Preprints
https://doi.org/10.5194/amt-2021-295
https://doi.org/10.5194/amt-2021-295

  03 Dec 2021

03 Dec 2021

Review status: this preprint is currently under review for the journal AMT.

Boundary-layer height and surface stability at SMEAR II, Hyytiälä, Finland in ERA5 and observations

Victoria Anne Sinclair1, Jenna Ritvanen1,2, Gabin Urbancic2, Irina Statnaia1,2, Yurii Batrak3, Dmitri Moisseev1,2, and Mona Kurppa1 Victoria Anne Sinclair et al.
  • 1Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, PO BOX 64, FI-00014
  • 2Finnish Meteorological Institute, Helsinki, Finland
  • 3Development Centre for Weather Forecasting, Norwegian Meteorological Institute, Oslo, Norway

Abstract. The planetary boundary layer (BL) height and stratification are key parameters in determining the exchange of heat, momentum, moisture and trace gases between the surface and the free troposphere. Numerous different methods have been used to quantify the BL height and these methods have been applied to a wide variety of observational data sets obtained from different instruments and to numerical model output. We investigate the BL height at the Hyytiälä SMEAR II station in southern Finland diagnosed from radiosonde observations, a microwave radiometer (MWR) and ERA5 reanalysis. Four different algorithms are used to diagnose the BL height from the radiosondes. The diagnosed BL height is sensitive to the method used and the level of agreement, and the sign of systematic bias, between the 4 different methods depends on the surface-layer stability. For example, for very unstable situations, the median BL height diagnosed from the radiosondes varies from 600 m to 1500 m depending on which method is applied. Good agreement between the BL height in ERA5 and diagnosed from the radiosondes using Richardson number-based methods is found for almost all stability classes, suggesting that ERA5 has adequate vertical resolution near the surface to resolve the BL structure. However, ERA5 overestimates the BL height in very stable conditions highlighting the on-going challenge for numerical models to correctly resolve the stable BL. Furthermore, ERA5 BL height differs most from the radiosondes at 18 UTC suggesting ERA5 does not resolve the evening transition correctly. This study has also shown that BL height estimates from the MWR are reliable in unstable situations but often are inaccurate under stable conditions when, in comparison to ERA5 BL heights, they are much deeper. The errors in the MWR BL height estimates originate from the limitations of the manufacturers algorithm for stable conditions and also the mis-identification of the type of BL. A climatology of the annual and diurnal cycle of BL height and observed surface layer stability was created. The shallowest (353 m) monthly median BL height occurs in February and the deepest (576 m) in June. In winter there is no diurnal cycle in BL height, unstable BLs are rare yet so are very stable BLs. The shallowest BLs occur at night in spring and summer and very stable conditions are most common at night in the warm season. Finally, using ERA5 gridded data we determined that the BL height observed at Hyytiälä is representative of most land areas in southern and central Finland. However, the spatial variability of the BL height is largest during daytime in summer reducing the area over which BL height observations from Hyytiälä would be representative of.

Victoria Anne Sinclair et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2021-295', Anonymous Referee #2, 15 Dec 2021
  • RC2: 'Review report on amt-2021-295', Frank Beyrich, 20 Dec 2021

Victoria Anne Sinclair et al.

Victoria Anne Sinclair et al.

Viewed

Total article views: 347 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
275 69 3 347 22 2 0
  • HTML: 275
  • PDF: 69
  • XML: 3
  • Total: 347
  • Supplement: 22
  • BibTeX: 2
  • EndNote: 0
Views and downloads (calculated since 03 Dec 2021)
Cumulative views and downloads (calculated since 03 Dec 2021)

Viewed (geographical distribution)

Total article views: 338 (including HTML, PDF, and XML) Thereof 338 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 15 Jan 2022
Download
Short summary
We investigate the boundary-layer (BL) height and surface stability in southern Finland using radiosondes, a microwave radiometer and ERA5 reanalysis. Accurately quantifying the BL height is challenging and the diagnosed BL height can depend strongly on the method used. Microwave radiometers provide reliable estimates of the BL height but only in unstable conditions. ERA5 captures the BL height well except under very stable conditions which occur most commonly at night during the warm season.