Rossby wave propagation during winters of maximum frequency of frost occurrence over the wet pampa

Neste trabalho estudou-se a influência dos padrões de onda extratropicais, que favorecem o desenvolvimento de eventos extremos frios no sudeste Sul-Americano, e em particular na região conhecida como Pampa Úmida. O aquecimento anômalo observado na região do oceano Pacífico tropical ocidental a nordeste da Austrália, durante os invernos de máxima freqüência de ocorrência de Geadas Generalizadas (GG) no centro-leste da Argentina, (região conhecida como Pampa Úmida - PU), atua como disparador de ondas de Rossby, as quais se propagam até o continente, favorecendo assim a ocorrência daqueles eventos. O padrão de propagação obtido nas simulações numéricas com um modelo baroclínico global, mostra o predomínio de um número de onda 3. Adicionalmente, foram analisadas as correlações do vento meridional em altos e baixos níveis observados para os eventos de GG, selecionados dentro dos invernos de máxima freqüência de ocorrência desses eventos. O vento meridional global em 250hPa apresenta regiões com correlação estatisticamente significativa com o vento meridional médio na PU. A configuração obtida no caso do vento meridional global em 250hPa, correlacionado com o vento meridional na PU, pode estar associada ao padrão de propagação das ondas simuladas numericamente a partir da forçante tropical. Igualmente importantes e significativos são os valores de correlação do vento sul nos baixos níveis, em particular para toda região da PU. O padrão de ondas simulado está bem representado pelas significativas correlações entre o vento meridional hemisférico em altos níveis e a temperatura no dia de evento de GG.The influence of extratropical waves on the development of extreme cold events over southeast South America, particularly on the Argentinean Wet Pampa region is studied in this work. An anomalous heating observed over the occidental tropical Pacific Ocean, northeast of Australia, during Austral winters of maximum frequency of Generalized Frost (GF) occurrence over the center-east of Argentina, known as Wet Pampa (WP), acts as a Rossby wave source which generate waves that propagate towards the South American continent favoring the frost events. The wave propagation pattern obtained from simulations using a Global Baroclinic Model shows wavenumber 3 dominance. Additional, upper and lower levels meridional wind correlations during the GF events selected were analyzed. The 250hPa global meridional wind shows a significant correlation (0.9) with the meridional wind at the WP region. The wave propagation pattern observed in this case agrees with that simulated by the model when a heating source is located at the Pacific tropical ocean. Also, significant correlation values were found for the low level southern winds at the WP region. The wave pattern simulated shows a good correlation between the hemispheric meridional wind at higher levels and the air temperature in the day of GF events.Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET

Observed and projected changes in temperature and precipitation in the core crop region of the humid pampa, Argentina

The core crop region of the Humid Pampa is one of the most productive agricultural lands around the world and depends highly on climate conditions. This study assesses climate variability, climate extremes, and observed and projected climate changes there, using 1911–2019 observations and CMIP5 model simulations. Since 1970, the annual mean temperature has risen by 1 °C and the mean annual minimum and maximum temperatures by 2 and 0.5 °C, respectively. The frequency of warm days and nights increased, and cold days and nights decreased. Heatwaves became longer and more intense, and cold waves decreased with less frost events. Annual precipitation increased by 10% from 1911, mainly in summer, and years with excess precipitation outnumbered those with a deficit. Both intense precipitation events and consecutive dry days grew, suggesting more annual precipitation falling on fewer days. Projections show a warming of 1 ºC by 2035, regardless of the scenario. From then on until 2100, mean temperature will increase by 2 and 3–3.5 °C in the RCP4.5 and RCP8.5 scenarios, respectively. Annual precipitation will grow 8 and 16% from current values by 2100 in the RCP4.5 and RCP8.5 scenarios, respectively. No major precipitation changes are projected in the RCP2.6 scenario.Fil: Müller, Gabriela V.. Universidad Nacional del Litoral. Facultad de Ingenieria y Ciencias Hidricas. Centro de Estudios de Variabilidad y Cambio Climatico.; ArgentinaFil: Lovino, Miguel Angel. Universidad Nacional del Litoral. Facultad de Ingenieria y Ciencias Hidricas. Centro de Estudios de Variabilidad y Cambio Climatico.; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Sgroi, Leandro Carlos. Universidad Nacional del Litoral. Facultad de Ingenieria y Ciencias Hidricas. Centro de Estudios de Variabilidad y Cambio Climatico.; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentin

Interannual-to-multidecadal Hydroclimate Variability and its Sectoral Impacts in northeastern Argentina

This study examines the joint variability of pre- cipitation, river streamflow and temperature over northeast- ern Argentina; advances the understanding of their links with global SST forcing; and discusses their impacts on water re- sources, agriculture and human settlements. The leading pat- terns of variability, and their nonlinear trends and cycles are identified by means of a principal component analysis (PCA)complemented with a singular spectrum analysis (SSA). In- terannual hydroclimatic variability centers on two broad fre- quency bands: one of 2.5?6.5 years corresponding to El Niño Southern Oscillation (ENSO) periodicities and the second of about 9 years. The higher frequencies of the precipita- tion variability (2.5?4 years) favored extreme events after 2000, even during moderate extreme phases of the ENSO. Minimum temperature is correlated with ENSO with a main frequency close to 3 years. Maximum temperature time se- ries correlate well with SST variability over the South At- lantic, Indian and Pacific oceans with a 9-year frequency. Interdecadal variability is characterized by low-frequency trends and multidecadal oscillations that have induced a tran- sition from dryer and cooler climate to wetter and warmer decades starting in the mid-twentieth century. The Paraná River streamflow is influenced by North and South Atlantic SSTs with bidecadal periodicities.The hydroclimate variability at all timescales had signif- icant sectoral impacts. Frequent wet events between 1970 and 2005 favored floods that affected agricultural and live- stock productivity and forced population displacements. On the other hand, agricultural droughts resulted in soil mois- ture deficits that affected crops at critical growth stages. Hy-drological droughts affected surface water resources, caus- ing water and food scarcity and stressing the capacity for hydropower generation. Lastly, increases in minimum tem- perature reduced wheat and barley yields.Fil: Lovino, Miguel Angel. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Müller, Omar Vicente. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas; ArgentinaFil: Müller, Gabriela V.. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas; ArgentinaFil: Sgroi, Leandro Carlos. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas; ArgentinaFil: Baethgen, Walter. Columbia University; Estados Unido

Variability and changes of daily climate extremes over the core crop region of Argentina

