Abstract:
The major parameters making up this data file are sunrise/sunset (local standard time), extraterrestrial radiation, direct radiation, global radiation on a horizontal surface (1. observed data, 2. engineering corrected data, 3. model corrected data), supplemental radiation measurement, minutes and percent of possible sunshine, temperature (max, min, mean), precipitation, snowfall, snow depth, days
... with weather, and sky cover. Daily solar radiation - surface meteorological data (SOLDAY) is a common format designed to provide quality controlled daily solar insolation and collateral meteorological data available at the National Climatic Data Center (NCDC). SOLDAY data is the second phase of the rehabilitation process satisfying a need for long-term insolation data. Phase one created the SOLMET hourly solar radiation file (DSI-9724, C00045). It consists of hourly long-term insolation data. The daily solar data were reformated by removing all known procedural and instrumental errors and includes all available meteorological elements. Rehabilitated hourly insolation data stations used in SOLMET were not chosen for inclusion in the SOLDAY format because of data redundancy. SOLDAY daily sums include data from stations that: 1. Used mechanical integrators for totals and recorded solar radiation on circular charts. (Most of the SOLDAY stations were selected from this category.) 2. Recorded solar radiation on strip charts and daily amounts calculated by summing hand-computed hourly values (one SOLDAY station - Blue Hill - falls into this category, as does the majority of SOLMET stations.) 3. Recorded solar radiation on strip charts and daily amounts obtained for a part of the time by summing hand-computed hourly values. For the remainder of the time, daily sums were obtained from a mechanical integrator. The related data files include DSI-9724 SOLMET Hourly Solar Radiation (C00047), DSI-9734 Typical Meteorological Year (C00045) and DSI-3211 Summary of the Day First Order (C00359). The surface meteorological data are a metric (SI) conversion of the summary of daily surface observations contained in NCDC's DSI-9750. The identification portion of the file format contains the file number, station number and date of the daily observation. The local standard time (LST) of sunrise and sunset may be considered also as identification. The rate change in sunrise/sunset times contains 1-minute irregularities due to rounding of LST time of sunrise/sunset. A list of stations showing latitude, longitude, elevation, periods of record and changes in station location are available in the SOLDAY user's manual DSI-9739. The solar radiation portion of the file format provides for: 1.The theoretical extraterrestrial radiation on a horizonal surface based on a solar constant of 1377 J/(M2*S). 2. Direct radiation. 3. Three fields of global radiation - observed data, observed data corrected for engineering changes (such as recorder scales, sensor deterioration, calibration errors), and observed data corrected to a standard year irradiance model. 4. A supplemental radiation field. 5. Minutes and percentage of possible sunshine. Individual station histories note pertinent information making it possible to properly interpret the data. If the data were not observed or more than 60 days elapsed between clear solar non irradiance values, no sky cover/sunshine model will be used to fill the data gaps. 
