Surface Expressions of Atmospheric Thermal Tides in the Tropical Atlantic and Their Impact on Open-Ocean Precipitation

Christophersen, J. A.; Foltz, G. R.; Perez, R. C.

doi:10.1029/2019JD031997

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i

Surface Expressions of Atmospheric Thermal Tides in the Tropical Atlantic and Their Impact on Open-Ocean Precipitation

2020
By Christophersen, J. A. ; Foltz, G. R. ; Perez, R. C.
Source: Journal of Geophysical Research: Atmospheres, 125(22)

[PDF-4.28 MB]

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Journal Title:

Journal of Geophysical Research: Atmospheres
Personal Author:

Christophersen, J. A. ; Foltz, G. R. ; Perez, R. C.

Christophersen, J. A. ; Foltz, G. R. ; Perez, R. C. Less -
NOAA Program & Office:

OAR (Oceanic and Atmospheric Research) ; AOML (Atlantic Oceanographic and Meteorological Laboratory) ; CIMAS (Cooperative Institute for Marine and Atmospheric Studies)

OAR (Oceanic and Atmospheric Research) ; AOML (Atlantic Oceanographic and Meteorological Laboratory) ; CIMAS (Cooperative Institute for Marine and Atmospheric Studies) Less -
Description:

Diurnal and semidiurnal variations of atmospheric pressure and surface winds are fundamental to the Earth-Sun system. Past research in the tropical Pacific shows semidiurnal and diurnal patterns in the zonal and meridional wind anomalies, respectively. While the semidiurnal zonal wind pattern is consistent with atmospheric thermal tidal forcing, it is not yet certain what drives diurnal meridional wind variability. This study examines the diurnal cycle of meridional winds in the tropical Atlantic Ocean across four different seasons and the extent to which they impact the diurnal evolution of open-ocean precipitation in boreal summer. Comparisons of direct observations from long-term moored buoys to an atmospheric reanalysis (MERRA-2) show that MERRA-2 reproduces diurnal and semidiurnal pressure and wind variations. The MERRA-2 atmospheric thermal tides are decomposed into migrating and nonmigrating tidal components, and the linear terms in the zonal and meridional momentum equations are calculated. There is an approximate balance between the acceleration and pressure gradient terms for the zonal migrating momentum budget in the open ocean, with larger residuals or imbalances between those terms for the other budgets. The meridional nonmigrating budget shows largest residuals near the African coastline, indicating that nonlinear processes like the evening initiation of convection are important over land. This evening convection drives the meridional component of surface convergence which is translated offshore by the nonmigrating tide in the form of gravity waves, potentially modified by the African Easterly Jet. During boreal summer, this convergence helps to induce a morning peak of precipitation over the open ocean.
Keywords:

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Atmospheric tides
Source:

Journal of Geophysical Research: Atmospheres, 125(22)
DOI:

https://doi.org/10.1029/2019JD031997
Document Type:

Journal Article
Funding:

Grant no. NA20OAR4320472
Place as Subject:

Climatology
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Submitted
Main Document Checksum:

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urn:sha256:f68305c54071a79115960aa74ae885730434546eda05c23d51655307b2c14f93
Download URL:

https://repository.library.noaa.gov/view/noaa/27456/noaa_27456_DS1.pdf
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Surface Expressions of Atmospheric Thermal Tides in the Tropical Atlantic and Their Impact on Open-Ocean Precipitation

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