Clear-Sky Shortwave Downward Flux at the Earth's Surface: Ground-Based Data vs. Satellite-Based Data

The radiative flux data and other meteorological data in the BSRN archive start from 1992, but the RadFlux data, the clear-sky radiative fluxes at the BSRN sites derived through regression analyses of actually observed clear-sky fluxes, did not come into existence until the early 2000s, and at first, they were limited to the 7 NOAA SURFRAD and 4 DOE ARM sites, a subset of the BSRN sites. Recently, the RadFlux algorithm was applied more extensively to the BSRN sites for the production of clear-sky ground-based fluxes. At the time of this writing, there are 7119 site-months of clear-sky fluxes at 42 BSRN sites spanning the time from 1992 to late 2017. These data provide an unprecedented opportunity to validate the satellite-based clear-sky fluxes. In this paper, the GEWEX SRB GSW(V3.0) shortwave downward fluxes spanning 24.5 years from 1983-07 to 2007-12, the CERES SYN1deg(Ed4A) and EBAF(Ed4.0) shortwave fluxes spanning 2000-03 to mid-2017 are compared with their RadFlux counterparts on the hourly, 3-hourly, daily and monthly time scales. All the three datasets show reasonable agreement with their ground-based counterparts. Comparison of the satellite-based surface shortwave clear-sky radiative fluxes to the BSRN RadFlux analysis shows negative biases. Further analysis shows that the satellite-based atmosphere contains greater aerosol optical paths as well as more precipitable water than RadFlux analysis estimates.

The cloud-free global energy balance and inferred cloud radiative effects: an assessment based on direct observations and climate models

In recent studies we quantified the global mean Earth energy balance based on direct observations from surface and space. Here we infer complementary reference estimates for its components specifically under cloud-free conditions. While the clear-sky fluxes at the top of atmosphere (TOA) are accurately known from satellite measurements, the corresponding fluxes at the Earth's surface are not equally well established, as they cannot be directly measured from space. This is also evident in 38 global climate models from CMIP5, which are shown to greatly vary in their clear-sky surface radiation budgets. To better constrain the latter, we established new clear-sky reference climatologies of surface downward shortwave and longwave radiative fluxes from worldwide distributed Baseline Surface Radiation Network sites. 33 out of the 38 CMIP5 models overestimate the clear-sky downward shortwave reference climatologies, whereas both substantial overestimations and underestimations are found in the longwave counterparts in some of the models. From the bias structure of the CMIP5 models we infer best estimates for the global mean surface downward clear-sky shortwave and longwave radiation, at 247 and 314 Wm^-2, respectively. With a global mean surface albedo of 13.5% and net shortwave clear-sky flux of 287 Wm^-2 at the TOA this results in a global mean clear-sky surface and atmospheric shortwave absorption of 214 and 73 Wm^-2, respectively. From the newly-established diagrams of the global energy balance under clear-sky and all-sky conditions, we quantify the cloud radiative effects not only at the TOA, but also within the atmosphere and at the surface.

Two methods for retrieving UV index for all cloud conditions from sky imager products or total SW radiation measurements

Cloud effects on UV Index (UVI) and total solar radiation (TR) as a function of cloud cover and sunny conditions (from sky images) as well as of solar zenith angle (SZA) are assessed. These analyses are undertaken for a southern-hemisphere mid-latitude site where a 10-years dataset is available. It is confirmed that clouds reduce TR more than UV, in particular for obscured Sun conditions, low cloud fraction (<60%) and large SZA (>60°). Similarly, local short-time enhancement effects are stronger for TR than for UV, mainly for visible Sun conditions, large cloud fraction and large SZA. Two methods to estimate UVI are developed: (1) from sky imaging cloud cover and sunny conditions, and (2) from TR measurements. Both methods may be used in practical applications, although Method 2 shows overall the best performance, as TR allows considering cloud optical properties. The mean absolute (relative) differences of Method 2 estimations with respect to measured values are 0.17 UVI units (6.7%, for 1 min data) and 0.79 Standard Erythemal Dose (SED) units (3.9%, for daily integrations). Method 1 shows less accurate results but it is still suitable to estimate UVI: mean absolute differences are 0.37 UVI units (15%) and 1.6 SED (8.0%).

