| INSTRUMENT MENTOR MONTHLY SUMMARY REPORT | |
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IMMSNo 3707 loaded
| Source: SKYRAD |
Report Date: 03/2010 |
Summary Originator: Tom Stoffel
Instrument Mentor Monthly Summary Report for SKYRAD: 03/2010
1. Data Review:
DATA INTEGRITY:
Downwelling broadband solar and atmospheric irradiances (SKYRAD) data for March 2010 were excellent with nearly 100% data collection at all stations (NSA, and TWP). Of the 1-minute irradiance data collected, over 99% of the shortwave and 100% of the longwave data passed automated data quality tests.
The ARM Mobile Facility (AMF) SKYRAD/GNDRAD instruments at Azores (HFE) – commenced data collection April 2009. There are no automated statistics for this station. Please see notable anomalies for details.
NOTABLE ANOMALIES (all times are GMT):
Certain sites may have additional isolated problems that were not considered notable or just missed in this document and have not been mentioned.
NSA
NSA/Barrow(C1)/SKYRAD – Longwave and shortwave data for March appears good. Brief instrument shading apparent starting early April 1630-1700GMT. No DQR currently covers this shading issue.
NSA/Atqasuk(C2)/SKYRAD . Longwave and Shortwave data for March appears good. Tracker appears to have had start problems 3/20-3/22. Some NIP frost reported various times through March. See D100401.1 for details
AMF
Official start May 1st 2009.
GRW/SKYRAD – Data acceptable for March except for met tower obstruction approx. 1800GMT during clear days. See D090831.1 for details.
RHUBC-II Cerro Toco
Deployed starting 16 July-7 Aug 2009. No Quickplots or Archive data available for this datastream.
TWP
TWP/Manus(C1)/SKYRAD – March data appears good.
TWP/Nauru(C2)/SKYRAD – March data is typical for this site. Derived – downwelling shortwave irradiance nears -200 W/m2 during cloud/shade conditions typical of this site. Up to -40 and -50 W/m2 can be still acceptable for these instruments and is likely due to the persistent cloud forcing conditions at this site. March 1 may have had an unidentified brief tracker failure near solar noon.
TWP/Darwin(C3)/SKYRAD – March data appears good.
RADIOMETER DEPLOYMENT NOTES:
Detailed information about the radiometer deployment locations, calibration factors, etc. is available from the ARM Instrument Management (AIM) System – http://www.nrel.gov/aim.
2. Instrument Performance Issues and Trends:Due to inherent radiometer measurement performance characteristics, the best estimate for hemispheric Downwelling Shortwave (DS) is the sum of the Direct Normal Irradiance (DNI) and the Downwelling Diffuse (DD): DS = DNI * Cosine (Solar Zenith angle) + DD. Continued small discrepancies and intermittent data inconsistencies among coincident measurements of 1-minute averaged DS, DNI, and DD broadband irradiances continue (approximately 20 to 50 Watts per square meter). Clear-sky discrepancies are generally limited to early morning and late afternoon when the solar zenith angle is greater than 80 degrees. DS is generally less than the combined DNI and DD for a specific solar zenith angle. Similar discrepancies occur during partly cloudy conditions during any daylight period. The sources of these apparent discrepancies can be attributed to radiometer measurement characteristics: Angular Response – Pyranometer and pyrheliometer calibration responsivities vary with solar zenith angle Rs(Z); Time Constant – Thermopile-based radiometers have time response characteristics dependent on sensor size and other design factors; and, Thermal offset errors - Effects of infrared (sky) radiation and other environmental factors effecting the heat exchange within the radiometer different from the conditions present during calibration will effect an irradiance measurement. Each of these instrument issues have been included in the estimated measurement uncertainties and continue to be subjects of further study. All DS and DD measurements are based on pyranometer calibration results for solar zentith angle of 45 degrees [Rs(45)]. All ARM calibrations provide a full angular characterization of pyranometer responsivity, Rs(Z) for clear sky conditions. Applying the known pyranometer responsivity as a function of solar zenith angle [Rs(Z)] can improve the agreement with summed DNI and DD. The two models of pyranometer used for DS and DD cannot respond equally to rapidly changing sky conditions. The time response for the DS pyranometer Model PSP is 1 sec (1/e) and 5 sec for the DD pyranometer Model 8-48. The pyrheliometer Model NIP has a 1 sec time response. The DD pyranometer was selected for its low thermal offset characteristics. Lastly, the thermal characteristics of the two pyranometers (DS and DD) and the pyrheliometer (DNI) remain a subject of study. Day or night, the DS radiometer can produce from -30 W/sq m to +5 W/sq m "offset" in measured irradiance. The DD exhibits offset of less than +/- 3 W/sq m.
3. Current Task Status:See SIRS IMMS
4. Near-Term Plans:See SIRS IMMS
5. Accomplishments:See SIRS IMMS