Distribution by Scientific Domains
Distribution within Life Sciences

Kinds of Assimilation

  • ammonium assimilation
  • carbon assimilation
  • co2 assimilation
  • cultural assimilation
  • data assimilation
  • genetic assimilation
  • high assimilation
  • n assimilation
  • net assimilation
  • net co2 assimilation
  • nitrate assimilation
  • nitrogen assimilation
  • nutrient assimilation
  • spatial assimilation
  • variational data assimilation

  • Terms modified by Assimilation

  • assimilation efficiency
  • assimilation model
  • assimilation pattern
  • assimilation process
  • assimilation rate
  • assimilation scheme
  • assimilation system

  • Selected Abstracts


    EVOLUTION, Issue 7 2003
    Massimo Pigliucci
    Abstract., The idea of genetic assimilation, that environmentally induced phenotypes may become genetically fixed and no longer require the original environmental stimulus, has had varied success through time in evolutionary biology research. Proposed by Waddington in the 1940s, it became an area of active empirical research mostly thanks to the efforts of its inventor and his collaborators. It was then attacked as of minor importance during the "hardening" of the neo-Darwinian synthesis and was relegated to a secondary role for decades. Recently, several papers have appeared, mostly independently of each other, to explore the likelihood of genetic assimilation as a biological phenomenon and its potential importance to our understanding of evolution. In this article we briefly trace the history of the concept and then discuss theoretical models that have newly employed genetic assimilation in a variety of contexts. We propose a typical scenario of evolution of genetic assimilation via an intermediate stage of phenotypic plasticity and present potential examples of the same. We also discuss a conceptual map of current and future lines of research aimed at exploring the actual relevance of genetic assimilation for evolutionary biology. [source]


    JOURNAL OF PHYCOLOGY, Issue 5 2008
    Luz E. De-Bashan
    Enzymatic activities of glutamate dehydrogenase (GDH) and glutamine synthetase (GS) participating in the nitrogen metabolism and related ammonium absorption were assayed after the microalga Chlorella vulgaris Beij. was jointly immobilized with the microalgae-growth-promoting bacterium Azospirillum brasilense. At initial concentrations of 3, 6, and 10 mg · L,1 NH4+, joint immobilization enhances growth of C. vulgaris but does not affect ammonium absorption capacity of the microalga. However, at 8 mg · L,1 NH4+, joint immobilization enhanced ammonium absorption by the microalga without affecting the growth of the microalgal population. Correlations between absorption of ammonium per cell and per culture showed direct (negative and positive) linear correlations between these parameters and microalga populations at 3, 6, and 10 mg · L,1 NH4+, but not at 8 mg · L,1 NH4+, where the highest absorption of ammonium occurred. In all cultures, immobilized and jointly immobilized, having the four initial ammonium concentrations, enzymatic activities of Chlorella are affected by A. brasilense. Regardless of the initial concentration of ammonium, GS activity in C. vulgaris was always higher when jointly immobilized and determined on a per-cell basis. When jointly immobilized, only at an initial concentration of 8 mg · L,1 NH4+ was GDH activity per cell higher. [source]


    JOURNAL OF PHYCOLOGY, Issue 4 2004
    Neill G. Barr
    Ammonium is assimilated in algae by the glutamine synthetase (GS),glutamine:2-oxoglutarate aminotransferase pathway. In addition to the assimilation of external ammonium taken up across the cell membrane, an alga may have to reassimilate ammonium derived from endogenous sources (i.e. nitrate reduction, photorespiration, and amino acid degradation). Methionine sulfoximine (MSX), an irreversible inhibitor of GS, completely inhibited GS activity in Ulva intestinalis L. after 12 h. However, assimilation of externally derived ammonium was completely inhibited after only 1,2 h in the presence of MSX and was followed by production of endogenous ammonium. However, endogenous ammonium production in U. intestinalis represented only a mean of 4% of total assimilation attributable to GS. The internally controlled rate of ammonium uptake (Vi) was almost completely inhibited in the presence of MSX, suggesting that Vi is a measure of the maximum rate of ammonium assimilation. After complete inhibition of ammonium assimilation in the presence of MSX, the initial or surge (Vs) rate of ammonium uptake in the presence of 400 ,M ammonium chloride decreased by only 17%. However, the amount that the rate of ammonium uptake decreased by was very similar to the uninhibited rate of ammonium assimilation. In addition, the decrease in the rate of ammonium uptake in darkness (in the absence of MSX) in the presence of 400 ,M ammonium chloride matched the decrease in the rate of ammonium assimilation. However, in the presence of 10 ,M ammonium chloride, MSX completely inhibited ammonium assimilation but had no effect on the rate of uptake. [source]

