Surface Influences 8.2

From a numerical modeling standpoint, lower boundary conditions must be provided by

parameterization or explicit modeling of processes within the three layers

Land surfaces normally act as a

source of moisture (latent heat)

a day-time source of sensible heat

always as a momentum sink

The magnitude and patterns of surface fluxes may be constrained by

vegetation parameters

soil moisture

orographic effects

static stability

Over the ocean…

stronger winds intensify fluxes

spatial scales of sea surface temperature slowly vary

On near-surface conditions…

forcing from above is largely modulated by the local surrounding environment

Numerical forecast models and data assimilation schemes aim to describe

surface processes to better describe the sensible weather and hydrological impacts

In many cases, disparity of local conditions from numerical models and objective analyses is likely to be

largely related to surface processes

Regular monitoring of raw surface observations in concert with satellite and radar data is essential for what

to note weaknesses in automated products and to constrain forecasts to real world conditions

The three regions of the world in which land surface effects on convection have been intensely studied

The US Great Plains, the Amazon Basin, the West African Sahel

How is wind speed affected directly by changes in turbulent mixing?

Surface wind speeds are often strongest in the afternoon during the most intense mixing.

At night, increasing stability decouples the surface layer, calming the winds

The diurnal variation of relative humidity is mostly an effect of

temperature changes

Heat lows

Weak synoptic-scale low-pressure systems that occur over desert regions under periods of intense surface heating

Heat lows do not

move appreciably on synoptic timescales

have a definite center

and seasonally may transition into tropical lows or monsoon troughs

Diurnal cycles of cyclonic inflow and pressure in heat lows vary…

due to effects of topography and other geographical features