Recent work has produced the following two (separate) results. First, the amount and distribution of surface characteristics such as soil moisture and vegetation, at large spatial scales (e.g., hundreds to thousands of km), can impact precipitation amount and spatial distribution at similarly large scales and over timescales of months/seasons. Second, at much smaller scales (e.g., 5-100 km) surface heterogeneity can force lower-tropospheric circulations (“mesoscale” circulations) that can impact local vertical heat and moisture transport as well as local cloudiness and precipitation.

Conceptually, we wish to link these two sets of mechanisms, occurring at distinct scales, into a more unified picture of land-atmosphere feedbacks across spatial scales from mesoscale to synoptic and across timescales from hourly to seasonal. The investigation of the potential links focuses initially on two questions. First, how do precipitation systems driven by large-scale (synoptic-scale) dynamics in a given region produce much smaller-scale (mesoscale) heterogeneity in soil moisture that might in turn drive local mesoscale circulations? Second, to what degree do surface-heterogeneity-forced mesoscale circulations impact the large-scale means (and higher-order statistics) of surface quantities such as soil moisture, and atmospheric quantities such as low-level stability, moist static energy, and vertical motion, that are expected to influence large-scale convective precipitation? The focus is on the time evolution of these two processes over the monthly/seasonal timescale. The approach is to use fine-resolution simulations with the Regional Atmospheric Modeling System (RAMS) over a portion of the GCIP domain during the Enhanced Seasonal Observing Periods (ESOPs) of 1995, 1996, and 1997. These simulations, in spite of being carried out at high spatial resolution and therefore being computationally intensive, incorporate the following key features: the coupling of an interactive land with the atmosphere; a realistic representation of the large-scale meteorology; and a long (for the given spatial resolution) simulation time.

Among the preliminary results are the following: (i) Evaporation-dominated regimes tend to have decreasing mesoscale surface flux heterogeneity with time, while precipitation events will tend to “recharge” the mesoscale heterogeneity; this is due to the (usually) smaller characteristic scale of precipitation vs. evaporation (radiation) variability. (ii) Days with more, and more intense, landscape-forced mesoscale circulations experience a re-distribution of water and thermal energy from the lower to the upper part of the boundary layer, with corresponding implications for the mean (over large spatial scales) atmospheric profile. (iii) Feedback processes can at times bridge the gap between these two scale ranges, resulting in coupled variability at the large-scale and mesoscale.