    Predicting world health organization toxic equivalency factor dioxin and dioxin-like polychlorinated biphenyl levels in farmed atlantic salmon (Salmo salar) based on known levels in feed

    Marc H. G. Berntssen
    Abstract Assimilation and elimination rate constant of dietary polychlorinated dibenzo- p -dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DLPCBs) with a World Health Organization toxic equivalency factor (WHO-TEF) were estimated in market-size Atlantic salmon (Salmo salar) using fish that were previously fed vegetable oil,based (low in PCDD/Fs and DLPCBs) or fish oil,based (high in PCDD/Fs and PCBs) diets. At the start of the kinetic trial, half the fish that were fed fish oils were fed vegetable oil feeds and inverted (cross-over design) for five months. The assimilation efficiencies of the PCDD/F congeners were more variable (3,89%) and, generally, were lower than those of the DLPCBs (70,80%). Among the PCDD/F congeners, the assimilation efficiency of the most toxic tetra- and pentachlorinated PCDD/Fs was greater than that of higher-chlorinated PCDD/Fs. Elimination rates for DLPCBs were higher than those for PCDD/Fs. Lower-chlorinated PCDDs had a lower elimination rate than the higher-chlorinated PCDDs, but no differences were observed among PCDF congeners or DLPCB congeners. Kinetic parameters were used to predict the level of WHO-TEF dioxins and DLPCBs in Atlantic salmon reared in a large-scale facility under commercial conditions. Predictions were based on preanalyzed levels of these organochlorines in feeds with three different replacement levels (0, 30, and 60%) of vegetable oil. A simple one-compartmental, first-order kinetic model was used to predict the level of sum WHO toxic equivalents for PCDD/Fs and DL-PCBs. The predicted values varied by 0 to 11% from the measured values in the commercially reared salmon. [source]

    Interactive effects of water table and precipitation on net CO2 assimilation of three co-occurring Sphagnum mosses differing in distribution above the water table

    Abstract Sphagnum cuspidatum, S. magellanicum and S. rubellum are three co-occurring peat mosses, which naturally have a different distribution along the microtopographical gradient of the surface of peatlands. We set out an experiment to assess the interactive effects of water table (low: ,10 cm and high: ,1 cm) and precipitation (present or absent) on the CO2 assimilation and evaporation of these species over a 23-day period. Additionally, we measured which sections of the moss layer were responsible for light absorption and bulk carbon uptake. Thereafter, we investigated how water content affected carbon uptake by the mosses. Our results show that at high water table, CO2 assimilation of all species gradually increased over time, irrespective of the precipitation. At low water table, net CO2 assimilation of all species declined over time, with the earliest onset and highest rate of decline for S. cuspidatum. Precipitation compensated for reduced water tables and positively affected the carbon uptake of all species. Almost all light absorption occurred in the first centimeter of the Sphagnum vegetation and so did net CO2 assimilation. CO2 assimilation rate showed species-specific relationships with capitulum water content, with narrow but contrasting optima for S. cuspidatum and S. rubellum. Assimilation by S. magellanicum was constant at a relatively low rate over a broad range of capitulum water contents. Our study indicates that prolonged drought may alter the competitive balance between species, favoring hummock species over hollow species. Moreover, this study shows that precipitation is at least equally important as water table drawdown and should be taken into account in predictions about the fate of peatlands with respect to climate change. [source]

    Negotiating Assimilation: Chicago Catholic High Schools' Pursuit of Accreditation in the Early Twentieth Century

    Ann Marie Ryan

    Assimilation and Otherness: the Theological Significance of Négritude

    This article argues that otherness is a root concept in Christian theology, functioning as such in Christology and the doctrines of the Trinity, creation, sanctification and consummation. Recent philosophical and theological treatments of otherness or alterity have, however, focused on its problematic aspects, its link to ills such as racism, sexism and genocide. The thought of the Senegalese statesman and poet Léopold Sédar Senghor (1906,2001) is proposed as an aid in mediating between the tradition's conceptions of otherness and contemporary debates and contexts, illuminating root concepts which have not been recognized as such, their systematic interconnectedness and their enduring relevance. [source]