THE EFFECTS OF ADRENALECTOMY AND HYPOPHYSECTOMY UPON EXPERIMENTAL DIABETES IN THE CAT

1. The hypophysectomized cat shows an alleviation of the diabetes following pancreatectomy comparable to that previously demonstrated by others in the dog. 2. It is possible by various procedures to remove both adrenals and all the pancreas from cats. Such animals have survived for as long as 4 weeks without the use of insulin, the average survival being 18 days. Daily injections of cortical extract are necessary. By contrast, cats deprived of insulin by similar procedures but with adrenals intact survive only 4–5 days. 3. Adrenalectomized-depancreatized cats show as striking an alleviation of the diabetes as do those hypophysectomized and depancreatized. This is expressed by the markedly decreased glucose, nitrogen and acetone body excretion compared to that found in the depancreatized cat, as well as by the increased survival period. 4. Removal of epinephrine by denervation or demedullation of the adrenals does not protect against pancreatic diabetes in the cat. 5. The carbohydrate tolerance of depancreatized cats is not significantly increased by hypophysectomy or adrenalectomy. The exceptions to this finding have all been in animals presenting varying degrees of spontaneous hypoglycemia. 6. It is our opinion that the effects of hypophysectomy or adrenalectomy upon pancreatic diabetes are due to diminution of the production of glucose and acetone bodies rather than to the resumption of normal carbohydrate utilization.

BIOCHEMICAL STUDIES ON SHOCK : I. THE METABOLISM OF AMINO ACIDS AND CARBOHYDRATE DURING HEMORRHAGIC SHOCK IN THE RAT

During and following the production of shock by hemorrhage in the normal, suprareno-demedullated, and suprarenalectomized rat, the following significant changes in amino acid and carbohydrate metabolism have been observed. 1. In the intact, suprareno-demedullated, and suprarenalectomized rat there is a progressive rise in the whole blood and plasma amino acid nitrogen levels during and after a fatal, shock-inducing hemorrhage. The rate of rise varies inversely with the survival time. In animals surviving the hemorrhage there is little or no elevation in whole blood amino acid levels during the 8 hours following hemorrhage, and a decrease in 24 hours due to hemodilution. The plasma amino acids, however, rise slightly. 2. The blood amino acid nitrogen elevation occurs only after the blood pressure has fallen to between 85 and 90 mm. of Hg. 3. The blood keto acids, as pyruvate, and the blood lactate become elevated during shock in the normal, suprareno-demedullated and suprarenalectomized rat. 4. In the normal fasted rat with low liver glycogen stores the blood sugar may rise moderately or may not rise at all during hemorrhagic shock. In animals with high liver glycogen levels (fed rats or fasted rats previously fed high protein diets) shock generally induces a marked hyperglycemia. In both groups hypoglycemia may occur terminally. 5. In the suprareno-demedullated and suprarenalectomized rats shock is always accompanied by a fall in the blood sugar. 6. There is no significant difference between the liver glycogen levels of suprareno-demedullated rats fasted 48 hours and those similarly fasted but surviving 24 hours after a hemorrhage. The blood chemical changes have been interpreted as due to a decrease in hepatic function resulting from early anoxia of the liver and to the later effects of anoxia on the peripheral tissues causing an increased rate of protein breakdown and of glucose utilization and an accumulation of lactate and pyruvate in the blood and tissues.

BIOCHEMICAL STUDIES ON SHOCK : II. THE ROLE OF THE PERIPHERAL TISSUES IN THE METABOLISM OF PROTEIN AND CARBOHYDRATE DURING HEMORRHAGIC SHOCK IN THE RAT

The changes in the blood levels of amino nitrogen, glucose, lactate, and pyruvate were compared in eviscerate (liverless) rats and eviscerate rats subjected to hemorrhage, in order to establish the rôle of the peripheral tissues in the blood changes during shock. It was found that:- 1. The blood amino acids accumulate at a more rapid rate in the bled liverless rats than in the control liverless animals. 2. The blood sugar falls more rapidly in the liverless rat after hemorrhage, both in animals with intact suprarenal glands and those with enucleated suprarenal medullae. 3. The blood lactate and pyruvate rise slowly in the liverless rat, but maintain a constant relation to each other except terminally when convulsions occur. In the bled liverless rat both lactate and pyruvate increase much more rapidly than in the control liverless rat, and the lactate/pyruvate ratio also increases. These data are interpreted to indicate that a decrease in liver function during hemorrhagic shock serves to make apparent a considerable increase in peripheral protein catabolism and accentuates the effects of an increased carbohydrate utilization by the periphery. The lactate and pyruvate changes are determined chiefly by anoxia of the peripheral tissue and probably indicate an increasing predominance of anaerobic over aerobic metabolism of carbohydrate in muscle. The liver plays a negligible rôle in the lactate and pyruvate changes in shock.