Ponencia presentada en: XI Congreso de la Asociación Española de Climatología celebrado en Cartagena entre el 17 y el 19 de octubre de 2018.[ES]La variabilidad y los cambios en extremos climáticos afectan la región núcleo de cultivos de Argentina y pueden incrementar su vulnerabilidad ocasionando desastres sin precedentes. Este estudio investiga los cambios de largo período y la variabilidad interanual de los extremos climáticos diarios de precipitación y temperatura y evalúa en qué medida los reanálisis globales reproducen la variabilidad observada en el pasado reciente. Los datos incluyen observaciones con calidad controlada (1963-2013) y los reanálisis ERA-Interim y NCEP2 (1979-2011). Los extremos climáticos se caracterizan espacial y temporalmente con 11 índices de los propuestos por el Equipo de Expertos sobre Detección e Índices de Cambio Climático. Se aplicó un Análisis Espectral Singular para detectar los modos principales de las series temporales medias areales de los índices. Se ajustaron tendencias no-paramétricas lineales a las series temporales de cada índice para estimar la distribución espacial de los cambios medios. Los extremos de temperatura están cambiando hacia condiciones más cálidas. Los días cálidos han estado aumentando desde 1990 mientras que los días fríos han ido decreciendo. Las noches cálidas y frías muestran una señal de calentamiento significativa que parece estar estabilizándose en las últimas décadas. Los eventos de precipitación intensa aumentaron constantemente en la mayor parte de la región desde 1970. La cantidad máxima anual de precipitación en un día aumentó desde la década de 1970 hasta la del 2000, estabilizándose en años recientes. El reanálisis ERA-Interim puede reconocer los extremos de temperatura en tiempo y en espacio, mientras que el antiguo NCEP2 presenta errores sistemáticos. Ambos reanálisis reproducen la máxima precipitación anual en 5 días con grandes sesgos. Aunque se esperaría que los reanálisis agreguen información para extremos climáticos en áreas de observaciones escasas, aún deben usarse con mucha precaución y solo como complemento de las observaciones.[EN]Variability and changes in climate extremes affect the core crop region of Argentina and may increase its vulnerability leading to unprecedented disasters. This study investigates the long-term changes and interannual variability of daily temperature and precipitation climate extremes and assesses to what extent global reanalyses reproduce the observed variability in the recent past. Datasets include quality-controlled observations (1963-2013) and ERA-Interim and NCEP2 reanalyses (1979-2011). Climate extremes are characterized spatially and temporally by 11 indices proposed by the Expert Team on Climate Change Detection and Indices. A Singular Spectrum Analysis was applied to detect the leading modes of the area-averaged index time series. Nonparametric linear trends were fitted to each index time series to estimate the spatial distribution of mean changes. Temperature extremes are changing towards warmer conditions. Warm days has been increasing since 1990 while cold days has been decreasing. Warm and cold nights show a significant signal of warming that seems to be stabilizing in recent decades. Intense precipitation events in most of the region increased steadily since 1970. The annual maximum amount of 1-day precipitation events increased from the 1970s to the 2000s, stabilizing in recent years. The ERA-Interim reanalysis can recognize temperature extremes in time and space, while the older NCEP2 presents systematic biases. Both reanalyses reproduce the annual maximum 5-day precipitation with large biases. Although reanalyses would be expected to add information for climate extremes in areas of scarce observations, they still need to be used with great caution and only as a complement to observations.We appreciate the grant from the PRODACT 2018 of the Science and Technical Secretariat (FICH UNL). This research was carried out with support of Projects CRN3035 and CRN3095 of the Inter-American Institute for Global Change Research (IAI), which is supported by the US National Science Foundation. UNL Project C.A.I. + D. 2016 32/180 is also acknowledged

Future projections of extreme cold events in southeastern southamerica as reproduced by HadCM3 model

