The relative effect of solar altitude on surface temperatures and energy budget components on two contrasting landscapes

A solar radiation attenuation model has been combined with a steady-state surface energy budget model. The combined model was programmed to investigate the resultant surface temperatures and associated, causal energy budget components to changes in solar altitudes and air temperatures. Two contrasting landscape scenarios were investigated: a barren and a grassy plain, under cloudless skies. Solutions to these many computations are presented in graphical form in order to gain an improved perspective of the varied responses of changing surface temperatures and energy budgets as complex functions of different solar angles and air temperature regimes. The grassy landscape was much more conservative in its reaction to the forcing by these two environmental parameters. It is believed that the portrayed trends encompass the possible extremes encountered in a continuum of landscapes in the real world.Dr. O'Rourke is currently a Post-Doctoral Scholar at UCLA.     

Simulation of daily energy budget and mean soil temperatures at an arid site

Summary Soil temperature is often inadequately based upon relatively few measurements at widely dispersed locations. Within arid regions, such as the desert southwestern United States, soils, microclimates, and thus soil temperature may be markedly heterogeneous. Because extensive measurement of soil temperature is often not feasible, models are needed that simulate soil temperature based on readily available soil survey and above-ground weather information. This paper describes a simple energy-budget based model for simulating daily mean temperatures within a bare arid land soil. The model requires basic information on soil physical properties, and daily weather data including air temperature, windspeed, rainfall, and solar radiation to calculate daily surface energy budget components and surface temperature. One of two alternative numerical methods is then used to calculated subsurface temperatures. Tests of the model using 1987 daily temperature data from an arid site at Yuma, Arizona resulted in root mean square deviations within 1.4°C between daily modeled and measured temperatures at both 0.05 and 0.10 m depths. Sensitivity analysis showed modeled temperatures at 0.05 m depth to be most sensitive to parameters affecting the surface energy balance such as air temperature and solar radiation. Modeled temperatures at 1.0m depth were relatively more sensitive to initial temperature conditions and to parameters affecting distribution of energy within the profile such as thermal conductivity.With 3 Figures     

A transitioning Arctic surface energy budget: the impacts of solar zenith angle, surface albedo and cloud radiative forcing

Snow surface and sea-ice energy budgets were measured near 87.5°N during the Arctic Summer Cloud Ocean Study (ASCOS), from August to early September 2008. Surface temperature indicated four distinct temperature regimes, characterized by varying cloud, thermodynamic and solar properties. An initial warm, melt-season regime was interrupted by a 3-day cold regime where temperatures dropped from near zero to ?7°C. Subsequently mean energy budget residuals remained small and near zero for 1 week until once again temperatures dropped rapidly and the energy budget residuals became negative. Energy budget transitions were dominated by the net radiative fluxes, largely controlled by the cloudiness. Variable heat, moisture and cloud distributions were associated with changing air-masses. Surface cloud radiative forcing, the net radiative effect of clouds on the surface relative to clear skies, is estimated. Shortwave cloud forcing ranged between ?50 W m^?2 and zero and varied significantly with surface albedo, solar zenith angle and cloud liquid water. Longwave cloud forcing was larger and generally ranged between 65 and 85 W m^?2, except when the cloud fraction was tenuous or contained little liquid water; thus the net effect of the clouds was to warm the surface. Both cold periods occurred under tenuous, or altogether absent, low-level clouds containing little liquid water, effectively reducing the cloud greenhouse effect. Freeze-up progression was enhanced by a combination of increasing solar zenith angles and surface albedo, while inhibited by a large, positive surface cloud forcing until a new air-mass with considerably less cloudiness advected over the experiment area.     

有限区域湿有效能量的层结、斜压、正压分量及其收支方程

本文探讨了将湿有效能量分解成层结、斜压、正压分量的方法,并讨论了它们的收支方程式.其中层结分量与实际大气中对流不稳定有较好的对应关系,但在干有效位能中分解不出这一项.在斜压、正压分量的收支方程中,除附加项外都与干有效位能的方程类似.由三个分量的收支方程看出,湿有效能量向动能的转换只可能发生在层结不稳定或(与)有斜压存在的大气中.这与天气分析经验以及经典的马古列斯(M.Margules)模式是一致的.     