    Migrant Assimilation in Europe: A Transnational Family Affair1

    Sam Scott
    The paper advances our empirical and theoretical understanding of migrant assimilation. It does so by focusing on a very particular group of individuals who appear more likely than other migrant types to "go native." We call these individuals "mixed nationality relationship migrants" (i.e., migrants who have committed to a life outside their home country because of the presence of a foreign partner). The paper argues that the transnational family milieus that emerge from this form of international migration are critical to the assimilation process. Empirical material from 11 in-depth interviews with female migrants in Britain (Sheffield) and France (Paris) supports our argument. We also suggest that such "extreme" assimilation is more likely within a regional migratory system , like the EU , where the "identity frontiers" crossed in the formation of a transnational family are relatively shallow. [source]

    "Reactive Ethnicity" or "Assimilation"?

    Arguments, First Empirical Evidence for Labor Migrants in Germany, Statements
    In this article, we scrutinize the often stated assumption that labor migrants in Germany turn away from integration and reaffirm their ethnicity by examining their identificational, cognitive, and social assimilation processes. Using data from the German Socio-economic Panel, we present trend analyses of different hostland- and homeland-related indicators for the past fifteen years. Results are presented separately for first- and second-generation migrants from Turkey, the EU, and the former Yugoslavia. While not all assimilation-related indicators change a great deal over time, they show at least a substantial difference between the first and the second generation. With regard to the homeland-related indicators, the results by no means suggest that Turkish migrants try to compensate for their comparatively disadvantaged social status by revitalizing ethnic cultural habits or homeland-oriented identifications. [source]

    Geographic Mobility and Spatial Assimilation among U. S. Latino Immigrants,

    Scott J. South
    Although the spatial assimilation of immigrants to the United States has important implications for social theory and social policy, few studies have explored the atterns and determinants of interneighborhood geographic mobility that lead to immigrants'residential proximity to the white, non-Hispanic majority. We explore this issue by merging data from three different sources - the Latino National Political Survey, the Panel Study of Income Dynamics, and tract-level census data - to begin unraveling causal relationships among indicators of socioeconomic, social, cultural, segmented, and spatial assimilation. Our longitudinal analysis of 700 Mexican, Puerto Rican, and Cuban immigrants followed from 1990 to 1995 finds broad support for hypotheses derived from the classical account of minority assimilation. High income, English language use, and embeddedness in Anglo social contexts increase Latino immigrants'geographic mobility into Anglo neighborhoods. U. S. citizenship and years spent in the United Stares are ppsidvely associated with geographic mobility into more Anglo neighbor oods, and coethnic contact is inversely associated with this form of mobility, but these associations operate largely through other redictors. Prior experiences of ethnic discrimination increase and residence in public housing decreases the likelihood that Latino immigrants will move from their origin neighborhoods, while residing in metropolitan areas with large Latino populations leads to geographic moves into "less Anglo" census tracts. [source]

    Gender and Ethnic Differences in Marital Assimilation in the Early Twentieth Century,

    Sharon Sassler
    Historical research on intermarriage has overlooked how distinctive patterns of ethnic settlement shape partner choice and assumed that the mate selection process operated the same way for men and women. This study utilizes a sample of youn married adults drawn from the 1910 Census IPUMS to examine 1) whether ethnic variation in partner choice was shaped by differences in group concentration and distribution and 2) if factors shaping outmarriage were gendered. About one fifth of young married Americans had spouses of a different ethnic background in 1910, though there was considerable ethnic variation in outmarriage propensities. Barriers to intermarriage fell at different rates, depending upon ethnic grou, sex, and region of settlement; they were weakest for first-and seconl eneration English men. Structural factors such as group size operatef differently for men and women; while larger group representation increased men's odds of outmarriage to both native stock and other white ethnic wives, women from the ethnic groups with the largest presence were significantly more likely to wed fellow ethnics than the native stock. Ultimately, even if they resided in the same location, the marriage market operated in different ways for ethnic women and men in search of mates. [source]

    Exploring Diversity in Immigrant Assimilation and Transnationalism: Poles and Russian Jews in Philadelphia,

    Ewa Morawska
    This article investigates different patterns of coexistence of assimilation and transnational engagements (A/T) among recent Polish and Jewish Russian immigrants in Philadelphia and the particular constellations of circumstances that generate these outcomes. It then integrates this analysis into a broader comparative examination of the simultaneity of A/T among residentially dispersed Asian Indians, first-wave Cubans in Miami, and Jamaicans, undocumented Chinese, and Dominicans in New York. The main factors shaping the most common A/T patterns in these seven immigrant groups at the global, sending and receiving society national, and local levels are identified. [source]

