1.4 TMY3 Data Format The format for the TMY3 data is radically different from the TMY and TMY2 data.. The older TMY data sets used columnar or positional formats, presumably as a method of optimizing data storage space. Such formats are difficult to read, and it is difficult to import specific fields into many software packages. The comma separated value (CSV) format is ubiquitous, and many existing programs and applications provide built-in functions to read or parse it. For that reason, the TMY3 data set is distributed in the CSV format. For compatibility with existing software, NREL has produced an application to convert from TMY3 to TMY2 format. Despite the format differences, the fields in the TMY3 are very similar to those in the TMY2 data set. Fundamental differences are measurement units, which are SI or equivalent in the TMY3, the addition of three new fields for surface albedo and liquid precipitation, and the removal of the fields for present weather, snow-depth, and days since last snowfall that were present in the TMY2. These fields were removed because of incompatible changes in the nature of the source data or because the source data were not available. The TMY3 data files are named according to the USAF site identifier as 999999TY.CSV, where 999999 represents the six digit USAF station identifier (see Appendix A). The TMY3 data format has two file header lines and 8,760 lines of data, each with 68 data fields. The format is documented in Tables 1-1 to 1-3. Table 1-1. TMY3 data header (line 1) Field Element Unit or Description 1 Site identifier code USAF number 2 Station name Quote delimited 3 Station state Two-letter U.S. Postal abbreviation 4 Site time zone Hours from Greenwich, negative west 5 Site latitude Decimal degree 6 Site longitude Decimal degree 7 Site elevation Meter Table 1-2. TMY3 data header (line 2) Field Element 1-68 Data field name and units (abbreviation or mnemonic) 3
Table 1-3. TMY3 data fields (lines 3-8762) Field Element Unit or Range Resolution Description 1 Date MM/DD/YYYY -- Date of data record 2 Time HH:MM -- Time of data record (local standard time) 3 Hourly extraterrestrial radiation on a horizontal surface 4 Hourly extraterrestrial radiation normal to the sun 5 Global horizontal 6 Global horizontal source 7 Global horizontal 8 Direct normal 9 Direct normal source 10 Direct normal 11 Diffuse horizontal 12 Diffuse horizontal source 13 Diffuse horizontal received on a horizontal surface at the top of the atmosphere during the 60-minute period ending at the received on a surface normal to the sun at the top of the atmosphere during the 60-1 Wh/m 2 Total amount of direct and diffuse solar radiation received on a horizontal surface during the 60-minute period ending at the NSRDB User s Manual (Wilcox, 2007b) (modeled) received in a collimated beam on a surface normal to the sun during the 60-1-2 -- See table 1-4 NSRDB User s Manual (Wilcox, 2007b) received from the sky (excluding the solar disk) on a horizontal surface during the 60-minute period ending at the NSRDB User s Manual (Wilcox, 2007b) 4
14 Global horizontal 15 Global horizontal source 16 Global horizontal 17 Direct normal 18 Direct normal source 19 Direct normal 20 Diffuse horizontal 21 Diffuse horizontal source 22 Diffuse horizontal 23 Zenith luminance Candela per 24 Zenith luminance source 25 Zenith luminance Lux 100 lx Average total amount of direct and diffuse received on a horizontal surface during the 60-minute period ending at the Lux 100 lx Average amount of direct normal received within a 5.7 field of view centered on the sun during 60- Lux 100 lx Average amount of received from the sky (excluding the solar disk) on a horizontal surface during the 60-minute period ending at the 10 cd/m 2 Average amount of luminance at the sky's zenith during the 60-26 Total sky cover Tenths of sky 1 tenth Amount of sky dome covered by clouds or obscuring phenomena at the time 27 Total sky cover 28 Total sky cover 29 Opaque sky cover Tenths of sky 1 tenth Amount of sky dome covered by clouds or obscuring phenomena that prevent observing the sky or higher cloud layers at the time 5
30 Opaque sky cover 31 Opaque sky cover 32 Dry-bulb temperature Degree C 0.1 Dry-bulb temperature at the time 33 Dry-bulb temperature 34 Dry-bulb temperature 35 Dew-point temperature Degree C 0.1 Dew-point temperature at the time 36 Dew-point temperature 37 Dew-point temperature 38 Relative humidity Percent 1% Relative humidity at the time 39 Relative humidity 40 Relative humidity 41 Station pressure Millibar 1 mbar Station pressure at the time 42 Station pressure 43 Station pressure 44 Wind direction Degrees from north (360 = 10 Wind direction at the time north; 0 = undefined, calm) 45 Wind direction 46 Wind direction 47 Wind speed Meter/second 0.1 m/s Wind speed at the time 48 Wind speed 49 Wind speed 50 Horizontal visibility Meter* 1 m Distance to discernable remote objects at the time (7777 = unlimited) 51 Horizontal visibility 52 Horizontal visibility 6
53 Ceiling height Meter* 1 m Height of the cloud base above local terrain (77777 = unlimited) 54 Ceiling height 55 Ceiling height 56 Precipitable water Centimeter 0.1 cm The total precipitable water contained in a column of unit cross section extending from the earth's surface to the top of the atmosphere 57 Precipitable water 58 Precipitable water 59 Aerosol optical depth, broadband [unitless] 0.001 The broadband aerosol optical depth per unit of air mass due to extinction by the aerosol 60 Aerosol optical depth, broadband 61 Aerosol optical depth, broadband component of the atmosphere 62 Albedo [unitless] 0.01 The ratio of reflected solar to global horizontal 63 Albedo 64 Albedo 65 Liquid precipitation depth 66 Liquid precipitation quantity 67 Liquid precipitation depth 68 Liquid precipitation depth *Value of -9900 indicates the measurement is missing. Millimeter* 1 mm The amount of liquid precipitation observed at the time for the period in the liquid precipitation quantity field Hour* 1 hr The period of accumulation for the liquid precipitation depth field 7
Flag Table 1-4. Solar radiation and source s Definition 1 Data modeled using METSTAT or from 1961-1990 NSRDB solar fields 2 Data modeled using SUNY Satellite model (time shifted) Flag A B C D E F Table 1-5. Meteorological source s Definition Data as received from NCDC, converted to SI units Linearly interpolated Non-linearly interpolated to fill data gaps from 6 to 47 hours in length Not used Modeled or estimated, except: precipitable water, calculated from radiosonde data; dew point temperature calculated from dry bulb temperature and relative humidity; and relative humidity calculated from dry bulb temperature and dew point temperature Precipitable water, calculated from surface vapor pressure; aerosol optical depth, estimated from geographic correlation? Source does not fit any of the above. Used mostly for missing data Flag Table 1-6. Meteorological s Definition 1 6 Not used 7 Uncertainty consistent with NWS practices and the instrument or observation used to obtain the data 8 Greater than 7 because values were interpolated or estimated 9 Greater than 8 or unknown 0 Not definable 8