Las simulaciones del modelo HadCM3 fueron de las primeras disponibles para el análisis de proyecciones futuras, reflejándose en la literatura que describe principalmente variables de temperatura y precipitación para Sudamérica. El objetivo de ese trabajo es investigar los cambios en la circulación atmosférica en el sudeste de Sudamérica asociada a eventos extremos fríos, en el escenario de emisiones futuras más crítico denominado A2, para el periodo 2081-2100 respecto a un periodo climatológico de referencia 1961-1990, considerando el modelo HadCM3 y los datos del reanálisis NCEP/NCAR. A partir de la temperatura media diaria en 850 hPa, se identifican los eventos de temperatura negativa para los meses de mayo a septiembre, componiéndose los cinco eventos más extremos para tres áreas que incluyen la Pampa Húmeda (área 1), Uruguay y sur de Brasil (área 2), la parte oriental de Paraguay, norte de Argentina y sur de Brasil (área 3).Los patrones de circulación son analizados tanto para el reanálisis como para las simulaciones en el clima presente y futuro. Los resultados muestran para el clima presente que el modelo simula la incursión de las isotermas de 0°C más al norte respecto del reanálisis, a excepción del área 3 que limita con los trópicos, con anomalías negativas de temperatura más intensas y más extensas en términos latitudinales. A pesar que las configuraciones de los campos de presión sean similaresal reanálisis, se aprecia una mayor penetración del anticiclón continental, a excepción del área 3, con una intensificación de las anomalías en las respectivas áreas. El modelo también tiende a simular una componente de viento del sur más intensa en 850 hPa y captura la profunda vaguada sobre el continente en niveles altos con el jet subtropical bien configurado, típico de estos eventos extremos. En el escenario futuro, el modelo no proyecta eventos extremos de temperatura por debajo de 0°C para el área 3, restringiendo la incursión de la isoterma de 0° C a latitudes más al sur en las otras dos áreas respecto a la simulación en el clima presente, en concordancia con el aumento de temperatura media que el modelo proyecta para Sudamérica.The simulations with the HadCM3 model were among the first available to analyze future projections. This is reflected in the literature, which mainly describes the variables temperature and precipitation for South America. The aim of this paper is to investigate the changes in the atmospheric circulation over southeastern South America associated to extreme cold events in the most critical future emission scenario A2 for the period 2081-2100, with respect to the climatological reference period 1961-1990. To do that the HadCM3 model is used as well as the NCEP/NCAR reanalysis. Were identified the five most extreme events of daily mean negative temperature in 850 hPa from May to September over three areas: Wet Pampa (area 1), Uruguay and southern Brazil (area 2), eastern Paraguay, northern Argentina and southern Brazil (area 3). The obtained circulation patterns are analyzed in both, the reanalysis and the HadCM3 simulations of the present and future climate. In the present climate, with the exception of the area 3 that borders the tropics, the model simulates a more extended northward incursion of the 0oC isotherm than the reanalysis. It also shows more intense negative temperature anomalies, which have more latitudinal extension. Despite the fact that the configurations of the pressure fields are similar to that of the reanalysis, except for the area 3, a further inland penetration of the continental anticyclone is appreciated, with an intensification of the anomalies over the respective areas. The model also tends to simulate a more intense 850 hPa southerly wind component, capturing the high level deep trough over the continent and displaying a properly configured subtropical jet, which is typical of these extreme events. In the future scenario, the model does not project extreme cold events of below 0oC temperatures for area 3. The model also restricts the incursion of the 0oC isotherm to more southerly latitudes in the other two areas with respect to the simulation of the present climate. These facts are consistent with the mean temperature increase projected by the model for South America.Fil: Müller, Gabriela V.. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; ArgentinaFil: Rabelo Da Rocha Repinaldo, Cintia. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; ArgentinaFil: Andrade, Kelen M.. Centro de Previsao de Tempo e Estudos Climáticos. Instituto Nacional de Pesquisas Espaciais; BrasilFil: Cavalcanti, Iracema F. A.. Centro de Previsao de Tempo e Estudos Climáticos. Instituto Nacional de Pesquisas Espaciais; Brasi

Comparison between circulation patterns associated to frost events in the humid pampa in climatic settings related with the experiments CMIP3 and CMIP5 of the GFDL model