BIOCHEMICAL STUDIES ON SHOCK : III. THE ROLE OF THE LIVER AND THE HEPATIC CIRCULATION IN THE METABOLIC CHANGES DURING HEMORRHAGIC SHOCK IN THE RAT AND THE CAT

1. In a series of rats subjected to hemorrhage and shock a high negative correlation was found between the portal and peripheral venous oxygen saturations and the arterial blood pressure on the one hand, and the blood amino nitrogen levels on the other, and a high positive correlation between the portal and the peripheral oxygen saturations and between each of these and the blood pressure. 2. In five cats subjected to hemorrhage and shock the rise in plasma amino nitrogen and the fall in peripheral and portal venous oxygen saturations were confirmed. Further it was shown that the hepatic vein oxygen saturation falls early in shock while the arterial oxygen saturation showed no alteration except terminally, when it may fall also. 3. Ligation of the hepatic artery in rats did not affect the liver's ability to deaminate amino acids. Hemorrhage in a series of hepatic artery ligated rats did not produce any greater rise in the blood amino nitrogen than a similar hemorrhage in normal rats. The hepatic artery probably cannot compensate to any degree for the decrease in portal blood flow in shock. 4. An operation was devised whereby the viscera and portal circulation of the rat were eliminated and the liver maintained only on its arterial circulation. The ability of such a liver to metabolize amino acids was found to be less than either the normal or the hepatic artery ligated liver and to have very little reserve. 5. On complete occlusion of the circulation to the rat liver this organ was found to resist anoxia up to 45 minutes. With further anoxia irreversible damage to this organ's ability to handle amino acids occurred. 6. It is concluded that the blood amino nitrogen rise during shock results from an increased breakdown of protein in the peripheral tissues, the products of which accumulate either because they do not circulate through the liver at a sufficiently rapid rate or because with continued anoxia intrinsic damage may occur to the hepatic parenchyma so that it cannot dispose of amino acids.

BIOCHEMICAL STUDIES ON SHOCK : IV. THE OXYGEN CONSUMPTION OF LIVER AND KIDNEY TISSUE FROM RATS IN HEMORRHAGIC SHOCK

1. With increasing severity of shock following hemorrhage in fasted rats there is an increasing depression in the rate of oxygen uptake, in oxygen, of liver slices from the bled animals. The respiration of kidney tissue is only slightly depressed even in severe states of shock. 2. The rates of oxygen uptake of liver tissue from bled rats are nicely correlated with the increases in blood amino nitrogen that follow severe hemorrhage. 3. A supplement of coenzyme factors, in the form of a hot water extract of normal rat liver, increases the oxygen uptake of liver tissue from rats in mild shock, but is without effect on the respiration of liver slices from rats in moderate or severe shock. 4. The ability of rat liver to oxidize succinate is not impaired even in severe shock, but the extra oxygen uptake does not improve the basal rate of respiration of the tissue. 5. Effects on the rate of oxygen uptake of normal rat liver slices comparable to those seen after hemorrhage could be produced by exposing the tissue to an atmosphere of nitrogen for periods of 15 and 60 minutes. This treatment had more marked effects on the respiration of kidney slices than are found after hemorrhage, but the kidney, unlike the liver, exhibited a marked degree of recovery in the presence of glucose. 6. The significance of these findings is briefly discussed.

