Search Results

You are looking at 1 - 3 of 3 items for :

  • Author or Editor: A. M. Blyth x
  • Journal of Applied Meteorology and Climatology x
  • Refine by Access: All Content x
Clear All Modify Search
E. M. Blyth
and
A. J. Dolman

Abstract

A dual-source model that solves the energy balance over vegetation and soil separately can be inverted to obtain the roughness length for heat z 0h of a single-source model. Model parameters for the dual-source model were taken from previous analysis of data from a sparse canopy in semiarid terrain. In these circumstances, the value of z 0h , is shown to be dependent on the humidity deficit, the available energy, the vegetation fraction, and the surface resistance of the soil and the vegetation.

Full access
E. M. Blyth
,
A. J. Dolman
, and
J. Noilhan

Abstract

A meso-β-scale model is used to model a frontal intrusion in southwest France during HAPEX-MOBILHY. The skill of the model to reproduce the observed variation in temperature, humidity, and wind speed over the domain is reasonable within the limitations of the model parameterizations and initialization procedure, although there were errors in the timing and positioning of the front. A stable boundary layer was both observed and modeled over the forested area. The associated negative sensible heat flux provided the energy to sustain evaporation from the wet forest canopy under conditions of low radiation. A large wind shear over the stably stratified boundary layer provided the required turbulent kinetic energy to maintain the downward transport of sensible heat. Sensitivity experiments showed that local rainfall with a full forest cover changed from 2.9 to 3.8 mm, which represents a 30% increase when compared with a bare-soil domain. Half of this increase is from positive feedback of the intercepted water that reevaporates. The high roughness length of the forest, with its associated physical and dynamical effects, accounts for the rest of the increase in rainfall and for the accompanying increase in soil moisture.

Full access
Sonia Lasher-Trapp
,
Shailendra Kumar
,
Daniel H. Moser
,
Alan M. Blyth
,
Jeffrey R. French
,
Robert C. Jackson
,
David C. Leon
, and
David M. Plummer

ABSTRACT

The Convective Precipitation Experiment (COPE) documented the dynamical and microphysical evolution of convection in southwestern England for testing and improving quantitative precipitation forecasting. A strong warm rain process was hypothesized to produce graupel quickly, initiating ice production by rime splintering earlier to increase graupel production and, ultimately, produce heavy rainfall. Here, convection observed on two subsequent days (2 and 3 August 2013) is used to test this hypothesis and illustrate how environmental factors may alter the microphysical progression. The vertical wind shear and cloud droplet number concentrations on 2 August were 2 times those observed on 3 August. Convection on both days produced comparable maximum radar-estimated rain rates, but in situ microphysical measurements indicated much less ice in the clouds on 2 August, despite having maximum cloud tops that were nearly 2 km higher than on 3 August. Idealized 3D numerical simulations of the convection in their respective environments suggest that the relative importance of particular microphysical processes differed. Higher (lower) cloud droplet number concentrations slow (accelerate) the warm rain process as expected, which in turn slows (accelerates) graupel formation. Rime splintering can explain the abundance of ice observed on 3 August, but it was hampered by strong vertical wind shear on 2 August. In the model, the additional ice produced by rime splintering was ineffective in enhancing surface rainfall; strong updrafts on both days lofted supercooled raindrops well above the 0°C level where they froze to become graupel. The results illustrate the complexity of dynamical–microphysical interactions in producing convective rainfall and highlight unresolved issues in understanding and modeling the competing microphysical processes.

Full access