    Assimilation, Ethnic Competition, and Ethnic Identities of U.S.-Born Persons of Mexican Origin

    Hiromi Ono
    Processes governing the ethnic identification of second and later generations of Mexican immigrant descendants are explored empirically using the Latino National Political Survey, 1989,1990. With multinomial logit regressions, I test hypotheses based on three contrasting perspectives, namely, that ethnic identification, or identification other than "American," arises directly from: a) cultural continuity and a lower level of assimilation; b) an experience of ethnic competition; and c) both processes. The results from the LNPS support the view that both processes are at work. For example, consistent with the presence of an assimilation process, the chance of "Mexican" identification (as opposed to "American" identification) declines to half in the third generation and to one tenth in the fourth and later generations, relative to the chance in the second generation. Consistent with the presence of an ethnic competition process, (perceived) experience of discrimination doubles the respondent's chance of "Mexican" identification. Also, a level rise in the darkness of skin color is associated with a 60 percent increase in the chance of Mexican identification. [source]

    Assimilation and contrast in optical illusions1

    Abstract: This study has focused on how assimilation and contrast correlate with the generating processes of various optical illusions. First of all, we defined the meanings of assimilation and contrast from two viewpoints, namely, phenomena and mechanisms. We then examined the characteristic appearances of the Delboeuf illusion as a typical size illusion caused by assimilation and contrast, by referring to major studies on this illusion in Japan. To confirm the different size-judgment processes operating in size illusions of concentric circles, quadrilaterals, lines, and angles, we explored the magnitude of illusion, including peak and conversion from overestimation to underestimation. The consistent occurrences of peak and conversion indicated the antagonistic correlations of assimilation and contrast in the generation of these illusions. Manipulation of figural unification using solid and non-solid segments had no effect on these illusions, which were constructed almost by their own specific contour-patterns. Finally, we tried to incorporate assimilation and contrast into our proposition that the combination of three factors (angle/direction, space/position, and assimilation/contrast) explains the generation of many optical illusions. [source]

    Effects of Elevated CO2 on Growth, Carbon Assimilation, Photosynthate Accumulation and Related Enzymes in Rice Leaves during Sink-Source Transition

    Jun-Ying Li
    Abstract To study the effects of growing rice (Oryza sativa L.) leaves under the treatment of the short-term elevated CO2 during the period of sink-source transition, several physiological processes such as dynamic changes in photosynthesis, photosynthate accumulation, enzyme activities (sucrose phosphate synthase (SPS), and sucrose synthase (SS)), and their specific gene (sps1 and RSus1) expressions in both mature and developing leaf were measured. Rice seedlings with fully expanded sixth leaf (marked as the source leaf, L6) were kept in elevated (700 ,mol/mol) and ambient (350 mol/L) CO2 until the 7th leaf (marked as the sink leaf, L7) fully expanded. The results demonstrated that elevated CO2 significantly increased the rate of leaf elongation and biomass accumulation of L7 during the treatment without affecting the growth of L6. However, in both developing and mature leaves, net photosynthetic assimilation rate (A), all kinds of photosynthate contents such as starch, sucrose and hexose, activities of SPS and SS and transcript levels of sps1 and RSus1 were significantly increased under elevated CO2 condition. Results suggested that the elevated CO2 had facilitated photosynthate assimilation, and increased photosynthate supplies from the source leaf to the sink leaf, which accelerated the growth and sink-source transition in new developing sink leaves. The mechanisms of SPS regulation by the elevated CO2 was also discussed. [source]

    Measures of Assimilation in the Marriage Market: Mexican Americans 1970,1990

    Michael J. Rosenfeld
    In 1965 the United States rewrote its immigration laws, and immigration increased sharply as a result. The immigrants and the children of immigrants from the post-1965 period are slowly becoming more influential in U.S. life; the largest of these groups are the Mexican immigrants and the Mexican Americans. The rapid growth of Hispanic and Asian populations in the United States has led to a renewed interest in the question of assimilation; that is, will the new groups assimilate, and if so how long will it take? Will they become part of White America? Will some groups assimilate into the Black-dominated urban underclass (a process Portes called segmented assimilation)? Will some groups remain permanently separate and socially isolated? In this article, I examine the behavior of Mexican Americans and Mexican immigrants in the U.S. marriage market, using census data from 1970, 1980, and 1990. The findings are that Mexican Americans are assimilating with non-Hispanic Whites over time, and the evidence tends to reject the segmented assimilation hypothesis. The interplay between intermarriage and endogamy is studied with log linear models; some variations by geography and U.S. nativity are noted. [source]