Impact of Island-Induced Clouds on Surface Measurements: Analysis of the ARM Nauru Island Effect Study Data

An Atmospheric Radiation and Cloud Station (ARCS) was established on the island of Nauru by the Atmospheric Radiation Measurement (ARM) Program. Analysis of the Nauru99 field experiment data indicated that measurements at the ARCS were affected by a cloud plume that was induced by diurnal heating of the island. During the Nauru Island Effects Study, instrumentation was installed at a second site to develop criteria for identifying when the cloud plume occurs and to quantify its effect on ARCS measurements. The plume directional heading and frequency of occurrence are affected by the large-scale tropical circulation. During the present study, in which an El Niño was developing, Nauru was in a region of active convection, and easterly trade winds were not dominant; plumes were observed in 25% of satellite images, and only one-half of the observed plumes were downwind of the ARCS site. Surface wind direction, surface air temperature, and downwelling solar radiation at the two sites were used to identify periods when the cloud plume affected surface measurements. Differences in low-cloud frequency and surface radiation between plume-affected and non-plume-affected periods were examined. Existence of the cloud plume increased the average low-cloud frequency of occurrence from 20% to 35%, decreased the average downwelling shortwave radiation by 50–60 W m−2, and increased the average downwelling longwave radiation by 5–10 W m−2. Installing a suite of surface meteorological instruments and a global shortwave radiometer at a second site will allow for the long-term quantification of the cloud plume effect on the radiation field at the ARCS site.

From Dimming to Brightening: Decadal Changes in Solar Radiation at Earth's Surface

Variations in solar radiation incident at Earth's surface profoundly affect the human and terrestrial environment. A decline in solar radiation at land surfaces has become apparent in many observational records up to 1990, a phenomenon known as global dimming. Newly available surface observations from 1990 to the present, primarily from the Northern Hemisphere, show that the dimming did not persist into the 1990s. Instead, a widespread brightening has been observed since the late 1980s. This reversal is reconcilable with changes in cloudiness and atmospheric transmission and may substantially affect surface climate, the hydrological cycle, glaciers, and ecosystems.

Cloud Sky Cover versus Cloud Fraction: Whole-Sky Simulations and Observations

The relationship between hemispherical sky cover and nadir-view cloud fraction is examined by using both model simulations and surface observations. Monte Carlo simulations of ground-based hemispherical measurements are based on four-dimensional cloud fields produced by a large-eddy simulation model. Surface hemispherical observations are performed during the Atmospheric Radiation Measurement Program’s Cloudiness Intercomparison Intensive Operational Period. It is shown that (i) 15-min averages of frequently sampled (30 s) sky cover provide a reasonable estimation of the cloud fraction for limited fields of view and that (ii) this estimation can be substantially improved (for cumulus clouds) if additional information about the cloud aspect ratio is incorporated into the retrieval process.

Absorption of Solar Radiation by Clouds: Observations Versus Models

There has been a long history of unexplained anomalous absorption of solar radiation by clouds. Collocated satellite and surface measurements of solar radiation at five geographically diverse locations showed significant solar absorption by clouds, resulting in about 25 watts per square meter more global-mean absorption by the cloudy atmosphere than predicted by theoretical models. It has often been suggested that tropospheric aerosols could increase cloud absorption. But these aerosols are temporally and spatially heterogeneous, whereas the observed cloud absorption is remarkably invariant with respect to season and location. Although its physical cause is unknown, enhanced cloud absorption substantially alters our understanding of the atmosphere's energy budget.

Renal gluconeogenesis in eviscerated diabetic rats

Experiments were carried out in eviscerated rats having intact kidneys to examine the effects on body glucose of some conditions known to stimulate overall gluconeogenesis. Preliminary experiments confirmed the enhancing effect of renal ligation on falling blood glucose concentration after evisceration. Adrenodemedullation of alloxan-diabetic rats did not affect blood glucose concentration, but comparison with completely adrenalectomized rats again supported previous conclusions that the adrenocortical hormones, in the presence of the kidneys, maintained the blood glucose at higher concentrations after evisceration. Calculated changes in total body glucose concentration over a 4-hr period after evisceration of several groups of alloxan-diabetic rats with intact kidneys showed that epinephrine, like cortisol, consistently reduced losses of total body glucose compared to the controls. An intravenous infusion of lactic acid so diminished the fall in total body glucose in diabetic rats that changes actually became positive, which indicated a net addition of glucose to the body fluids. Thus, the increased rate of disappearance of blood glucose that follows renal ligation in eviscerated animals results in large part from the interruption of renal gluconeogenesis, and the kidneys as well as the liver must be taken into account when considering the total glucogenic capacity of the body.