On the closure relationship among shortwave radiometric measurements under a cold climate during winter

To support the Baseline Surface Radiation Network initiative, a new radiometric station was set up in Qiqihar, China, which has a monsoon-influenced hot-summer humid continental climate (Dwa) under the Köppen–Geiger climate classification, which is extremely rare in the world. Through a two-month operation in winter, it was observed that the station suffered from some nonclosure problems that impacted the quality of its measurements—the summation of the beam and diffuse components do not agree well with the global one. This work therefore investigates the possible causes of the problems and presents a set of quality checks to identify the causes. It is found that the problems originate from the mis-leveling of the sun tracker and frost deposition on the pyrheliometer, and once they are fixed, the closure relationship is maintained.