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Philip E. Ardanuy and H. Lee Kyle

Abstract

The Earth Radiation Budget experiment, launched aboard the Nimbus-7 polar-orbiting spacecraft in late 1978, has now taken over seven years of measurements. The dataset, which is global in coverage, consists of the individual components of the Earth's radiation budget, including longwave emission, not radiation, and both total and new-infrared albedos. Starting some six months after the 1982 eruption of the El Chichón volcano, substantial long-lived positive shortwave irradiance anomalies were observed by the experiment in both the northern and southern polar regions. Analysis of the morphology of this phenomena indicates that the cause is the global stratospheric aerosol layer which formed from the cloud of volcanic effluents. There was little change in the emitted longwave in the polar regions. At the north pole the largest anomaly was in the near-infrared, but at the south pole the near UV-visible anomaly was larger. Assuming an exponential decay, the time constant for the north polar, near-infrared anomaly was 1.2 years. At mid- and low latitudes the effect of the El Chichón aerosol layer could not be separated from the strong reflected-shortwave and emitted-longwave perturbations issuing from the El Niño/Southern Oscillation event of 1982–83.

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Philip E. Ardanuy and H. Lee Kyle

Abstract

Five years of broad-band earth radiation budget measurements taken by the Nimbus-7 ERB experiment have been archived. This period encompasses the 1982/83 El Niño/Southern Oscillation event, which reached a peak near the beginning of the fifth data year (January 1983). A 41-month outgoing longwave radiation subset of this data set, extending from June 1980 through October 1983, has been further processed to enhance the spatial resolution.

Analysis of the resultant fields and the anomalies from the pre-El Niño climatology provides the first broad-band glimpse of the terrestrial outgoing longwave radiative response to the El Niño event throughout its life cycle. Of particular interest are the quasi-stationary planetary-scale tropical and midlatitude patterns which emerge as the El Niño reaches its peak intensity. Important new implications to the vertical motion field are addressed.

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Phillip A. Arkin and Philip E. Ardanuy

Abstract

Measurement of climatic-scale precipitation (defined here as averages over areas of >104 km2 and periods of five days or longer) is impractical for many areas of the earth without the use of space-based observations. We briefly discuss the history of satellite rainfall estimation schemes and their application to climate studies. Two approaches—direct and indirect—have dominated work until very recently, when attempts to use more integrated techniques began. Indirect schemes, primarily based on visible and infrared (IR) observations of the characteristics of clouds, have been used in the majority of such studies. Direct schemes, such as those that use microwave observations of raindrop-sized hydrometeors, have been limited by a relative lack of the required measurements. A large number of studies have used datasets not originally intended as precipitation estimates at all, such as the NOAA outgoing longwave radiation data, to produce estimates of very large scale rainfall. Current and prospective attempts to overcome some of the difficulties affecting climatic-scale precipitation estimation are described. The Global Precipitation Climatology Project will integrate data from surface obserations, geostationary IR sensors, and polar-orbiting microwave and IR sensors to produce near-global analyses of monthly rainfall. The proposed Tropical Rainfall Measuring Mission will use a single satellite with an instrument package that will make visible, IR, and microwave radiometric observations. The package will also include a precipitation radar. We discuss certain other proposed satellite missions and international programs and their contributions to the production of climatic-scale precipitation estimates. Finally, we propose the development of a global rainfall analysis system.

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Philip E. Ardanuy, H. Lee Kyle, and Hyo-Duck Chang

Abstract

The Nimbus-7 satellite has been in a 955-km, sun-synchronous orbit since October 1978. The Earth Radiation Budget (ERB) experiment has taken approximately 8 years of high-quality data during this time, of which 7 complete years have been archived at the National Space Science Data Center. A final reprocessing of the wide- field-of-view channel dataset is underway. Error analyses indicate a long-term stability of 1% better over the length of the data record.

As part of the validation of the ERB measurements, the archived 7-year Nimbus-7 ERB dataset is examined for the presence and accuracy of interannual variations including the Southern Oscillation signal. Zonal averages of broadband outgoing longwave radiation indicate a terrestrial response of more than 2 years to the oceanic and atmospheric manifestations of the 1982–83 El Niñ/Southern Oscillation (ENSO) event, especially in the tropics. This signal is present in monthly and seasonal averages and is shown here to derive primarily from atmospheric responses to adjustments in the Pacific Ocean. The calibration stability of this dataset thus provides a powerful new tool to examine the physics of the ENSO phenomena.