On dynamic and thermodynamic components of cloud changes

Clouds are sensitive to changes in both the large-scale circulation and the thermodynamic structure of the atmosphere. In the tropics, temperature changes that occur on seasonal to decadal time scales are often associated with circulation changes. Therefore, it is difficult to determine the part of cloud variations that results from a change in the dynamics from the part that may result from the temperature change itself. This study proposes a simple framework to unravel the dynamic and non-dynamic (referred to as thermodynamic) components of the cloud response to climate variations. It is used to analyze the contrasted response, to a prescribed ocean warming, of the tropically-averaged cloud radiative forcing (CRF) simulated by the ECMWF, LMD and UKMO climate models. In each model, the dynamic component largely dominates the CRF response at the regional scale, but this is the thermodynamic component that explains most of the average CRF response to the imposed perturbation. It is shown that this component strongly depends on the behaviour of the low-level clouds that occur in regions of moderate subsidence (e.g. in the trade wind regions). These clouds exhibit a moderate sensitivity to temperature changes, but this is mostly their huge statistical weight that explains their large influence on the tropical radiation budget. Several propositions are made for assessing the sensitivity of clouds to changes in temperature and in large-scale motions using satellite observations and meteorological analyses on the one hand, and mesoscale models on the other hand.     

Further notes on a feature of leaf and air temperatures

Summary This is a sequel to an earlier paper, in which it was pointed out that there is a tendency for the temperature of leaves of many well-watered plants, exposed to midday sunshine, to exceed the ambient temperature only when the latter is below a so-called equality temperature. Further evidence is presented here, again indicating that equality temperatures are often in the vicinity of 30°C.

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Zusammenfassung Der vorliegende Artikel stellt die Fortsetzung einer früheren Arbeit dar, in der dargelegt wurde, da? eine Tendenz dazu besteht, da\ die Temperature der Bl?tter vieler Pflanzen, denen hinreichend Wasser zur Verfügung steht und die der Mittagssonne ausgesetzt sind, nur dann h?her ist als die Umgebungstemperatur, wenn die letztere niedriger ist als die sogenannte „Gleichheitstemperatur”; das ist die Temperatur, bei der kein Flu? fühlbarer W?rme zwischen Blatt und Umgebung auftritt. Es werden Beispiele angeführt, die zeigen, da? die Gleichheitstemperatur nahe bei 30°C liegt.

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Résumé Le présent mémoire est la suite d'un précédent dans lequel on avait émis l'avis que la température des feuilles de bien des plantes exposées au soleil de midi ne dépassait la température ambiante que si cette dernière était inférieure à une certaine “température d'égalité” (Gleichheitstemperatur). Cette tendance ne se manifeste cependant que si les dites plantes disposent de suffisamment d'eau. La “température d'égalité” est celle à laquelle on ne constate pas de flux de chaleur sensible entre la feuille et le milieu ambiant. On donne ici des exemples supplémentaires qui montrent que cette “température d'égalité” est souvent proche de 30°C.

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With 5 Figures     

An energy budget for waves and turbulence within an inversion

Several features of the maintenance of breaking gravity waves and turbulence in a marine inversion are examined. A formulation is proposed for a critical Richardson number based on a mutual response of the mean and turbulent states to a wave-like disturbance. The energy balance, based on averaged aircraft soundings, is examined to ascertain the order of magnitude of the component terms in the vicinity of a contemporaneous radar echo. Some physical mechanisms are discussed which may explain some aspects of the sustained existence of the echo layers.After preparation of this paper, a considerable number of pertinent and up-dated results bearing on waves and turbulence in stable layers were published as Volume 4 ofBoundary-Layer Meteorology, April 1973. The present discussion should be considered in relation to these papers and of Gossardet al. (1973) and Metcalf and Atlas (1973) in particular.     