    From Old Testament to New: A. P. Elkin on Christian Conversion and Cultural Assimilation

    Russell McGregor

    Discursive identity: Assimilation into the culture of science and its implications for minority students

    Bryan A. Brown
    This study examined how, in some instances, participation in the cultural practices of high school science classrooms created intrapersonal conflict for ethnic minority students. Discourse analysis of videotaped science classroom activities, lectures, and laboratories was the primary methodology employed for analyzing students' discursive identity development. This analysis demonstrated differential appropriation of science discourse as four significant domains of discursive identities emerged: Opposition status, Maintenance status, Incorporation status, and Proficiency status. Students characterized as Opposition Status avoided use of science discourse. Students who exhibited Maintenance Status illustrated a commitment to maintaining their normative discourse behavior, despite a demonstrated ability to appropriate science discourse. Students characterized as Incorporation Status made active attempts to incorporate science discourse into their normative speech patterns, while Proficiency Status students demonstrated a fluency in applying scientific discursive. Implications for science education emerging from the study include the illumination of the need to make the use of specific scientific discourse an explicit component of classroom curriculum. © 2004 Wiley Periodicals, Inc. J Res Sci Teach 41: 810,834, 2004 [source]

    Digestion and Assimilation of the Free-living Nematode Panagrellus redivivus Fed to First Feeding Coregonid Larvae: Evidence from Histological and Isotopic Studies

    Christian Schlechtriem
    The free-living nematode Panagrellus redivivus is a potential source of live food for first feeding fish. The digestion and assimilation of nematodes by larval fish were investigated with the aid of a histological and stable isotope approach. Larvae of whitefish Coregonus lavaretus were reared for 8 d with nematodes and compared with an unfed control. Nematodes were readily ingested by 3-d-old larvae. Different stages of nematode digestion could be observed in transverse sections of fish larvae sampled on Day 6 at regular intervals after feeding. Nematodes were produced on corn medium. In this way nematodes with a stable carbon isotope signature clearly different from the isotopic pattern of the fish larvae could be obtained. Stable carbon isotope signatures for lipids and lipid-free matter of fish larvae sampled on Days 2 and 8 after first feeding were clearly influenced by the stable isotopic pattern of the nematodes. The high acceptance of the nematodes by Coregonus lavaretus larvae and the early onset of digestion and nutrient retention positively confirm the potential of PanagreUus redivivus as a live food for first feeding fish larvae. [source]

    Unemployment and Earnings Assimilation of Immigrants

    LABOUR, Issue 3 2002
    Pål Longva
    The regional unemployment elasticity of annual earnings for non-OECD immigrants is found to be more than three times larger than for natives, using micro data covering all immigrants in Norway in 1990 and a random sample of natives. The decline in relative earnings of non-OECD immigrants from 1980 to 1990 can largely be explained by the stronger impact of rising unemployment on immigrant earnings. These results highlight the importance of controlling for different period effects caused by fluctuating unemployment in panel studies of earnings assimilation among immigrants. [source]

    Assimilation of radar reflectivity into the LM COSMO model with a high horizontal resolution

    Z. Sokol
    Abstract An assimilation of radar reflectivity into a numerical weather prediction (NWP) model with a horizontal resolution of 2.8 km is presented and applied to three severe convective events. The suggested assimilation method takes into account differences between the model and radar-derived precipitation in modifying vertical profiles of water vapour mixing ratio in each model time step by the nudging approach. Version 3.9 of the LM COSMO (Local Model COSMO) ,NWP model used in this study includes the explicit formulation of the cloud and rain processes involved. Two variants of the assimilation technique are designed and outputs of their implementation are compared. The first variant makes use of the ground data only, while the second utilises vertical profiles of precipitation water. Both variants provide an improvement of precipitation forecast in comparison with outputs of the control run without assimilation procedures applied. When the assimilated radar data indicate initial precipitation near an expected storm, the NWP model is capable of forecasting basic features of the storm development two to three hours ahead. Three case studies are presented. In one, the assimilation method that takes into account the vertical structure of the precipitation water yields better results than the others which utilise ground data only. However, for the remaining two case studies both types of the assimilation method produce comparable results. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Assimilation of NAD+ precursors in Candida glabrata

