Ann T. Mecherikunnel

Data on total and spectral solar irradiance.

This paper presents a brief survey of the data available on solar constant and extraterrestrial solar spectral irradiance. The spectral distribution of solar radiation at ground surface, computed from extraterrestrial solar spectral irradiance for several air mass values and for four levels of atmospheric pollution, is also presented. The total irradiance at ground level is obtained by integration of the area under the spectral irradiance curves. It is significant that, as air mass increases or as turbidity increases, the amount of energy in the infrared relative to the total increases and that the energy in the UV and visible decreases.

Total and spectral solar irradiance measured at ground surface

This paper presents the results of a series of total and spectral solar irradiance measurements made at ground surface (Table Mountain Facility, Calif., altitude 2.18 km). The spectral irradiance data are presented for the 0.3-3.0-microm spectral region for air mass 1.5.

A comparison of solar total irradiance observations from spacecraft: 1985-1992

This paper presents a statistical comparison of the solar total irradiance measured from the Nimbus-7, the Solar Maximum Mission (SMM), the Earth Radiation Budget Satellite (ERBS), and the Upper Atmosphere Research Satellite (UARS) spacecraft platforms, for the period 1985 –1992. The mean irradiance, standard deviation, and the correlation among the daily irradiance remained high during periods of high solar activity. Linear regression models are established to estimate the irradiance measurements from one platform by the others. The results are consistent with the observations. However, the Nimbus-7 ERB responses show a drift during 1989–1992. The absolute irradiance observed by each instrument varies within the uncertainty associated with the corresponding radiometer.

Earth Radiation Budget Satellite extraterrestrial solar constant measurements - 1986-1987 increasing trend

Abstract From June 1986 through Nov 1987, the Earth Radiation Budget Satellite (ERBS) pyrheliometric measurements indicated that the solar constant was increasing approximately +0.02% per year. Earlier ERBS measurements indicated that the solar constant was declining approximately −0.03% per year during the 1984 through mid-1986 period. Since mid-1986 represents the beginning of solar cycle 22, it is believed that the reversal in the long-term solar constant trend may be linked to increased solar activity which is associated with the beginning of the 11-year sunspot cycle. The typical value of the solar constant was found to be 1365 Wm-2.

Solar Total Irradiance: A Reference Value for Solar Minimum

Simultaneous solar total irradiance observations performed by absolute radiometers on board satellites during the quiet-Sun period between solar cycles 21 and 22 (1985–1987), are analyzed to determine the solar total irradiance at 1 AU for the solar minimum. During the quiet-Sun period the total solar irradiance, UV irradiance, and the various solar activity indices show very little fluctuation. However, the absolute value of the solar total irradiance derived from the observations differ within the accuracy of the radiometers used in the measurements. Therefore, the question often arises about a reference value of the solar total irradiance for use in climate models and for computation of geophysical, and atmospheric parameters. This research is conducted as a part of the Solar Electromagnetic Radiation Study for Solar Cycle 22 (SOLERS22). On the basis of the study we recommended a reference value of 1367.0 ± 0.04 W m-2 for the solar total irradiance at 1 AU for a truly quiet Sun. We also find that the total solar irradiance data for the quiet-Sun period reveals strong short-term irradiance variations.

Solar total irradiance observations from spacecraft: 1992–1993

A brief review of the simultaneous observations of solar total irradiance performed by the UARS ACRIM II (upper atmosphere research satellite active cavity radiometer irradiance monitor), EURECA SOVA 1 and SOVA 2 (European retrievable carrier platform solar variability experiments), ERBS ERBE (Earth Radiation Budget Satellite Earth Radiation Budget Experiment), Nimbus 7 ERB, and Atlas 1 and 2 in 1992–1993 (a period characterized as the declining phase of solar cycle 22), is presented in this paper. Statistical comparison of the irradiance values and the linear relationships among the time series are examined for the overlap period August 1992 to May 1993. The mean irradiance at 1 astronomical unit (AU) observed by the UARS ACRIM II, EURECA SOVA 1, EURECA SOVA 2, and ERBS ERBE is within the range of 1365.5–1366.9 W m−2, and high correlation (r2 = 0.94) exists among the time series. Linear regression models based on the measurements are used in estimating the observed irradiance and predicting the missing values. The challenge in establishing a homogeneous long-term database from the independent observations of shorter duration requires a clear understanding of the compatibility of the data sets and any instrument-related drift or degradation.

Data on total and spectral solar irradiance: reply to comments

The letter is a response to Frohlichs (1983) comments on an earlier paper (Mecherikunnel et al., 1983) containing a brief survey of the available data on the solar constant and its spectral distribution. The sources of the initial data used in the above study are mentioned, and comments are made on the accuracy of the measurements. Reasons are given for using NASA/ASTM data in the computations.

The Estimation of Emitted and Reflected Energy over the Central Pacific Using Meteorological Parameters

The authors conducted a quantitative investigation of the relationship between meteorological parameters (chiefly cloud cover) and the principal components of the earths radiation budget. The area of study is the tropical central Pacific, where considerable variation in cloudiness and flux was observed from 1985 to 1989. The observed variations were in response to the El Nino-Southern Oscillation event of 1987. International Satellite Cloud Climatology Project (ISCCP) C2 parameters were used as independent variables in the development of multiple linear models to predict Earth Radiation Budget Experiment (ERBE) outgoing longwave radiation (OLR) and shortwave (SW) fluxes. Net radiation estimates were obtained from OLR and SW predicted fluxes. The technique of all-subsets regression was used to determine which combination of ISCCP C2 parameters could best predict OLR and SW fluxes. The models were developed for the years 1985 and 1989 (non-ENSO years) and tested by both month and year on the years 1986 through 1988. Predicted fluxes were obtained for three 15° latitude zones, north (7.5° to 22.5°N), central (7.5°S to 7.5°N), and south (7.5°S to 22.5°S). Over the 60 months of data, explained variances (R 2 ) of over 90% for the development and test periods were typical. An increase in the accuracy of the OLR models was observed when noncloud variables were included. This accuracy improvement was most apparent when cloud amounts were either very low or very high and homogeneous. Biases (predicted-observed) were all less than 4 Wm −2 and rms estimates were within the range of uncertainty for ERBE monthly mean flux estimates. Flux estimates based on linear models could serve as a means of extending long-term radiation balance datasets during intervals of time with limited satellite coverage

Calibration of EOS multispectral imaging sensors and solar irradiance variability

Earth Observation System (EOS) optical multispectral imaging sensors provide images of the earth at various spectral and spatial resolutions, in the visible (VIS) and infrared (IR) regions of the solar spectrum. Accurate knowledge of extraterrestrial solar spectral irradiance and its variations with time, are needed to trace sensor calibration in space, and for the development of terrestrial atmospheric models needed in data validation. A brief review of the extraterrestrial solar VIS/IR spectral irradiance available in the literature will be reviewed, and the need to develop an extraterrestrial solar spectral irradiance for the EOS studies will be pointed out. The solar calibration of the Earth Radiation Budget Experiment (ERBE), earth-viewing sensors will be discussed. Observed variations in the solar constant (solar irradiance, at the mean sun-earth distance of one astronomical unit, integrated over all wavelengths), and solar spectral irradiance with solar activity and its implications for EOS studies also will be discussed.