedbacks and climate sensitivity are evaluated in a fully coupled general circulation model (GCM) for three successive doublings of carbon dioxide starting from present-day concentrations. Climate sensitivity increases by 23% between the first and third CO2 doublings. Increases in the positive water vapor and cloud feedbacks are partially balanced by a decrease in the positive surface albedo feedback and an increase in the negative lapse rate feedback. Feedbacks can be decomposed into a radiative flux change and a climate variable response to temperature change. The changes in water vapor and Planck feedbacks are due largely to changes in the radiative response with climate state. Higher concentrations of greenhouse gases and higher temperatures lead to more absorption and emission of longwave radiation. Changes in cloud feedbacks are dominated by the climate response to temperature change, while the lapse rate and albedo feedbacks combine elements of both. Simulations with a slab ocean model (SOM) version of the GCM are used to verify whether an SOM-GCM accurately reproduces the behavior of the fully coupled model. Although feedbacks differ in magnitude between model configurations (with differences as large as those between CO2 doublings for some feedbacks), changes in feedbacks between CO2 doublings are consistent in sign and magnitude in the SOM-GCM and the fully coupled model.

LÉVY FLIGHT OF HOLES IN InP SEMICONDUCTOR SCINTILLATOR

High radiative efficiency in moderately doped n- InP results in the transport of holes dominated by photon-assisted hopping, when radiative hole recombination at one spot produces a photon, whose interband absorption generates another hole, possibly far away. Due to "heavy tails" in the hop probability, this is a random walk with divergent diffusivity (process known as the Lévy flight). Our key evidence is derived from the ratio of transmitted and reflected luminescence spectra, measured in samples of different thicknesses. These experiments prove the non-exponential decay of the hole concentration from the initial photo-excitation spot. The power-law decay, characteristic of Lévy flights, is steep enough at short distances (steeper than an exponent) to fit the data for thin samples and slow enough at large distances to account for thick samples. The high radiative efficiency makes possible a semiconductor scintillator with efficient photon collection. It is rather unusual that the material is "opaque" at wavelengths of its own scintillation. Nevertheless, after repeated recycling most photons find their way to one of two photodiodes integrated on both sides of the semiconductor slab. We present an analytical model of photon collection in two-sided slab, which shows that the heavy tails of Lévy-flight transport lead to a high charge collection efficiency and hence high energy resolution. Finally, we discuss a possibility to increase the slab thickness while still quantifying the deposited energy and the interaction position within the slab. The idea is to use a layered semiconductor with photon-assisted collection of holes in narrow-bandgap layers spaced by distances far exceeding diffusion length. Holes collected in these radiative layers emit longwave radiation, to which the entire structure is transparent. Nearly-ideal calculated characteristics of a mm-thick layered scintillator can be scaled up to several centimeters.

An alternative explanation of the semiarid urban area “oasis effect”

[1] This research evaluates the climatic summertime representation of the diurnal cycle of near-surface temperature using the Weather Research and Forecasting System (WRF) over the rapidly urbanizing and water-vulnerable Phoenix metropolitan area. A suite of monthly, high-resolution (2 km grid spacing) simulations are conducted during the month of July with both a contemporary landscape and a hypothetical presettlement scenario. WRF demonstrates excellent agreement in the representation of the daily to monthly diurnal cycle of near-surface temperatures, including the accurate simulation of maximum daytime temperature timing. Thermal sensitivity to anthropogenic land use and land cover change (LULCC), assessed via replacement of the modern-day landscape with natural shrubland, is small on the regional scale. The WRF-simulated characterization of the diurnal cycle, supported by previous observational analyses, illustrates two distinct and opposing impacts on the urbanized diurnal cycle of the Phoenix metro area, with evening and nighttime warming partially offset by daytime cooling. The simulated nighttime urban heat island (UHI) over this semiarid urban complex is explained by well-known mechanisms (slow release of heat from within the urban fabric stored during daytime and increased emission of longwave radiation from the urban canopy toward the surface). During daylight hours, the limited vegetation and dry semidesert region surrounding metro Phoenix warms at greater rates than the urban complex. Although prior work has suggested that daytime temperatures are lower within the urban complex owing to the addition of residential and agricultural irrigation (i.e., “oasis effect”) we show that modification of Phoenix's surrounding environment to a biome more representative of temperate regions eliminates the daytime urban cooling. Our results indicate that surrounding environmental conditions, including land cover and availability of soil moisture, play a principal role in establishing the nature and evolution of the diurnal cycle of near-surface temperature for the greater Phoenix, Arizona, metropolitan area relative to its rural and undeveloped counterpart.