    Biao Ma
    Summary The yeast pathogen Candida glabrata is a nicotinamide adenine dinucleotide (NAD+) auxotroph and its growth depends on the environmental supply of vitamin precursors of NAD+. C. glabrata salvage pathways defined in this article allow NAD+ to be synthesized from three compounds , nicotinic acid (NA), nicotinamide (NAM) and nicotinamide riboside (NR). NA is salvaged through a functional Preiss,Handler pathway. NAM is first converted to NA by nicotinamidase and then salvaged by the Preiss,Handler pathway. Salvage of NR in C. glabrata occurs via two routes. The first, in which NR is phosphorylated by the NR kinase Nrk1, is independent of the Preiss,Handler pathway. The second is a novel pathway in which NR is degraded by the nucleosidases Pnp1 and Urh1, with a minor role for Meu1, and ultimately converted to NAD+ via the nicotinamidase Pnc1 and the Preiss,Handler pathway. Using C. glabrata mutants whose growth depends exclusively on the external NA or NR supply, we also show that C. glabrata utilizes NR and to a lesser extent NA as NAD+ sources during disseminated infection. [source]

    An observing-system experiment with ground-based GPS zenith total delay data using HIRLAM 3D-Var in the absence of satellite data

    Reima Eresmaa
    Abstract Ground-based receiver networks of the Global Positioning System (GPS) provide observations of atmospheric water vapour with a high temporal and horizontal resolution. Variational data assimilation allows researchers to make use of zenith total delay (ZTD) observations, which comprise the atmospheric effects on microwave signal propagation. An observing-system experiment (OSE) is performed to demonstrate the impact of GPS ZTD observations on the output of the High Resolution Limited Area Model (HIRLAM). The GPS ZTD observations for the OSE are provided by the EUMETNET GPS Water Vapour Programme, and they are assimilated using three-dimensional variational data assimilation (3D-Var). The OSE covers a five-week period during the late summer of 2008. In parallel with GPS ZTD data assimilation in the regular mode, the impact of a static bias-correction algorithm for the GPS ZTD data is also assessed. Assimilation of GPS ZTD data, without bias correction of any kind, results in a systematic increase in the forecast water-vapour content, temperature and tropospheric relative topography. A slightly positive impact is shown in terms of decreased forecast-error standard deviation of lower and middle tropospheric humidity and lower tropospheric geopotential height. Moreover, verification of categorical forecasts of 12 h accumulated precipitation shows a positive impact. The application of the static bias-correction scheme is positively verified in the case of the mean forecast error of lower tropospheric humidity and when relatively high precipitation accumulations are considered. Copyright © 2010 Royal Meteorological Society [source]

    Assimilation of satellite-derived soil moisture from ASCAT in a limited-area NWP model

    Jean-François Mahfouf
    Abstract A simplified Extended Kalman Filter is developed for the assimilation of satellite-derived surface soil moisture from the Advanced Scatterometer (ASCAT) instrument (on board the polar-orbiting satellite METOP) in a limited-area NWP model where soil water vertical transfers are described by a force,restore method. An analytic formulation of the land surface scheme Jacobians is derived to simplify the coupling between land surface and atmospheric data assimilation systems. Various steps necessary before the assimilation of ASCAT products are defined: projection of satellite data on the model grid, screening based on various criteria, bias correction using a CDF matching technique, and specification of model and observation errors. Three-dimensional variational data assimilation experiments are then performed during a four-week period in May 2009 over western Europe. A control assimilation is also run where the soil moisture evolves freely. Forecasts from these analyses show that the assimilation of ASCAT data slightly reduces the daytime low-level relative humidity positive bias of the control run. Forecast skill scores with respect to other variables are rather neutral. A comparison of the control run with the operational system where soil moisture is corrected from short-range forecast errors of screen-level observations show similar improvements but are more pronounced. These differences come from the fact that the number of screen-level observations from the surface network over Europe is significantly larger than those provided by a polar-orbiting satellite. These results are consistent with those obtained at ECMWF using soil moisture products derived from other satellite instruments (X-band radiometer TMI and C-band scatterometer ERS). Several avenues for improving this preliminary methodology are proposed. Copyright © 2010 Royal Meteorological Society [source]

