Integrated relative humidity as a layer-resolved indicator for moisture-precipitation interactions.
Moufeng Wan1, Hui Su2, Chengxing Zhai3
1State Key Laboratory of Climate Resilience for Coastal Cities, Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
Scientific Reports
|April 4, 2026
Summary
We developed Integrated Relative Humidity (IRH), a new diagnostic tool, to understand how moisture and rain interact in Hong Kong. This method analyzes different atmospheric layers to predict rainfall events more accurately.
Area of Science:
- Atmospheric Science
- Meteorology
- Climatology
Background:
- Precipitation forecasting in subtropical coastal regions presents challenges due to complex moisture dynamics.
- Understanding layer-specific atmospheric saturation is crucial for improving precipitation prediction models.
Purpose of the Study:
- To introduce and validate Integrated Relative Humidity (IRH), a novel layer-resolved diagnostic for tropospheric saturation.
- To investigate moisture-precipitation interactions across different precipitation lifecycle stages in Hong Kong.
Main Methods:
- Utilized 16 years of radiosonde and rain gauge data (2005-2020) for Hong Kong.
- Classified precipitation into four stages: No Rain (NR), Before Rain (BR), During Rain (DR), and After Rain (AR).
- Computed IRH from surface to 150 hPa, analyzing probability density functions (PDFs) and reversed cumulative distribution functions (RCDFs) for each stage.
Main Results:
- IRH PDFs revealed distinct vertical saturation structures for each precipitation stage, with peaks near 850 hPa.
- Deep-column saturation was highest During Rain (DR), while After Rain (AR) showed reduced mid-level saturation.
- Identified specific IRH thresholds at 700 hPa (0.82) and 150 hPa (0.70) that effectively identify DR and BR events while excluding NR cases.
Conclusions:
- Integrated Relative Humidity (IRH) provides a quantitative, layer-resolved metric for analyzing moisture-precipitation interactions.
- The findings demonstrate IRH's potential for nowcasting tools and enhancing meteorological model evaluation in subtropical environments.
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