No abstract

We used a 3 yr data set of NOAA-AVHRR (Advanced Very High Resolution Radiometer) imagery to investigate cloud frequency, cloud-top height and cloud liquid water path for the Ecuadorean area, with special reference to a specific region in the Andes of southern Ecuador. In general, the seasonal cycle of cloudiness is significantly correlated to the spatial occurrence of the rainy seasons. However, we found that the complex topography of the Andes with dynamic effects at the windward and lee sides, as well as thermal breeze-systems, cause a specific spatial structure of cloud frequency and cloud properties. For instance, the eastern Andean slopes are mainly affected by a strong dynamic barrage effect of the easterlies, where a line of high cloud frequency occurs in the area of the Andes-occurring system (AOS) rain band. Average cloud-top height reveals a clear division between the Pacific area west of the western Cordillera chain, characterised by lower and more stratiform clouds, and the eastern parts of the country where an increase in average cloud-top height towards the Amazon indicates an intensification of convective cloud formation processes. This corresponds with the higher amounts of cloud liquid path over the Amazon, which illustrates that the cloud water cycle is more intensive in comparison to the Ecuadorian coastal plains. KEY WORDS: Ecuador · Clouds · NOAA-AVHRR Resale or republication not permitted without written consent of the publisherClim Res 30: [133][134][135][136][137][138][139][140][141][142][143][144][145][146][147] 2006 species in a submontane rain forest flowered during the peak of solar irradiance which was mainly a function of cloud cover.Satellite data are commonly used to overcome the limits of ground-based observations and models for the elaboration of cloud climatologies and weather/climate change forecasts. Global and regional cloud climatologies have been derived from comprehensive data sets of geostationary and polar orbiting systems, underlining the high potential of satellite imagery for cloud observations from space (e.g. International Satellite Cloud Climatology Project [ISCCP], cf. Schiffer & Rossow 1983, Rossow et al. 1985, Kästner & Kriebel 2001, Bendix 2002. New opportunities for cloud studies (especially regarding the investigation of cloud properties) have been opened up by novel technologies such as satellite-borne cloud radars (e.g. the Cloudsat mission, Stephens et al. 2002). However, the spatial resolution of the global data sets currently available (e.g. ISCCP) is too low to register local differences of cloudiness especially in a complex topography such as the Ecuadorian Andes.Some studies on the climate of Ecuador give an overview of climatic zones (Landívar 1977, 1989, Richter 2003 or examine the diurnal and seasonal course of wind velocity in the high Andes of Ecuador (Endlicher 1982). Most studies describe the seasonal variability of temperature and precipitation (Zimmerschied 1958, Bendix & Lauer 1992, Vuille et al. 2000, Sklenáȓ & Laegaard 2003 o...

No abstract

ABSTRACT:To date, the annual and diurnal pattern of low clouds touching the ground in tropical mountains is widely unknown. This holds true for the valley of the Rio San Francisco in southern Ecuador, and is mainly due to a lack of routine cloud observations, which is symptomatic for remote areas in tropical high mountains. A method to use a simple and cost-effective WebCam system for a quantitative analysis of cloud frequency as a proxy for the occurrence of low-cloud bases touching the ground is introduced. An interactive classification tool is developed, which is applied to a comprehensive dataset of 32 452 images (during the years 2002-2004) archived at 5 min intervals. The results point to a rapid increase of cloud frequency at altitudes >2600 m asl both during the day and the year, mainly caused by advective clouds veiling the crests of the Cordillera del Consuelo. Even if the formation of radiation fog directly at the valley bottom is nearly negligible with regard to the whole dataset, scatterometer measurements suggest that valley fog formation on the slopes is a regular process during the night, causing a clear drop in the cloud base around sunrise. The interaction of low-radiative and high-advective clouds is supposed to be the driving factor for a rainfall maximum at the valley bottom around sunrise. Higher values of cloud frequency still exist at the crest level around noon: these originate from well-developed upslope-breeze systems.

Mountain pastures dominated by the pasture grass Setaria sphacelata in the Andes of southern Ecuador are heavily infested by southern bracken (Pteridium arachnoideum), a major problem for pasture management. Field observations suggest that bracken might outcompete the grass due to its competitive strength with regard to the absorption of photosynthetically active radiation (PAR). To understand the PAR absorption potential of both species, the aims of the current paper are to (1) parameterize a radiation scheme of a two-big-leaf model by deriving structural (LAI, leaf angle parameter) and optical (leaf albedo, transmittance) plant traits for average individuals from field surveys, (2) to initialize the properly parameterized radiation scheme with realistic global irradiation conditions of the Rio San Francisco Valley in the Andes of southern Ecuador, and (3) to compare the PAR absorption capabilities of both species under typical local weather conditions. Field data show that bracken reveals a slightly higher average leaf area index (LAI) and more horizontally oriented leaves in comparison to Setaria. Spectrometer measurements reveal that bracken and Setaria are characterized by a similar average leaf absorptance. Simulations with the average diurnal course of incoming solar radiation (1998–2005) and the mean leaf–sun geometry reveal that PAR absorption is fairly equal for both species. However, the comparison of typical clear and overcast days show that two parameters, (1) the relation of incoming diffuse and direct irradiance, and (2) the leaf–sun geometry play a major role for PAR absorption in the two-big-leaf approach: Under cloudy sky conditions (mainly diffuse irradiance), PAR absorption is slightly higher for Setaria while under clear sky conditions (mainly direct irradiance), the average bracken individual is characterized by a higher PAR absorption potential. (∼74 MJ m−2 year−1). The latter situation which occurs if the maximum daily irradiance exceeds 615 W m−2 is mainly due to the nearly orthogonal incidence of the direct solar beam onto the horizontally oriented frond area which implies a high amount of direct PAR absorption during the noon maximum of direct irradiance. Such situations of solar irradiance favoring a higher PAR absorptance of bracken occur in ∼36% of the observation period (1998–2005). By considering the annual course of PAR irradiance in the San Francisco Valley, the clear advantage of bracken on clear days (36% of all days) is completely compensated by the slight but more frequent advantage of Setaria under overcast conditions (64% of all days). This means that neither bracken nor Setaria show a distinct advantage in PAR absorption capability under the current climatic conditions of the study area.