Paired comparison of water, energy and carbon exchanges over two young maritime pine stands (Pinus pinaster Ait.): effects of thinning and weeding in the early stage of tree growth

The effects of management practices on energy, water and carbon exchanges were investigated in a young pine plantation in south-west France. In 2009-10, carbon dioxide (CO(2)), H(2)O and heat fluxes were monitored using the eddy covariance and sap flow techniques in a control plot (C) with a developed gorse layer, and an adjacent plot that was mechanically weeded and thinned (W). Despite large differences in the total leaf area index and canopy structure, the annual net radiation absorbed was only 4% lower in plot W. We showed that higher albedo in this plot was offset by lower emitted long-wave radiation. Annual evapotranspiration (ET) from plot W was 15% lower, due to lower rainfall interception and transpiration by the tree canopy, partly counterbalanced by the larger evaporation from both soil and regrowing weedy vegetation. The drainage belowground from plot W was larger by 113 mm annually. The seasonal variability of ET was driven by the dynamics of the soil and weed layers, which was more severely affected by drought in plot C. Conversely, the temporal changes in pine transpiration and stem diameter growth were synchronous between sites despite higher soil water content in the weeded plot. At the annual scale, both plots were carbon sinks, but thinning and weeding reduced the carbon uptake by 73%: annual carbon uptake was 243 and 65 g C m(-2) on plots C and W, respectively. Summer drought dramatically impacted the net ecosystem exchange: plot C became a carbon source as the gross primary production (GPP) severely decreased. However, plot W remained a carbon sink during drought, as a result of decreases in both GPP and ecosystem respiration (R(E)). In winter, both plots were carbon sources, plots C and W emitting 67.5 and 32.4 g C m(-2), respectively. Overall, this study highlighted the significant contribution of the gorse layer to mass and energy exchange in young pine plantations.

Habitable Zone Limits for Dry Planets

Most discussion of habitable planets has focused on Earth-like planets with globally abundant liquid water. For an "aqua planet" like Earth, the surface freezes if far from its sun, and the water vapor greenhouse effect runs away if too close. Here we show that "land planets" (desert worlds with limited surface water) have wider habitable zones than aqua planets. For planets at the inner edge of the habitable zone, a land planet has two advantages over an aqua planet: (i) the tropics can emit longwave radiation at rates above the traditional runaway limit because the air is unsaturated and (ii) the dry air creates a dry stratosphere that limits hydrogen escape. At the outer limits of the habitable zone, the land planet better resists global freezing because there is less water for clouds, snow, and ice. Here we describe a series of numerical experiments using a simple three-dimensional global climate model for Earth-sized planets. Other things (CO(2), rotation rate, surface pressure) unchanged, we found that liquid water remains stable at the poles of a low-obliquity land planet until net insolation exceeds 415 W/m(2) (170% that of modern Earth), compared to 330 W/m(2) (135%) for the aqua planet. At the outer limits, we found that a low-obliquity land planet freezes at 77%, while the aqua planet freezes at 90%. High-obliquity land and aqua planets freeze at 58% and 72%, respectively, with the poles offering the last refuge. We show that it is possible that, as the Sun brightens, an aqua planet like Earth can lose most of its hydrogen and become a land planet without first passing through a sterilizing runaway greenhouse. It is possible that Venus was a habitable land planet as recently as 1 billion years ago.

