Investigation of hydrostatic imbalance with field observations

The hydrostatic equilibrium addresses the approximate balance between the positive force of the vertical pressure gradient and the negative gravity force and has been widely assumed for atmospheric applications. The hydrostatic imbalance of the mean atmospheric state for the acceleration of vertical motions in the vertical momentum balance is investigated using tower, the global positioning system radiosonde, and Doppler lidar and radar observations throughout the diurnally varying atmospheric boundary layer (ABL) under clear-sky conditions. Because of the negligibly small mean vertical velocity, the acceleration of vertical motions is dominated by vertical variations of vertical turbulent velocity variances. The imbalance is found to be mainly due to the vertical turbulent transport of changing air density as a result of thermal expansion/contraction in response to air temperature changes following surface temperature changes. In contrast, any pressure change associated with air temperature changes is small, and the positive vertical pressure-gradient force is strongly influenced by its background value. The vertical variation of the turbulent velocity variance from its vertical increase in the lower convective boundary layer (CBL) to its vertical decrease in the upper CBL is observed to be associated with the sign change of the imbalance from positive to negative due to the vertical decrease of the positive vertical pressure-gradient force and the relative increase of the negative gravity force as a result of the decreasing upward transport of the low-density air. The imbalance is reduced significantly at night but does not steadily approach zero. Understanding the development of hydrostatic imbalance has important implications for understanding large-scale atmosphere, especially for cloud development.

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Related Links

Related Dataset #1 : NCAR/EOL 915MHz Wind Profiler NIMA Winds and Moments. Version 1.0

Related Dataset #2 : NCAR/EOL Quality Controlled Radiosonde Data - ISS2 Rogers Farm Site. Version 1.0

Related Dataset #3 : 5 Minute Statistics of ISFF data during CASES-99. Version 1.0

Related Dataset #4 : Dataset for publication: Investigation of Hydrostatic Imbalance with Field Observations

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Author Sun, J.
Wulfmeyer, V.
Späth, F.
Vömel, Holger
Brown, William O.J.
Oncley, Steven
Publisher UCAR/NCAR - Library
Publication Date 2024-01-01T00:00:00
Digital Object Identifier (DOI) Not Assigned
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Topic Category geoscientificInformation
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Metadata Date 2025-07-10T20:05:23.309435
Metadata Record Identifier edu.ucar.opensky::articles:26908
Metadata Language eng; USA
Suggested Citation Sun, J., Wulfmeyer, V., Späth, F., Vömel, Holger, Brown, William O.J., Oncley, Steven. (2024). Investigation of hydrostatic imbalance with field observations. UCAR/NCAR - Library. https://n2t.org/ark:/85065/d72b9353. Accessed 01 August 2025.

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