Estimating heat fluxes by merging profile formulae and the energy budget with a variational technique

A variational technique (VT) is applied to estimate surface sensible and latent heat fluxes based on observations of air temperature, wind speed, and humidity, respectively, at three heights (1 m, 4 m, and 10 m), and the surface energy and radiation budgets by the surface energy and radiation system (SERBS). The method fully uses all information provided by the measurements of air temperature, wind, and humidity profiles, the surface energy budget, and the similarity profile formulae as well. Data collected at Feixi experiment station installed by the China Heavy Rain Experiment and Study (HeRES) Program are used to test the method. Results show that the proposed technique can overcome the well-known unstablility problem that occurs when the Bowen method becomes singular; in comparison with the profile method, it reduces both the sensitivities of latent heat fluxes to observational errors in humidity and those of sensible heat fluxes to observational errors in temperature, while the estimated heat fluxes approximately satisfy the surface energy budget. Therefore, the variational technique is more reliable and stable than the two conventional methods in estimating surface sensible and latent heat fluxes.     

The effects of changing solar angles,cloud regimes,and air temperatures on the temperatures of contrasting surfaces

A steady-state energy budget and a solar radiation-cloud attenuation model have been linked. This has permitted a systematic examination of the changing relative surface temperatures and differences between surface and air temperatures as functions of varying solar altitudes, selected cloud types, cloud covers, and air temperatures. This analysis was performed for two contrasting surfaces: barren and grassy. The results are presented in a series of three-dimensional graphs. The grassy landscape reacted more conservatively to changing solar altitudes (for all cloud types and amounts) compared with the barren surface. The results are assumed to encompass most of the possible extremes encountered in real landscapes exposed to similar changes in solar angle, air temperatures, and cloud regimes.Dr. O'Rourke is currently a Post-Doctoral Scholar at UCLA.     

西太平洋热带地区能量和热量的总收支——中美西太平洋海-气合作考察观测事实之五

根据“向阳红14号”考察船在中美海-气考察第一次航程(1986年2月8—14日)所获取的水文气象和日射观测资料,以及特定区域内站点的海洋气象资料,探讨了热带西太平洋有限区域内下垫面和大气的冷、热源以及海气系统向周围大气的能量水平输送的源、汇问题。分析计算指出,在考察期间热带西太平洋地区是一个热量积贮区。     

Arctic aerosol and Arctic climate: Results from an energy budget model

An energy budget model is used to study the effect on Arctic climate of optically active aerosol in the Arctic atmosphere. The dependence of the change in surface temperature on the vertical distribution of the aerosol and on the radiative properties of the aerosol-free atmosphere, the Arctic surface, and the aerosol, itself, are calculated. An extensive sensitivity analysis is performed to assess the degree to which the results of the model are dependent upon the assumptions underlying it.List of Symbols Used I ₀ Solar flux at the top of the Arctic Atmosphere (Arctic here means 70° N latitude to the pole) - a _S Surface albedo of the Arctic (a _S ^c is the value of surface albedo at which the sign of the surface temperature perturbation changes) - Reflection coefficient of the aerosol-free Arctic atmosphere - Absorption coefficient of the aerosol-free Arctic atmosphere - Transmission coefficient of the aerosol-free Arctic atmosphere - RI ₀ Total flux of sunlight reflected from the Arctic - A _A I ₀ Total flux of sunlight absorbed in the Arctic atmosphere - A _S I ₀ Total flux of sunlight absorbed at the Arctic surface - A _aer I ₀ Total flux of sunlight absorbed in the Arctic aerosol - Q _A Net atmospheric flow of energy, per unit of Arctic surface area, north across 70° N latitude - Q _S Net oceanic flow of energy, per unit of Arctic surface area, north across 70° N latitude - E Convective plus latent heat fluxes from surface to atmosphere - F _A Net flow of energy to the Arctic atmosphere - F _S Net flow of energy to the Arctic surface - T _A An effective temperature of the Arctic atmosphere - T _S Surface temperature of the Arctic - w Single-scattering albedo of the aerosol - t Optical depth of the aerosol - g Fraction of incident radiation scattered forward by the aerosol - Reflection coefficient of the aerosol - Absorption coefficient of the aerosol - Transmission coefficient of the aerosol - p,q Number of atmospheric layers and the inverse of the fraction of incident IR absorbed in each layer in the energy budget model - F,G,H Measures of the amount of IR-active atmosphere above the surface, the aerosol, and the clouds     