Forests and Climate: A Warming Paradox

![Figure][1] Yatir forest. In their Report, Rotenberg and Yakir studied the semi-arid Yatir forest in Israel. CREDIT: THE WEIZMANN INSTITUTE E. Rotenberg and D. Yakir (“Contribution of semi-arid forests to the climate system,” Reports, 22 January, p. [451][2]) showed that forestation may not be an effective tool for climate change mitigation. They found that in a semi-arid landscape, the warming potential of a forest due to changes in the surface albedo and the longwave radiation emission far outweighs the cooling effect due to carbon sequestration. However, their analysis did not address the fact that the radiation balance of the surface is not the same as the radiation balance of the climate system. The atmosphere retains a significant portion of the longwave radiation emitted and the shortwave radiation reflected by the surface. Globally, only 10% of the surface longwave radiation escapes the atmosphere to the outer space ([ 1 ][3]). The escape fraction over Rotenberg and Yakir's site is probably higher due to low cloud cover, but not by much: The outgoing longwave radiation for a clear sky at the top of the atmosphere suggests a maximum of 20% ([ 2 ][4]). Similarly, because of atmospheric absorption and cloud reflection, the local albedo at the top of the atmosphere is lower than the surface value. By not taking into account this energy redistribution, Rotenberg and Yakir may have substantially overestimated the warming effect of forestation (and the cooling effect of desertification). A deeper issue, also related to energy redistribution, is whether it is accurate to combine the CO2 radiative forcing and the surface radiation change for the purpose of analysis. To help policy discussions, the greenhouse effects are often expressed as climate sensitivity ([ 3 ][5]), estimated at ∼0.8°C increase in the surface temperature per W m−2 increase in the radiative forcing ([ 4 ][6]). The surface exchange process does not work that way. Rotenberg and Yakir's paradoxical result—that the forest, being an efficient convector, is much cooler despite more radiation loading than the shrubland—provides a powerful argument against combining the two quantities. In humid climates, forests also cool the surface by removing its latent heat, which is released above the atmospheric boundary layer by cloud condensation. 1. [↵][7]1. K. E. Trenberth 2. et al ., Bull. Am. Meteorol. Soc. 90, 331 (2009). [OpenUrl][8] 2. [↵][9]1. S. K. Yang 2. et al ., J. Clim. 12, 477 (1999). [OpenUrl][10][CrossRef][11] 3. [↵][12]1. V. Ramanthan, 2. G. Carmichael , Nat. Geosci. 1, 221 (2008). [OpenUrl][13][CrossRef][14] 4. [↵][15]1. S. Solomon IPCC, Summary for Policymakers (SPM), in Climate Change 2007: The Physical Science Basis: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, S. Solomon et al ., Eds. (Cambridge Univ. Press, New York, 2007). [1]: pending:yes [2]: /lookup/doi/10.1126/science.1179998 [3]: #ref-1 [4]: #ref-2 [5]: #ref-3 [6]: #ref-4 [7]: #xref-ref-1-1 View reference 1 in text [8]: {openurl}?query=rft.jtitle%253DBull.%2BAm.%2BMeteorol.%2BSoc.%26rft.volume%253D90%26rft.spage%253D331%26rft.atitle%253DBULL%2BAM%2BMETEOROL%2BSOC%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [9]: #xref-ref-2-1 View reference 2 in text [10]: {openurl}?query=rft.jtitle%253DJ.%2BClim.%26rft.volume%253D12%26rft.spage%253D477%26rft_id%253Dinfo%253Adoi%252F10.1175%252F1520-0442%25281999%2529012%253C0477%253AEOTERB%253E2.0.CO%253B2%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [11]: /lookup/external-ref?access_num=10.1175/1520-0442(1999)012 2.0.CO;2&link_type=DOI [12]: #xref-ref-3-1 View reference 3 in text [13]: {openurl}?query=rft.jtitle%253DNat.%2BGeosci.%26rft.volume%253D1%26rft.spage%253D221%26rft_id%253Dinfo%253Adoi%252F10.1038%252Fngeo156%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [14]: /lookup/external-ref?access_num=10.1038/ngeo156&link_type=DOI [15]: #xref-ref-4-1 View reference 4 in text

A new one-dimensional radiative equilibrium model for investigating atmospheric radiation entropy flux

A new one-dimensional radiative equilibrium model is built to analytically evaluate the vertical profile of the Earth's atmospheric radiation entropy flux under the assumption that atmospheric longwave radiation emission behaves as a greybody and shortwave radiation as a diluted blackbody. Results show that both the atmospheric shortwave and net longwave radiation entropy fluxes increase with altitude, and the latter is about one order in magnitude greater than the former. The vertical profile of the atmospheric net radiation entropy flux follows approximately that of the atmospheric net longwave radiation entropy flux. Sensitivity study further reveals that a 'darker' atmosphere with a larger overall atmospheric longwave optical depth exhibits a smaller net radiation entropy flux at all altitudes, suggesting an intrinsic connection between the atmospheric net radiation entropy flux and the overall atmospheric longwave optical depth. These results indicate that the overall strength of the atmospheric irreversible processes at all altitudes as determined by the corresponding atmospheric net entropy flux is closely related to the amount of greenhouse gases in the atmosphere.

Record low surface air temperature at Vostok station, Antarctica

The lowest recorded air temperature at the surface of the Earth was a measurement of −89.2°C made at Vostok station, Antarctica, at 0245 UT on 21 July 1983. Here we present the first detailed analysis of this event using meteorological reanalysis fields, in situ observations and satellite imagery. Surface temperatures at Vostok station in winter are highly variable on daily to interannual timescales as a result of the great sensitivity to intrusions of maritime air masses as Rossby wave activity changes around the continent. The record low temperature was measured following a near‐linear cooling of over 30 K over a 10 day period from close to mean July temperatures. The event occurred because of five specific conditions that arose: (1) the temperature at the core of the midtropospheric vortex was at a near‐record low value; (2) the center of the vortex moved close to the station; (3) an almost circular flow regime persisted around the station for a week resulting in very little warm air advection from lower latitudes; (4) surface wind speeds were low for the location; and (5) no cloud or diamond dust was reported above the station for a week, promoting the loss of heat to space via the emission of longwave radiation. We estimate that should a longer period of isolation occur the surface temperature at Vostok could drop to around −96°C. The higher site of Dome Argus is typically 5–6 K colder than Vostok so has the potential to record an even lower temperature.