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Surface Heat Flux and its Association with the MJO in the Tropical Western Pacific using ARM Observations

Active Dates 9/1/2022-5/31/2024
Program Area Atmospheric System Research
Project Description
Surface heat flux and its association with the MJO in the tropical western Pacific using ARM observations

Pallav Ray, Florida Institute of Technology (PI)

Steven Lazarus, Florida Institute of Technology (Co-I)

Michael Splitt, Florida Institute of Technology (Co-I)

The changes in surface temperature and its adjacent atmospheric layers depend on the amount of energy coming or leaving the surface. A vital component of the earth’s surface energy budget is the surface heat flux, which is comprised of latent heat flux, sensible heat flux, longwave radiation, and shortwave radiation. The variability in surface heat flux is a first-order driver in the Madden-Julian oscillation (MJO), the most dominant mode of all tropical intraseasonal (20-100 day) variability. Modulation in convection appears to be driven by net surface heat flux modulation on intraseasonal time scales, particularly over the tropical western Pacific (TWP) and the Maritime Continent (MC). While surface heat flux variations drive sea surface temperature variability on the intraseasonal time scale, the variability is different over the MC due to the presence of land. As a result, a systematic study using in situ observations from the three Department of Energy – Atmospheric Radiation Measurement (DOE-ARM) Program sites in the TWP (Manus, Nauru, and Darwin) is essential in order to determine the surface heat flux–MJO relationship. In particular, using ARM datasets, we propose to:

(i) document the observed (i.e., ARM-based) evolution of surface heat fluxes at different temporal scales. The surface heat flux in the TWP exhibits variability on a wide variety of temporal (sub-diurnal to multi-decadal) and spatial (meso to planetary) scales. A particular emphasis will be given to understanding the diurnal cycle in fluxes based on ARM data since reanalysis and satellite observations have significant uncertainties at diurnal time scales compared to longer timescales;

(ii) describe the observed relationship between the MJO-associated convection and surface heat flux. This analysis, conducted using the entire ARM period over different MJO phases, propagation modes, seasons, and climate regimes (e.g., El-Niño versus non-El-Niño years), is expected to reveal a more complete view of the MJO-surface heat flux relationship over the TWP;

(iii) estimate the precipitation-induced surface sensible heat flux. One of the surface heat flux components that is often not considered is the surface sensible heat flux due to precipitation (QP). Since raindrops are typically cooler than the land or ocean surface, precipitation cools the land or ocean surface temperature. We propose to quantify the evolution of QP and its relative magnitude compared to other components of the surface heat fluxes based on ARM observations for the first time.

(iv) utilize ARM observations for classroom teaching, and familiarize and process parameters to develop future research ideas.

This work would improve our understanding of the role of surface heat flux on the amplitude and propagation of the MJO in the TWP. The ARM data will also be used for undergraduate Capstone projects, and in graduate-level courses. Moreover, bringing together expertise from scientists with different backgrounds, including both observational scientists and modelers, will help in building institutional capacities – a key outcome intended by this FOA. Our processed data and value-added products (such as daily, monthly and seasonal climatology of fluxes) from ARM sites are expected to serve as a benchmark for validation of reanalysis and model simulations. We fully commit to sharing any datasets that result from this project.

The MJO modulates the global atmospheric circulation. A host of extreme events that affect the U.S., from flooding precipitation to tornadoes to heavy snow to hurricanes, depends on an accurate representation and prediction of MJOs over the TWP. Hence, MJO propagation and how it is influenced by the surface heat flux in the TWP needs further attention. An improved understanding of the MJO-surface heat flux relationship will lead to better models and predictions in the TWP (and elsewhere) and will improve and inform decision-making within our communities and the private sector on the subseasonal-to-seasonal (S2S) time scale. The project will also train a number of students in the processing and analysis of DOE ARM observations.
Award Recipient(s)
  • Florida Institute of Technology Melbourne (PI: Ray, Pallav)