Recent changes of the tropical water and energy budget and of midlatitude circulations

Rising atmospheric H₂O content and temperature above the tropical Pacific (Hense et al. 1988) stimulated research on tropical ocean-atmosphere fluxes in the belt 10° S-14° N, based on COADS data for 1949–1979. Increasing sea-surface temperature was accompanied by regionally varying increases in the air-sea temperature and humidity gradients. The apparent rise in wind speed appeared to be only partly biased. Using several assumptions of the wind speed trend, increasing evaporation was found nearly everywhere. The best estimates vary regionally between 7% and 15%, with highest values above the warmest oceans between longitude 66° E and the date line. In the Atlantic, freshening surface waters (Levitus 1989) also suggest an increase of precipitation. Conversion of zonally averaged results into global estimates led to a rise of the energy input into the atmosphere, with a most plausible value of 8–10 W/m². Since large-scale sea-surface warming appears to be induced by the greenhouse effect of CO₂ combined with other trace gases, a powerful feedback mechanism — including H₂O phase changes — should be responsible for the intensification of the hydrological cycle. This energy input of tropical origin seems to be larger — by a factor near 4 — than the dry greenhouse effect. Such a well-founded conjecture of increasing internal/potential energy in the tropics suggests a similar rise of kinetic energy within the extratropical atmospheric circulation. This can be checked on the basis of daily operational hemispheric analyses of the German Weather Service, here using the period October 1961–March 1988. During the cold season they show, at the surface, a deepening of the Icelandic and Aleutian Lows by 6 and 10 hPa, respectively, and at the 50 kPa level an amplification of the baroclinic westerlies by 20–40%. Upper wind observation series have been used to check this strengthening of the westerlies and an expansion of the Aleutian Low. During the warm season, weaker changes in opposite directions are observed. While the observed facts are incompatible with many of the recent climate models, a few models (Wilson and Mitchell 1987, Hansen et al. 1988) using an advanced parameterization of tropical convection support the evolution of a powerful tropical heat source centred within mid-tropospheric layers.     

The atmospheric energy budget and implications for surface fluxes and ocean heat transports

Comprehensive diagnostic comparisons and evaluations have been carried out with the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and European Centre for Medium Range Weather Forecasts (ECMWF) reanalyses of the vertically integrated atmospheric energy budgets. For 1979 to 1993 the focus is on the monthly means of the divergence of the atmospheric energy transports. For February 1985 to April 1989, when there are reliable top-of-the-atmosphere (TOA) radiation data from the Earth Radiation Budget Experiment (ERBE), the implied monthly mean surface fluxes are derived and compared with those from the assimilating models and from the Comprehensive Ocean Atmosphere Data Set (COADS), both locally and zonally integrated, to deduce the implied ocean meridional heat transports. While broadscale aspects and some details of both the divergence of atmospheric energy and the surface flux climatological means are reproducible, especially in the zonal means, differences are also readily apparent. Systematic differences are typically ∼20 W m⁻². The evaluation highlights the poor results over land. Land imbalances indicate local errors in the divergence of the atmospheric energy transports for monthly means on scales of 500 km (T31) of 30 W m⁻² in both reanalyses and ∼50 W m⁻² in areas of high topography and over Antarctica for NCEP/NCAR. Over the oceans in the extratropics, the monthly mean anomaly time series of the vertically integrated total energy divergence from the two reanalyses correspond reasonably well, with correlations exceeding 0.7. A common monthly mean climate signal of about 40 W m⁻² is inferred along with local errors of 25 to 30 W m⁻² in most extratropical regions. Except for large scales, there is no useful common signal in the tropics, and reproducibility is especially poor in regions of active convection and where stratocumulus prevails. Although time series of monthly anomalies of surface bulk fluxes from the two models and COADS agree very well over the northern extratropical oceans, the total fields all contain large systematic biases which make them unsuitable for determining ocean heat transports. TOA biases in absorbed shortwave, outgoing longwave and net radiation from both reanalysis models are substantial (>20 W m⁻² in the tropics) and indicate that clouds are a primary source of problems in the model fluxes, both at the surface and the TOA. Time series of monthly COADS surface fluxes are shown to be unreliable south of about 20^∘N where there are fewer than 25 observations per 5^∘ square per month. Only the derived surface fluxes give reasonable implied meridional ocean heat transports. Received: 21 March 2000 / Accepted: 21 June 2000     

