Abstract:The surface energy balance and near-surface weather variables were measured during the complete growth cycle of cotton and wheat crops planted in two successive seasons in 1995±1996 at a ®eld site in the Yaqui Valley in Sonora, Mexico. These data were analysed in terms of a set of simple evapotranspiration models, which included the Penman±Monteith equation applied at both the hourly and daily time-scales and four semiempirical simpli®cations of that equation. The ®eld data were used to investigate and specify seasonal variations in the surface parameters (crop coecient or surface resistance) appropriate to these models. There was a marked dierence between the eective value of surface parameters for the (cotton) row crop and the (wheat) continuous-cover crop during and immediately after periods of¯ood irrigation. This dierence re¯ects the fact that wet soil and remnant pools of irrigation water are well exposed to the atmosphere for¯ood-irrigated row crops and that evapotranspiration rates are enhanced. It proved possible to incorporate a description of this phenomenon by including a simple, additional term in an otherwise traditional model of the seasonal variation in crop factor or surface resistance. Once the parameters in the various models had been optimized against ®eld data, all the models provided reasonable descriptions of the measured evapotranspiration. However, the Penman±Monteith equation applied at the hourly time-scale performed least well and required greater parameterization; hence, its use in this application is not justi®ed. At the daily time-scale, use of the Penman± Monteith equation or Shuttleworth's reference crop evaporation (with a crop factor) is arguably preferable to the others in that, having more realism, it provides a description in which the (calibrated) surface parameters are a purer measure of crop control. However, in terms of descriptive ability after local calibration, the Penman, Priestley±Taylor, and Makkink models proved superior in this study. The good performance of the Makkink formulation is particularly encouraging because this equation requires only incoming solar radiation, which can be readily estimated from remotely sensed data. #

No abstract

No abstract

Abstract. Predictions of average surface temperature of a sparsely vegetated West-African savannah by both single and dual source models of surface energy partitioning are compared. Within the single source model, the ``excess resistance" to heat transfer away from the canopy (compared to momentum absorption) is characterised by parameter kB-1, where k is the von Kármán constant and B is the Stanton number. Two values of this parameter are used; first kB-1 = 2 (a value often used within surface energy balance models but primarily applicable to permeable vegetation types) and then 12.4 (a value applicable to the savannah in question, which consists more of bluff roughness elements). As expected, the latter parameterisation generates better predictions of surface temperature. To make accurate predictions of surface temperature using a dual source model, then that model’s in-canopy aerodynamic resistance must be increased. Information on this increase is found through direct model intercomparison with the single source model parameterised with kB-1 = 12.4. Keywords: Penman-Monteith equation; Surface temperature; Canopy resistance; Savannah; Dual-Source model

A case of primary leiomyosarcoma of the colon in a patient without gastrointestinal symptomatology who initially manifested a metastasis in the parotid region is described. Review of the literature indicates that mitotic activity is the most reliable histologic criterion for prognosis. Three of five patients with tumors manifesting high mitotic activity succumbed to widespread metastatic disease within four months of initial diagnosis. The prognosis is generally favorable for those patients whose neoplasms have low or moderate mitotic rates.