Investigation of the Downwelling LW Differences Between the Niamey AMF Main and Supplementary Sites

DISCLAIMER This report was prepared as an account of work sponsored by the U.S. Government. Neither the United States nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the U.S. Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the U.S. Government or any agency thereof. Executive Summary The overall average downwelling longwave (LW) measured at the Niamey supplementary facility (S1) is 6-8 Wm-2 less than that measured by the two instruments located at the ARM Mobile Facility (AMF) main (N1) site. Examination of all other data available at both sites does not reveal any overarching differences that suggest this should be the case. However, examination of the pyrgeometer case and dome temperatures do suggest that the S1 values are also anomalously low, which in turn would explain the downwelling LW anomaly since the LW is calculated using these temperatures. Our recommendation then is to normalize the S1 data to the average N1 value by applying an adjustment factor to the S1 downwelling pyrgeometer case and dome temperatures (in Kelvin), then recalculating the downwelling LW values. The adjustment factor (0.00305) has been determined as that factor that brings the overall average S1 LWdn to agree with the overall average of the two N1 LWdn data series. We note that there is no reason to expect that the two site averages would actually be exactly equal to one another, and thus our recommendation is viewed as likely moving the S1 data in the right direction and by normalizing to the N1 average will help facilitate more meaningful temporal variability studies at least. It is also strongly recommended that for all future AMF deployments where supplementary sites will also be deployed, that the supplementary instrument systems (complete) be assembled as they will be operated in the field and run for at least a few days beside the corresponding AMF main site instruments, both at the beginning and end of the AMF field campaign. …