A study of the mass,momentum and energy budget of the atmosphere

Production and expenditure rates in the terrestrial budget of various air properties (mass of precipitable water and carbon dioxide, zonal and root mean square momentum, heat, and entropy) are studied. The discussion is based on graphs and diagrams which illustrate the global radiation and heat budget, dynamical energy forms and conversions, hydrologic and carbon dioxide cycles, and meridional cross sections of mass, momentum, heat, and entropy budget terms. A comparison of atmospheric property holdings with expenditure rates results in a fictitious interval of time required to annull the holdings. For momentum, precipitable water, and heat this interval of time has the order of magnitude of 10⁰, 10¹, and 10² days, respectively.

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Zusammenfassung Es werden die Einnahme- und Ausgabeposten beim terrestrischen Haushalt verschiedener Eigenschaften der Luft (Wasserdampf und Kohlensäure als Beispiele von Masseneigenschaften, ferner zonal-vektorieller und skalarer Impuls, Wärme und Entropie) untersucht. Die Diskussion wird durch graphische Darstellungen und Diagramme unterstützt, welche folgende Größen veranschaulichen: den globalen Strahlungs- und Wärmehaushalt, dynamische Energieformen und ihre Umwandlungen, Wasserkreislauf und Kohlensäurekreislauf, sowie Bilanzposten der Massen-, Impuls-, Wärme- und Entropiebilanz in Meridionalschnitten. Eine Vergleichung des Gehalts der Atmosphäre an verschiedenen Eigenschaften mit ihren Verlusten liefert ein fiktives Zeitintervall, in welchem die Reserven aufgebraucht würden, wenn kein Ersatz nachgeliefert würde; die Größenordnung dieses Zeitintervalles ergibt sich zu 10⁰, 10¹ und 10² Tagen für Impuls, Wasserdampf und Wärme.

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Résumé L'auteur étudie la production et la dépense dans le bilan terrestre des différentes propriétés de l'air (la vapeur d'eau et le dioxyde de carbone comme exemples de propriétés de masse, puis la quantité de mouvement zonale-vectorielle et scalaire, la chaleur et l'entropie). Des graphiques illustrent la discussion qui représentent les grandeurs suivantes: économie globale de la radiation et de la chaleur, formes dynamiques de l'énergie et leurs transformations, cycles hydrologique et du dioxyde de carbone, ainsi que les composantes du bilan des masses, de la quantité de mouvement, de la chaleur et de l'entropie en coupes méridionales. La comparaison du contenu des diverses propriétés dans l'atmosphère avec leurs pertes est fournie par un intervalle de temps fictif, pendant lequel les réserves seraient épuisées, au cas où leur renouvellement ferait défaut; l'ordre de grandeur de cet intervalle résulte à 10⁰, 10¹ et 10² jours respectivement pour la quantité de mouvement, la vapeur d'eau et la chaleur.

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With 8 Figures.