Wind Limits on Rain Layers and Diurnal Warm Layers

Details

• Journal Title:
  Journal of Geophysical Research: Oceans
• Personal Author:
  Thompson, Elizabeth J. ; Moum, James N. ; Fairall, Christopher W. ; Rutledge, Steven A.
• NOAA Program & Office:
  CIRES (Cooperative Institute for Research in Environmental Sciences) ; OAR (Oceanic and Atmospheric Research) ; ESRL (Earth System Research Laboratory)
• Description:
  Stratification of the upper few meters of the ocean limits the penetration depth of wind mixing and the vertical distribution of atmospheric fluxes. Significant density stratification at depths ≤ 5 m was observed in 38% of a 2‐month data set from the central Indian Ocean collected during the DYNAMO experiment (Dynamics of the MJO, Madden‐Julian Oscillation). Diurnal warm layers (DWLs) formed by solar heating populated 30% of the data set and rain layers (RLs) populated 16%. Combined contributions from rain and insolation formed RL‐DWLs in 9% of the data set. RLs were detected at values of U 10 up to 9.8 m s−1, while DWLs were only detected at U 10 < 7.6 m s−1 (99th percentile values), symptomatic of the greater buoyancy flux provided by moderate to high rain rate compared to insolation. From the ocean friction velocity, u *w , and surface buoyancy flux, B , we derived estimates of urn:x-wiley:21699275:media:jgrc23188:jgrc23188-math-0001, stable layer depth, and urn:x-wiley:21699275:media:jgrc23188:jgrc23188-math-0002, the maximum U 10 for which stratification should persist at urn:x-wiley:21699275:media:jgrc23188:jgrc23188-math-0003 for fixed B . These estimates predicted (1) 36 out of 44 observed stratification events (88% success rate) and (2) the wind limits of these events, which are considered to be the 99th percentile values of U10). This suggests a means to determine the presence of ocean stable layers at depths ≤ 5 m from U 10 and B . Near‐surface stratification varied throughout two Madden‐Julian Oscillation (MJO) cycles. In suppressed MJO periods, (U 10 ≤ 8 m s−1 with strong insolation), RLs and RL‐DWLs were rare while DWLs occurred daily. During disturbed and active MJO periods, (U 10 ≤ 8 m s−1 with increased rain and cloudiness), multiple RLs and RL‐DWLs formed per day and DWLs became less common. When westerly wind bursts occurred, (U 10 = 7–17 m s−1 with steady rain), RLs formed infrequently and DWLs were not detected.
• Keywords:
  Boundary Layer Precipitation Boundary Layer
• Source:
  Journal of Geophysical Research: Oceans, ; 124, 897–924
• DOI:
  https://doi.org/10.1029/2018JC014130
• Document Type:
  Journal Article
• Rights Information:
  Other
• Compliance:
  Submitted
• Main Document Checksum:
  urn:sha-512:fe0360f4db9c7a76d4415068884b3b7313f788218439a02fd4027be16afc74ee44a6c7b120174e742b3d7aadf2617f21b08bef89f6e9f2bcb714b0e8f15e0c77
• Download URL:
  https://repository.library.noaa.gov/view/noaa/25182/noaa_25182_DS1.pdf
• File Type:
  [PDF - 4.49 MB ]