High-Resolution Remote Sensing of the Gradient Richardson Number in a Megacity Boundary Layer

Yang, Simin and Ma, Yongjing and Zhang, Wenyu and Ren, Xinbing and Peng, Kecheng and Ahmad, Masroor and Jia, Danjie and Zhao, Dandan and Kong, Lingbin and Ma, Yining and Xin, Jinyuan (2024) High-Resolution Remote Sensing of the Gradient Richardson Number in a Megacity Boundary Layer. Remote Sensing, 16 (6). p. 1075. ISSN 2072-4292

[thumbnail of remotesensing-16-01075.pdf] Text
remotesensing-16-01075.pdf - Published Version

Download (7MB)

Abstract

The Gradient Richardson Number (Ri) is an important parameter for appraising the stability and turbulence exchange at the atmospheric boundary layer (ABL). However, high-resolution measurements of Ri profiles are rarely reported, especially in megacities. In this study, a Doppler wind lidar and a microwave radiometer were simultaneously utilized to measure the 2 km Ri vertical profile in downtown Beijing. These measurements were verified to have high accuracy compared with observations from a 325 m meteorological tower, with root-mean-square errors (RMSEs) of less than 1.66 K, 7.9%, and 1.45 m/s for the temperature, relative humidity, and wind speed (WS) for all altitudes and corresponding Pearson correlation coefficients (R) of 0.97, 0.93, and 0.81. The inter-comparisons of different spatial (25 m, 50 m, 100 m) and temporal resolutions (1 min, 30 min, 1 h) form a 3 × 3 resolution matrix of Ri, in which the 1 h temporal resolution of Ri overestimates the intensity and active area of turbulence. The Ri value retrieved from the 100 m spatial resolution data overestimates these by half as it misidentifies the height of the stable area at the near surface. There are significant differences between the data with a 1 min temporal resolution and a 25 m spatial resolution (defined as the standard resolution of Ri), and the rest of the data in the resolution matrix (defined as data at other resolutions), with an RMSE > 1 and an R < 0.8. The difference between data at the standard resolution and data at other resolutions increases with elevations, which results from frequent weather processes or from water-vapor blocking at higher altitudes. The Ri profiles reveal that the atmospheric layer at altitudes from 100 m to 500 m in daytime is unstable, with Ri < 0, while it is neutral, with 0 < Ri < 0.25, at night-time from 200 m to 400 m. The atmosphere above the ABL in a megacity is rather stable, with Ri > 0.25, whereas below the ABL, it is neutral or unstable, which is due to drastic changes in the WS and temperature that are affected by the topography and surface friction.

Item Type: Article
Subjects: OA Open Library > Multidisciplinary
Depositing User: Unnamed user with email support@oaopenlibrary.com
Date Deposited: 20 Mar 2024 10:12
Last Modified: 20 Mar 2024 10:12
URI: http://archive.sdpublishers.com/id/eprint/2572

Actions (login required)

View Item
View Item