El propósito de este estudio es investigar los cambios en la circulación atmosférica asociados a eventos de heladas en la Pampa Húmeda (PH) en el clima futuro para los escenarios más críticos proyectados por el modelo acoplado oceano-atmósfera GFDL. Se emplea el modelo GFDL en sus dos versiones (GFDL-CM2 para el CMIP3 y GFDL-CM3 para el CMIP5). Se analiza la capacidad del modelo para simular los cinco eventos extremos más fríos en el clima presente (1961-1990), respecto de los obtenidos en el reanálisis del NCEP/NCAR. Luego se comparan las simulaciones del clima futuro (2081-2100) con las del presente. En el experimento CMIP3 del clima presente el modelo muestra una mayor penetración de la isoterma de 0°C en 850 hPa, con anomalías de temperatura negativas más intensas que las del NCEP. El anticiclón pos frontal se observa más extendido meridionalmente sobre el continente, con valores de anomalías similares principalmente en la Pampa Húmeda. El gradiente de presión entre la alta y la baja corriente abajo, provoca un flujo de aire frio del sur más intenso en 850 hPa que en el reanálisis, propiciando heladas del tipo advectivas en la región de estudio. En el clima futuro el modelo proyecta una menor incursión de la isoterma de 0°C y con anomalías negativas de temperatura más pequeñas. El máximo del anticiclón en el futuro se localiza más al norte que en el presente, propiciando heladas del tipo radiativas. En el campo de altura, el jet subtropical se presenta más zonal y con intensidades ligeramente mayores que en las simulaciones del clima presente. Para el experimento CMIP5 en el clima presente el modelo logra simular la incursión de la isoterma de 0°C, pero la anomalía de temperatura es mayor que en el reanálisis. El campo de presión presenta similares características que en el experimento de CMIP3, pero con anomalías más intensas al sur del continente. En el escenario futuro el modelo proyecta la incursión de la isoterma de 0°C, así como la anomalía negativa de temperatura, similares al presente. El anticiclón pos frontal se localiza más al norte, sobrestimando tanto su valor así como su anomalía en la PH. El campo de viento no muestra diferencias respecto del presente. En suma, comparando los dos experimentos, el de CMIP3 en el futuro muestra importantes cambios respecto al presente, lo que no ocurre en el CMIP5. Esos cambios se ven principalmente en el campo de presión, donde para el CMIP3 (CMIP5) las heladas tipo radiativas (advectivas) serían las favorecidas en la Pampa Húmeda debido a la posición del anticiclón.The purpose of this study is to investigate the change in the atmospheric circulation associated with frost events in the Wet Pampa (WP) in the future climate for the most critical scenarios projected by the GFDL ocean-atmosphere coupled model. Two versions of the GFDL model are used, the GFDL-CM2 for CMIP3 and GFDL-CM3 for CMIP5. We analyze the model capability to simulate the five most extreme cold events in the present climate (1961-1990), with respect to those obtained with the NCEP/NCAR Reanalysis. Then, we compare the future climate simulations (2081-2100) with the model simulation for the present climate. For the present climate the CMIP3 experiment presents more penetration of the 0°C isotherm in 850 hPa, intensifying the negative temperature anomalies in comparison to the reanalysis. The postfrontal anticyclone is more meridionally extended over the continent, with similar anomalies to those of the reanalysis, mainly over WP. The gradient between the high pressure and the low pressure downwind creates a more intense southerly cold airflow at 850 hPa than the reanalysis, giving place to advective frosts in the studied region. For the future climate, the model projects less penetration of the 0°C isotherm and less intense negative temperature anomalies. The anticyclone maximum is located further north than in the present climate, propitiating radiative frosts. In the upper levels, the subtropical jet shows a more zonally layout and slightly higher intensity than in the present climate simulations. For the present climate the CMIP5 experiment simulates well the incursion of the 0°C isotherm, although with a more intense temperature anomaly in comparison to the reanalysis. The pressure field presents similar characteristics to those shown in the CMIP3 experiment, but with larger anomalies in the southern part of the continent. For the future scenario, the model projects the 0°C isotherm incursion as well as the negative temperature anomalies similar to the present. The post frontal anticyclone is located further north, overestimating its value and the anomaly over WP. The wind field is similar to the present simulation. Summarizing the results of both experiments, the future projections with CMIP3 show significant changes with respect to the present, which is not the case with the CMIP5 experiment. These changes are mainly reflected in the pressure field, in which the position of the anticyclone in CMIP3 (CMIP5) would favor radiative (advective) frosts over WP.Asociación Argentina de Geofísicos y Geodesta

Dengue emergence in the temperate Argentinian province of Santa Fe, 2009–2020

Dengue virus (DENV) transmission occurs primarily in tropical and subtropical climates, but within the last decade it has extended to temperate regions. Santa Fe, a temperate province in Argentina, has experienced an increase in dengue cases and virus circulation since 2009, with the recent 2020 outbreak being the largest in the province to date. The aim of this work is to describe spatio-temporal fluctuations of dengue cases from 2009 to 2020 in Santa Fe Province. The data presented in this work provide a detailed description of DENV transmission for Santa Fe Province by department. These data are useful to assist in investigating drivers of dengue emergence in Santa Fe Province and for developing a better understanding of the drivers and the impacts of ongoing dengue emergence in temperate regions across the world. This work provides data useful for future studies including those investigating socio-ecological, climatic, and environmental factors associated with DENV transmission, as well as those investigating other variables related to the biology and the ecology of vector-borne diseases.Fil: López, María S.. Universidad Nacional del Litoral. Facultad de Ingenieria y Ciencias Hidricas. Centro de Estudios de Variabilidad y Cambio Climatico.; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Centro de Investigaciones sobre Endemias Nacionales; ArgentinaFil: Jordan, Daniela I.. Ministerio de Salud de la Provincia de Santa Fe; ArgentinaFil: Blatter, Evelyn. Universidad Nacional del Litoral. Facultad de Ingenieria y Ciencias Hidricas. Centro de Estudios de Variabilidad y Cambio Climatico.; ArgentinaFil: Walker, Elisabet. Universidad Nacional del Litoral. Facultad de Ingenieria y Ciencias Hidricas. Centro de Estudios de Variabilidad y Cambio Climatico.; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Gomez, Andrea Alejandra. Universidad Nacional del Litoral. Facultad de Ingenieria y Ciencias Hidricas. Centro de Estudios de Variabilidad y Cambio Climatico.; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Müller, Gabriela V.. Universidad Nacional del Litoral. Facultad de Ingenieria y Ciencias Hidricas. Centro de Estudios de Variabilidad y Cambio Climatico.; ArgentinaFil: Mendicino, Diego Antonio. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Centro de Investigaciones sobre Endemias Nacionales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Robert, Michael A.. Virginia Commonwealth University; Estados UnidosFil: Estallo, Elizabet Lilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentin

