Mixing Diagrams

Uses the diurnal co-evolution of 2-meter temperature and specific humidity to return the contribution of surface fluxes and free troposphere entrainment fluxes on boundary layer moisture and heat. The balance between entrainment and surface fluxes informs the type of land-atmosphere coupling regime. There are also several thermodynamic variables that can be calculated and evaluated in conjunction with the 2-meter state variable co-evolutions such as the evaporative fraction and boundary layer height relationship, and the lifting condensation level deficit. See usage for more details.

Quantifies the heat and moisture entrainment fluxes at the top of the boundary layer, values that are incredibly difficult to quantify.

The Mixing Diagram approach is very powerful because these variables can be readily computed from observations and models enabling direct comparisons. This allows for tracking model development and comparing different models and reanalysis datasets against observations within the context of land-atmosphere coupling. See Figure 15 in Santanello et al. (2013) and Santanello et al. (2015).

The correlation and slope of the evaporative fraction (EF) and boundary layer height (PBL) relationship can be used to test inherent model behavior between surface fluxes and boundary growth. For example, if there is a strong correlation and slope between EF and PBL then boundary layer growth would likely be strongly tied to surface flux variability. This type of analysis can be calculated for observations and model output. See Figures 3 and 4 in Santanello et al. (2015).

Required Input Data:

2-meter temperature

2-meter specific humidity

surface latent heat flux

surface sensible heat flux

surface pressure

boundary layer height during the day.

For more precise calculations that include horizontal advection, wind speed (u and v components) and upwind specific humidity and temperature are required. This precise advection calculation is currently not included in the CoMeT, but could be added in future using center differencing.

It is often times difficult to define boundary layer height, so consistent definitions when making comparisons are desirable. Ideally, a mean boundary layer temperature and humidity should be used instead of 2m temperature and humidity, but the assumption is 2-m state variables are representative of the average boundary layer state. This assumption could lead to stronger contributions from surface fluxes if the measurement height is contained within the superadiabatic layer. Advection may also obscure the true influence of surface and entrainment fluxes, but this may be overcome if a fine enough time step is used relative to the advection time scale.