Nonlinear data assimilation in geosciences: an extremely efficient particle filter

Almost all research fields in geosciences use numerical models and observations and combine these using data-assimilation techniques. With ever-increasing resolution and complexity, the numerical models tend to be highly nonlinear and also observations become more complicated and their relation to the models more nonlinear. Standard data-assimilation techniques like (ensemble) Kalman filters and variational methods like 4D-Var rely on linearizations and are likely to fail in one way or another. Nonlinear data-assimilation techniques are available, but are only efficient for small-dimensional problems, hampered by the so-called ‘curse of dimensionality’. Here we present a fully nonlinear particle filter that can be applied to higher dimensional problems by exploiting the freedom of the proposal density inherent in particle filtering. The method is illustrated for the three-dimensional Lorenz model using three particles and the much more complex 40-dimensional Lorenz model using 20 particles. By also applying the method to the 1000-dimensional Lorenz model, again using only 20 particles, we demonstrate the strong scale-invariance of the method, leading to the optimistic conjecture that the method is applicable to realistic geophysical problems. Copyright c 2010 Royal Meteorological Society

"Han låter svensk" : En undersökning av svenskfödda lyssnares upplevelse av andraspråkstalares uttal

Uppsatsen bygger på en undersökning där ett eventuellt samband mellan svenskfödda lyssnares är upplevelse av vad som ett begripligt och lyssnarvänligt uttal hos andraspråkstalare, och durationen av de långa ljuden i betonade stavelser hos andraspråkstalare utreds. En lyssnargrupp bestående av 20 personer med svenska som förstaspråk fick lyssna på inspelningar av 6 andraspråkstalare som utifrån en bild och tio stödord skapade en berättelse. Lyssnarna betygsatte sedan talarnas uttal på skala från 1 till 6 utifrån kriterierna begriplighet och lyssnarvänlighet, och vid sidan av betygen gav de även skriftliga kommentarer om var och en av de sex talarna.           För att kunna bedöma och jämföra hur väl talarna lyckades realisera den komplementära längden användes talanalysprogrammet Praat. Undersökningen kan inte påvisa något samband mellan lyssnarnas betyg och talarnas förmåga att realisera den komplementära längden, men detta kan hänga samman med metodologiska problem. Lyssnarnas kommentarer visar emellertid på att flera talare lyssnar efter och värderar flyt högt och även att taltempot har en betydelse för upplevelsen av uttalet. Flyt definieras inte men ställt ofta i kontrast till ett hackigt uttal. Övriga faktorer som nämns i lyssnarnas kommentarer handlar ofta om segmentella och grammatiska faktorer och även om bland annat röststyrka och -kvalitet och om den berättartekniska förmågan.

Oesterreichs Militärverfassung in älter Zeiten.

Mode of access: Internet.

Dr. Rene Price (FCE LTER co-PI) installing a meteorological tower, Taylor Slough

This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DBI-0620409 and #DEB-9910514. This image is made available for non-commercial or educational use only.

FCE LTER research site TS/Ph-6b, Taylor Slough

This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DBI-0620409 and #DEB-9910514. This image is made available for non-commercial or educational use only.

A synthesis of long-term research by the Florida Coastal Everglades LTER Program

This paper synthesizes research conducted during the first 5–6 years of the Florida Coastal Everglades Long-Term Ecological Research Program (FCE LTER). My objectives are to review our research to date, and to present a new central theme and conceptual approach for future research. Our research has focused on understanding how dissolved organic matter (DOM) from upstream oligotrophic marshes interacted with a marine source of the limiting nutrient, phosphorus (P), to control productivity in the oligohaline estuarine ecotone. We have been working along freshwater to marine transects in two drainage basins located in Everglades National Park (ENP). The Shark River Slough transect (SRS) has a direct connection to the Gulf of Mexico, providing this estuarine ecotone with a source of marine P. The oligohaline ecotone along our southern Everglades transect (TS/Ph), however, is separated from this marine P source by the Florida Bay estuary. We originally hypothesized an ecosystem productivity peak in the SRS ecotone, driven by the interaction of marine P and Everglades DOM, but no such productivity peak in the TS/Ph ecotone because of this lack of marine P. Our research to date has tended to show the opposite pattern, however, with many ecosystem components showing enhanced productivity in the TS/Ph ecotone, but not in the SRS ecotone. Water column P concentrations followed a similar pattern, with unexpectedly high P in the TS/Ph ecotone during the dry season. Our organic geochemical research has shown that Everglades DOM is more refractory than originally hypothesized. We have also begun to understand the importance of detrital organic matter production and transport to ecotone dynamics and as the base of aquatic food webs. Our future research will build on this substantial body of knowledge about these oligotrophic estuaries. We will direct our efforts more strongly on biophysical dynamics in the oligohaline ecotone regions. Specifically, we will be focusing on inputs to these regions from four primary water sources: freshwater Everglades runoff, net precipitation, marine inputs, and groundwater. We are hypothesizing that dry season groundwater inputs of P will be particularly important to TS/Ph ecotone dynamics because of longer water residence times in this area. Our organic geochemical, biogeochemical, and ecosystem energetics work will focus more strongly on the importance of detrital organics and will take advantage of a key Everglades Restoration project, scheduled for 2008 or 2009, that will increase freshwater inputs to our SRS transect only. Finally, we will also begin to investigate the human dimensions of restoration, and of a growing population in south Florida that will become increasingly dependent on the Everglades for critical ecosystem services (including fresh water) even as its growth presents challenges to Everglades sustainability.

Dr. Justin Cummings presenting his field poster near TS/Ph-1 during the FCE LTER Mid-term Review field trip

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FCE LTER Mid-term Review field trip to TS/Ph-1

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FCE LTER Mid-term Review field trip to SRS-6

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FCE LTER Mid-term Review field trip to SRS-6

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