    Assimilation of SEVIRI infrared radiances with HIRLAM 4D-Var

    M. Stengel
    Abstract Four-dimensional variational data assimilation (4D-Var) systems are ideally suited to obtain the best possible initial model state by utilizing information about the dynamical evolution of the atmospheric state from observations, such as satellite measurements, distributed over a certain period of time. In recent years, 4D-Var systems have been developed for several global and limited-area models. At the same time, spatially and temporally highly resolved satellite observations, as for example performed by the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) on board the Meteosat Second Generation satellites, have become available. Here we demonstrate the benefit of a regional NWP model's analyses and forecasts gained by the assimilation of those radiances. The 4D-Var system of the HIgh Resolution Limited Area Model (HIRLAM) has been adjusted to utilize three of SEVIRI's infrared channels (located around 6.2 µm, 7.3 µm, and 13.4 µm, respectively) under clear-sky and low-level cloud conditions. Extended assimilation and forecast experiments show that the main direct impact of assimilated SEVIRI radiances on the atmospheric analysis were additional tropospheric humidity and wind increments. Forecast verification reveals a positive impact for almost all upper-air variables throughout the troposphere. Largest improvements are found for humidity and geopotential height in the middle troposphere. The observations in regions of low-level clouds provide especially beneficial information to the NWP system, which highlights the importance of satellite observations in cloudy areas for further improvements in the accuracy of weather forecasts. Copyright © 2009 Royal Meteorological Society [source]

    Assimilation of IASI at the Met Office and assessment of its impact through observing system experiments

    F. Hilton
    Abstract Observations from the Infrared Atmospheric Sounding Interferometer (IASI), onboard EUMETSAT's MetOp satellite, have been assimilated at the Met Office in global and regional numerical weather-prediction systems since 27 November 2007. Pre-operational trials of IASI assimilation in the global model during the summer of 2007 delivered a positive impact on forecasts approximately twice as large as that shown by the Atmospheric InfraRed Sounder (AIRS) on the EOS-Aqua satellite. A series of observing system experiments confirmed the relative performance of IASI and AIRS, and showed that impact from IASI is equivalent to a single Advanced Microwave Sounding Unit-A (AMSU-A) combined with a single Microwave Humidity Sounder (MHS). The results of an IASI assimilation trial for the winter of 2007 were consistent with those of the summer trial, although the impact was slightly lower overall. The assessment of impact is strongly dependent on the variables and methods chosen for verification: assimilation trials with the regional model showed similar improvements to the large-scale fields (e.g. mean-sea-level pressure and geopotential height) as seen in the global model, but no forecast impact was seen for variables such as visibility and rain-rate. © Crown Copyright 2009. Reproduced with the permission of the Controller of HMSO. Published by John Wiley & Sons, Ltd. [source]

    Assimilation of radar-derived rain rates into the convective-scale model COSMO-DE at DWD

    K. Stephan
    Abstract To improve very-short-range forecasts particularly in convective situations, a version of the COSMO-Model (formerly known as LM) which simulates deep convection explicitly (horizontal grid length: 2.8 km) has been developed and is now run operationally at DWD. This model uses a prognostic type of precipitation scheme accounting for the horizontal drift of falling hydrometeors. To initialise convective-scale events, the latent heat nudging (LHN) approach has been adopted for the assimilation of surface precipitation rates derived from radar reflectivity data. It is found that a conventional LHN scheme designed for larger-scale models with diagnostic treatment of precipitation does not perform well and leads to strong overestimation of precipitation when applied to the convective-scale model with a prognostic treatment of precipitation. As illustrated here, surface precipitation and vertically integrated latent heating are far less correlated horizontally and temporally in such a model than with diagnostic precipitation, and this implies a violation of the basic assumption of LHN. Several revisions to the LHN scheme have therefore been developed in view of the characteristic model behaviour so as to re-enhance the validity of the basic assumption and to reduce greatly the overestimation of precipitation during assimilation. With the revised scheme, the model is able to simulate the precipitation patterns in good agreement with radar observations during the assimilation and the first hours of the forecast. The scheme also has a positive impact on screen-level parameters and on the longer-term climatology of the model. Extending the temporal impact of the radar observations further into the free forecast will be the focus of future research. Copyright © 2008 Royal Meteorological Society [source]

    Three-dimensional variational assimilation of Special Sensor Microwave/Imager data into a mesoscale weather-prediction model: A case study