Towards a leptospirosis early warning system in northeastern Argentina

Leptospirosis is a zoonotic disease with a high burden in Latin America, including northeastern Argentina, where flooding events linked to El Niño are associated with leptospirosis outbreaks. The aim of this study was to evaluate the value of using hydrometeorological indicators to predict leptospirosis outbreaks in this region. We quantified the effects of El Niño, precipitation, and river height on leptospirosis risk in Santa Fe and Entre Ríos provinces between 2009 and 2020, using a Bayesian modelling framework. Based on several goodness of fit statistics, we selected candidate models using a long-lead El Niño 3.4 index and shorter lead local climate variables. We then tested predictive performance to detect leptospirosis outbreaks using a two-stage early warning approach. Three-month lagged Niño 3.4 index and one-month lagged precipitation and river height were positively associated with an increase in leptospirosis cases in both provinces. El Niño models correctly detected 89% of outbreaks, while short-lead local models gave similar detection rates with a lower number of false positives. Our results show that climatic events are strong drivers of leptospirosis incidence in northeastern Argentina. Therefore, a leptospirosis outbreak prediction tool driven by hydrometeorological indicators could form part of an early warning and response system in the region

Searching for a Stochastic Background of Gravitational Waves with LIGO

The Laser Interferometer Gravitational-wave Observatory (LIGO) has performed the fourth science run, S4, with significantly improved interferometer sensitivities with respect to previous runs. Using data acquired during this science run, we place a limit on the amplitude of a stochastic background of gravitational waves. For a frequency independent spectrum, the new limit is $\Omega_{\rm GW} < 6.5 \times 10^{-5}$. This is currently the most sensitive result in the frequency range 51-150 Hz, with a factor of 13 improvement over the previous LIGO result. We discuss complementarity of the new result with other constraints on a stochastic background of gravitational waves, and we investigate implications of the new result for different models of this background.Comment: 37 pages, 16 figure

Quantum state preparation and macroscopic entanglement in gravitational-wave detectors

Long-baseline laser-interferometer gravitational-wave detectors are operating at a factor of 10 (in amplitude) above the standard quantum limit (SQL) within a broad frequency band. Such a low classical noise budget has already allowed the creation of a controlled 2.7 kg macroscopic oscillator with an effective eigenfrequency of 150 Hz and an occupation number of 200. This result, along with the prospect for further improvements, heralds the new possibility of experimentally probing macroscopic quantum mechanics (MQM) - quantum mechanical behavior of objects in the realm of everyday experience - using gravitational-wave detectors. In this paper, we provide the mathematical foundation for the first step of a MQM experiment: the preparation of a macroscopic test mass into a nearly minimum-Heisenberg-limited Gaussian quantum state, which is possible if the interferometer's classical noise beats the SQL in a broad frequency band. Our formalism, based on Wiener filtering, allows a straightforward conversion from the classical noise budget of a laser interferometer, in terms of noise spectra, into the strategy for quantum state preparation, and the quality of the prepared state. Using this formalism, we consider how Gaussian entanglement can be built among two macroscopic test masses, and the performance of the planned Advanced LIGO interferometers in quantum-state preparation