Planetary Boundary Layer Task Team

Improved monitoring, understanding, parameterization and modeling of ocean surface (air-sea interaction) and near-surface processes has been identified as a priority for TPOS 2020. Thus it was deemed important to develop a task team focused on air-sea interactions, specifically: diurnal variability, air-sea fluxes, and near-surface dynamics. This is particularly important as many essential ocean and climate variables are now derived from a combination of satellite and in situ data.

Project Function

The observational needs regarding improved monitoring and modelling of ocean surface and near-surface processes are likely to have two components: sustained detailed observations and process studies. It is the role of this Task Team to identify which requirements are best met via a sustained observing effort (> 5-11 years), and which can be addressed with specific short-term process campaigns.

Task Team Publications

  • Dec. 2014: Terms of Reference (see below)

 

Task Team Details

Task Team Members and Affiliations:

  • Meghan Cronin, NOAA Pacific Marine Environmental Lab, USA*
  • Tom Farrar, Woods Hole Oceanographic Institution, USA*
  • Anton Beljaars, European Centre for Medium-Range Weather Forecasts, United Kingdom
  • Frank Bryan, University Corporation for Atmospheric Research, USA
  • Michael Ek, National Center for Atmospheric Research, USA
  • Chris Fairall, NOAA Earth System Research Laboratory, USA
  • Kris Karnouskas, University of Colorado Boulder, USA
  • Jae Hak Lee, Korea Institute of Ocean Science and Technology, South Korea
  • Avichal Mehra, NOAA National Centers for Environmental Prediction, USA
  • Larry O’Neill, Oregon State University, USA
  • Roberto Rondanelli, University of Chile, Chile
  • Ken Takahashi, Instituto Geofiscio del Peru, Peru
  • Iwao Ueki, Japan Agency for Marine-Earth Science and Technology, Japan
  • Chidong Zhang, NOAA Pacific Marine Environmental Lab, USA

*Denotes Co-chairs

Terms of Reference

Starting with the background and context provided below, guidance from the TPOS white papers and other available reports, and taking into account both existing and near horizon capabilities:

  • Formulate a practical observing strategy and technical sampling requirement to ensure comprehensive air-sea fluxes can be estimated at hourly or better resolution across a set of key ocean and climate regimes in the tropical Pacific, covering the full suite of state variables to estimate heat, moisture, and momentum exchanges, including through use of bulk formula.
    • The Context provides a number of suggestions on possible regimes that the TT may use as a basis for identifying around five regimes with distinct characteristics.
  • Develop recommendations about the oceanic and atmospheric boundary layer measurements needed to meet TPOS objectives, and the space-time sampling required for those measurements. In particular, measurements that should resolve the diurnal cycle in the oceanic and atmospheric boundary layers will be identified.
  • Consider whether a subset of regimes where direct eddy-correlation approaches might be used is feasible and of value.
  • Liaise with the existing and developing ocean satellite and modelling community on efficiently meeting their present and future requirements for ocean surface data.
  • Engage biogeochemical and ecosystem experts to ensure the needs of key gas exchange calculations are met.
  • Liaise with the other TPOS 2020 Task Teams to maximize logistical and scientific synergies.
  • Carry out a risk analysis of the proposed approach (e.g., dependency on a single satellite mission or communications systems or ship time) and suggest possible mitigation strategies (e.g., some redundancy).

Background

Improved monitoring, understanding, parameterization and modeling of ocean surface (air-sea interaction) and near-surface processes has been identified as a priority for TPOS 2020. Many essential ocean and climate variables are now derived from a combination of satellite and in situ data. Supporting the observational needs of these synthesis activities is essential (e.g., GHRSST for SST). Thus satellite calibration/algorithm development and validation requirements along with product synthesis pathways need to be imbedded in the new TPOS 2020 design.
In addition, improved understanding is leading to new requirements. For instance the importance of the diurnal cycle in modulating SST and air-sea exchange is now apparent. The parameterization of fluxes (and boundary layer processes) under different regimes (stable/unstable boundary layer, sea wave state dependency, etc.) also need dedicated observations.

The observational needs regarding improved monitoring and modeling of ocean surface and near-surface processes are likely to have two components: sustained detailed observations and process studies. It is the role of this Task Team to identify which requirements are best met via a sustained observing effort (> 5 years), and which can be addressed with specific short-term process campaigns.

The TPOS 2020 white papers have identified some requirements and identified questions for discussion. For instance, in a future TPOS, should all buoys have velocity, salinity, temperature and meteorological state variables measured hourly? Higher vertical resolution is needed in the upper ocean – what are the exact needs? Are sites for direct measurements of flux-eddy correlation needed and, if so, where and how many? Is tying these specialised measurements to sites permanently the right strategy, or should they be moved around to cover different regimes?

It is also evident that so-called Large Eddy Simulations (LES) of the oceanic boundary layer can contribute to both the interpretation of ocean observations and to the development of improved parameterisations in models and within data assimilation systems. Such approaches show promise for improving understanding and representation of physical processes in the upper ocean.

The capabilities of present and near-horizon technologies should be taken into account when designing future configurations. The design of the backbone tropical Pacific observing system is being considered by another Task Team, and other Task Teams are focusing on other aspects of the TPOS 2020 Project. Liaison will be required with each of these teams and, in particular with those formulating plans for process studies in the eastern and Western Pacific.

Additional considerations within the context of TPOS 2020 activities:

  • The evolving backbone and Process Experiments
  • Emphasis on variability at diurnal, intra-seasonal (MJO), seasonal-interannual (ENSO) time scales, and prediction associated with the latter two.
  • Focus on distinguishable regimes, for example:
  • Eastern Boundary (Galapagos to coasts of Ecuador and Peru): LWnet minimum, reduced solar, Upwelling winds
  • Eastern Tropical Pacific (~130W to Galapagos): Maximum to net heat flux ( >120 W/m2)
  • Central Tropical Pacific (Range of migration of eastern extent of Warm Pool): Maximum variance in P
  • Western Warm Pool (region of net surface heat flux < 20 W/m2): Prime Indian Ocean coupling, Maximum P-E
  • Trade wind maximum/deep-sharp thermocline regime near 140W: Long history of boundary layer work; east edge of the warm pool
  • Off-equatorial regimes (e.g. SPCZ, ITCZ, stratus regions): Potentially important ocean-atmosphere interactions for decadal variability and/or climate change

Further elaboration of issues arising from the 1st TPOS SC meeting at KIOST, Ansan

Diurnal Coupling
1) Key diurnal process to observe and understand are upper ocean stratification due to solar heating, and night-time convection
2) Rectification as observed in SST; and expected in ocean mixing
3) Regimes of boundary layer coupling; (e.g. SST air-temperature coherences, leads-lags)
4) Observations for process modelling (e.g.LES) boundary conditions, forcing and verification

Surface Fluxes
1) Validation of satellite surface radiation products and NWP estimates
2) CAL/VAL for satellite precipitation
3) Bulk versus more direct turbulent fluxes (departures from “mean” transfer coefficients; wind wave conditions)
4) Regions of strong remote coupling with Indian Ocean