    C. Faccani
    Abstract Assimilation of data from the Special Sensor Microwave/Imager (SSM/I) is performed in order to improve the forecast of a heavy-precipitation case (IOP2b, 20,21 September 1999) of the Mesoscale Alpine Programme 1999. The three-dimensional variational data assimilation technique of the MM5 model is used. Either brightness temperatures or precipitable water and surface wind speed are assimilated. The sensitivity of the model to SSM/I data is also tested by selectively excluding SSM/I frequencies and changing the size of the thinning box. All the experiments are performed using the European Center for Medium range Weather Forecasting (ECMWF) analysis on pressure level. The new initial conditions show considerable underestimation of the surface wind component V, and, even more, of the surface water vapour mixing ratio. This last error is partially corrected by assimilation of precipitable water alone, although these data produce a large increase in the mean error of the other surface variables (U, V and T). However, the forecast with this new set of initial conditions shows a good agreement (high correlation coefficient) with the rain gauge observations for the 1 h accumulated precipitation 3 h after the initial time. With a doubled box size, there is low sensitivity to the density of the observations used. In this case, the effect of the SSM/I data is slight, and the rainfall pattern produced is comparable to that obtained without any data assimilation. The model performance is also degraded if the 22 GHz brightness temperatures are removed from the assimilated measurements: the correlation coefficient for the precipitation is lower than in the case where all the frequencies are assimilated, and it decreases over time. In general, the use of precipitable water and surface wind speed affects the early stages (3 h) of the rainfall forecast, reducing the model spin-up. Brightness temperatures affect the forecast at a longer range (10 h). Copyright © 2007 Royal Meteorological Society [source]

    Data assimilation of high-density observations.

    I: Impact on initial conditions for the MAP/SOP IOP2b
    Abstract An attempt is made to evaluate the impact of the data assimilation of high-frequency data on the initial conditions. The data assimilation of all the data available on the Mesoscale Alpine Program archive for a test case is performed using the objective analysis and the Variational Data Assimilation (Var) techniques. The objective analysis is performed using two different schemes: Cressman and multiquadric; 3D-Var is used for the variational analysis. The European Centre for Medium-Range Weather Forecasts analyses are used as first guess, and they are blended together with the observations to generate an improved set of mesoscale initial and boundary conditions for the Intensive Observing Period 2b (17,21 September 1999). A few experiments are performed using the initialization procedure of MM5, the mesoscale model from Penn State University/National Center for Atmospheric Research. The comparison between improved initial conditions and observations shows: (i) the assimilation of the surface and upper-air data has a large positive impact on the initial conditions depending on the technique used for the objective analysis; (ii) a large decrease of the error for the meridional component of the wind V at the initial time is found, if assimilation of three-hourly data is performed by objective analysis; (iii) a comparable improvement of the initial conditions with respect to the objective analysis is found if 3D-Var is used, but a large error is obtained for the V component of the wind. Copyright © 2005 Royal Meteorological Society [source]

    Assimilation of Meteosat radiance data within the 4D-Var system at ECMWF: Assimilation experiments and forecast impact

    Christina Köpken
    Abstract The direct assimilation of water vapour (WV) clear-sky radiances (CSRs) from geostationary satellites within the ECMWF four-dimensional variational assimilation (4D-Var) became operational on 9 April 2002 with the assimilation of radiances from Meteosat-7. To extend the coverage provided by geostationary radiances, the derivation of a similar CSR product from the Geostationary Operational Environmental Satellites GOES-W and GOES-E was initiated and since 14 January 2003 these data have been operationally assimilated as well. This paper discusses results from the pre-operational impact experiments using Meteosat-7 and the subsequent operational implementation of the WV radiance assimilation. The pre-operational data monitoring of the CSRs shows contamination of certain time slots caused by intruding solar stray light and a certain degree of cloud influence present in the CSR. Data quality control is introduced to exclude affected data. When assimilated, the Meteosat WV CSRs correct the upper-tropospheric humidity field in areas of known model problems. While the analysis draws well to Meteosat data, the fit to other conventional observations does not degrade, and the fit to other satellite observations is noticeably improved. This is visible in statistics for the assimilated HIRS-12 as well as for passive Advanced Microwave Sounding Unit B (AMSUB) radiances, both in the pre-operational experiments and in the operational assimilation cycle. The impact on forecast quality is slightly positive to neutral for different areas of the globe. In some experiments a positive impact on upper-level wind fields (around 200 hPa) is seen, especially in the tropics. A relatively large sensitivity is noted of the mean increments and also forecast scores to the bias correction. Copyright © 2004 Royal Meteorological Society [source]