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Philip E. Ardanuy, H. Lee Kyle, and Douglas Hoyt

Abstract

The analyses of Cess are extended to consider global relationships among the earth's radiation budget (including solar insulation and changes in optically active gass), cloudiness, solar constant, volcanic aerosols, and surface temperature. Interannual variability and correlations between Nimbus-7 THIR/TOMS cloud amount, ERB WFOV longwave, shortwaye, and net radiation, and SAM II aerosol optical depths, along with Hansen and Lebedeff's surface temperature analyses, are assessed.

Solar luminosity is apparently related to the global surface temperature in the 1979–1990 time period based on the Nimbus-7 observations and an extended Hansen and Lebedeff temperature dataset. The 0.40°C range in observed global temperatures may be partitioned into a 0.15°C component due to a 2 W m−2 change in the solar constant and a 0.22°C component due to the increasing concentration of CO2 and other greenhouse gases. A relatively large component of the variance in the global temperature, cloudiness, and radiation budget signals is due to interannual earth system variability over time periods much shorter than a solar cycle (e.g., 2–4 years), for which the solar luminosity experiences no comparable fluctuation.

The Nimbus-7 observations indicate that the global, annual cloud amount varies by +0.3% to −0.5% with a pronounced quasi-biennial periodicity and is inversely proportional to the outgoing longwave flux and surface temperature. The time dependence of aerosols injected into the stratosphere by the explosive 1982 eruption of El Chichón is found to be important, along with the global cloud amount, in describing the time dependence of the earth's albedo during the period.

The sign of the relationship between the earth's surface temperature and the net radiation is of fundamental importance. The Nimbus-7 ERB net radiation observations compared to surface temperature analyses imply a stable climate (at least about some set point that is dictated by other conditions such as the concentration of C02 and other greenhouse gases, that do not apply over the relatively short time interval considered here).

When considering future mission we conclude that reliable and well-characterized satellite datasets with of ideally one to two decades or more are required to perform quantitative analyses of the relationships among different elements of the earth's climate system. To accomplish this, the instruments’ calibration should be maintained and valid to a stability that permits the analysis of interannual global fluctuations at the 0.2% level.

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Philip E. Ardanuy, Larry L. Stowe, Arnold Gruber, Mitchell Weiss, and Craig S. Long

Abstract

Collocated and coincident cloud and outgoing longwave radiation observations taken by experiments on board the Nimbus-7 satellite have been used to infer the daytime longwave cloud-radiative forcing. Through the specification of a time-series of daily values of cloud amount, cloud-top temperature, surface temperature, and outgoing longwave radiation, the clear-sky flux is obtained for both the summer (June, July, and August 1979) and winter (December 1979. January and February 1980) seasons. The longwave component of the cloud-radiative forcing is then computed by subtracting the observed outgoing longwave flux from the inferred clear-sky longwave flux. The results are compared to independent cloud forcing estimates produced using high spatial resolution radiometers and found to agree closely.

The resultant cloud forcing is analyzed regionally, zonally, and globally for each season to quantify, through observation, the role that clouds play in modulating the outgoing longwave radiation. The largest cloud forcing is found over regions of tropical convection, and reaches peak values of about 80 W m−2 in the vicinity of the summer and winter monsoon. Cloud forcing values of less than 10 W m−2 are evident over the deserts the subtropical oceans, and in the polar latitudes, Zonally, the cloud forcing reaches maxima over the Intertropical Convergence Zone (40 to 50 W m−2) and over the polar frontal zones of both hemispheres (25 to 30 W m−2), and minima in the subtropical belts and at the poles. Globally, the cloud forcing is found to be 24 W m−2. The globally averaged cloud cover for the same period is 50%.

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H. Lee Kyle, Philip E. Ardanuy, and Edward J. Hurley

Over six years of data from the earth-radiation-budget (ERB) experiment on board the Nimbus-7 spacecraft have been received to date. Five years of data have been archived and are readily available to the scientific community, while the sixth year's data will be archived by the fall of 1985. There are three complementary, but independent, data sets: earth-radiation-budget data, solar-irradiance data, and shortwave- and longwave-radiance data suitable for bidirectional-reflectance studies. The solar and the wide-field-of-view earth-flux channels are still recording high-quality data, but the narrow-field-of-view scanner failed after 20 months. The condition of the three data sets is described. In addition, plans for data-set improvement are discussed and a simple algorithm to improve the wide-field-of-view data is presented.

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