http://joewheatley.net Earth Vegetation Thu, 29 Jul 2010 15:16:55 +0000 http://backend.userland.com/rss092 en If you are a professional with interest in weather/climate impacts in agriculture Biospherica would like to hear your views. Please click here to take the online survey. It takes about 6 minutes. All questions are optional. Thanks! http://joewheatley.net/survey/ Weather and climatic variability affect vegetation on continental scales. Intuitively, healthy vegetation is greener. A quantitative index of "greenness" called Normalised Difference Vegetation Index (NDVI) was developed by NASA.  The index takes values between 0 and 1. NDVI is related to the fraction of photosynthetically active radiation absorbed by the ... http://joewheatley.net/response-of-african-vegetation-to-drought/ The impacts of drought depend on time-scale. On short time-scales, drought means dry soil. On long time-scales, it means dry rivers and empty reservoirs. A region may simultaneously experience dry conditions on one time-scale and wet conditions on another e.g. wet soil but low streamflow or visa versa. Standardized Precipitation Index ... http://joewheatley.net/visualizing-drought/ Weather is unpredictable. Small differences in initial conditions can develop into big differences in the pattern of circulation, in the timing and location of cyclones, rainfall etc. This is true no matter how good the initial observing system is. The approach taken by organisations such as ECMWF or NCEP is to ... http://joewheatley.net/ensemble-prediction/ Jet streams are narrow tubes of strong westerly winds which circle the earth at ≈ 10km elevation. These strong winds separate regions of cold and warm air. Surface weather at mid-latitudes is affected by the chaotic meanderings of jet streams. The above wind speed maps are based on NCEP GFS analysis at ... http://joewheatley.net/visualizing-the-jet-stream/ Just about everyone is familiar with weather maps. There are many situations where it is useful to combine the underlying numerical weather data with other types of information. Accessing  the weather data is a necessary first step. The output from the U.S. National Centers for Environmental Prediction (NCEP) Global  Forecast System ... http://joewheatley.net/ncep-global-forecast-system/ The global temperature record shows strong serial correlation. This boosts the uncertainty in the slope of the global warming trend. Here the uncertainty in the trend is derived using one of the satellite datasets. warming in the satellite era Data from satellites have been used to construct a global temperature record beginning ... http://joewheatley.net/serial-correlation-and-global-temperature-trend-uncertainty/ Recently (2008) the European Space Agency produced GlobCover (ESA GlobCover Project, led by MEDIAS-France), the highest resolution (300m) global land cover map to date. GlobCover uses 21 primary land cover classes and many more sub-classes. Land cover classification (LCC) schemes divide the earth into biomes. Biomes are the simplest way ... http://joewheatley.net/mapping-biomes/ [caption id="attachment_1075" align="aligncenter" width="790" caption="West of Ireland oak woodland - October 11 "][/caption] Flux tower eddy covariance instruments measure CO2 flux between an ecosystem and the atmosphere. Observed CO2 fluxes (also called NEE, Net Ecosystem Exchange) can be correlated with locally measured solar intensity, temperature, humidity etc. With enough data, a ... http://joewheatley.net/flux-towers-part-ii/ Most solar energy absorbed at the earth's surface is radiated back into space. For every high energy solar photon absorbed, about 20 degraded thermal photons are eventually radiated back. Ecosystems hitch a ride on this process. The starting point is of course plant photosynthesis which converts sunlight into chemical energy:  ... http://joewheatley.net/flux-towers-part-i/