GFS Noah Land Surface Model

Description

Land-atmosphere interactions are a main driver of Earth's surface water and energy budgets. The importance of the land surface is rather intuitive, and has been demonstrated not only in terms of predictability on daily to seasonal timescale ([8]), but also in terms of influencing extremes such as drought and heatwaves ([64]), PBL evolution and cloud formation ([62]) and afternoon convection ([29]), and tropical cyclone re-intensification ([2]). Other linkages, such as the role of soil moisture (SM) or vegetation heterogeneity in mesoscale circulation ([40]) and planetary waves ([51]), and those driven by land use and land cover change or management ([37]; [22]) are topics of active research.

Figure 1 is a schematic of local land-atmosphere interactions in a quiescent synoptic regime, including the soil moisture-precipitation (SM-P) feedback pathways. Solid arrows indicate a positive feedback pathway, and large dashed arrows represent a negative feedback, while red indicates radiative, black indicates surface layer and PBL, and brown indicates land surface processes. Thin red and grey dashed lines with arrows also represent positive feedbacks. The single horizontal gay-dotted line (no arrows) indicates the top of the PBL, and the seven small vertical dashed lines (no arrows) represent precipitation

Figure 1: Local Land-atmosphere Interaction (courtesy of Michael Ek, Ek and Mahrt (1994), Ek and Holtslag (2004))

Recently, the land surface updates in 2017 GFS operational physics includes:

• IGBP 20-type 1-km land classification
• STASGO 19-type 1-km soil classification
• MODIS-based snow free albedo
• MODIS-based maximum snow albedo
• Diurnal albedo treatment
• Unify snow cover, albedo between radiation and land surface model
• Increase ground heat flux under deep snow
• Upgrade surface layer parameterization scheme GFS Surface Layer Scheme to modify the roughness-length formulation and introduce a stability parameter constraint in the Monin-Obukhov similarity theory to prevent the land-atmosphere system from fully decoupling leading to excessive cooling of 2m temperature during sunset
  

  Figure 2: Land Data Sets Used in NCEP Modeling Systems

Intraphysics Communication

• GFS Noah LSM Driver (Argument Table)
• GFS Noah LSM Model (gfssflx())

General Algorithm

• GFS Noah Driver General Algorithm
• GFS Noah LSM General Algorithm