Development and evaluation of a snow accumulation countermeasure for ground-based microwave radiometers for atmospheric and cloud observations in heavy snowfall areas

Abstract

Continuous observations of the atmosphere and clouds are essential for understanding snowfall processes. While ground-based microwave radiometers (MWRs) are effective tools, their accuracy degrades when liquid water or snow accumulates on the radome. Standard built-in blowers often fail to prevent snow accumulation in heavy snowfall regions. To address this, we implemented a high-capacity external blower as a snow accumulation countermeasure. Precipitable water vapor (PWV) was observed in Nagaoka, Niigata, from November 2024 to March 2025 using two identical compact MWRs: one with the external blower (BL) and one without it (NOBL). PWV was retrieved using a machine-learning model and evaluated against the Japan Meteorological Agency Local Analysis (LA) data. Under snow-free conditions, both units exhibited high consistency (mean error [ME] = 0.14 mm, root mean square error [RMSE] = 1.04 mm), indicating that both can be utilized to verify the effectiveness of snow accumulation countermeasures. During snowfall events, the accuracy of the NOBL unit significantly decreased (RMSE = 2.51 mm) due to snow accumulation and subsequent meltwater film formation on the radome. In contrast, the BL unit maintained accuracy comparable to non-snow conditions (RMSE = 1.68 mm). Furthermore, data availability during snowfall reached 99.9% for the BL unit, compared to only 67.8% for the NOBL unit. These results demonstrate that the external blower system is highly effective for maintaining the reliability and continuity of MWR observations in heavy snowfall areas, marking a significant technical advancement for establishing observation networks in such challenging environments.