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Showing papers in "Journal of Climate in 1996"


Journal ArticleDOI
TL;DR: In this paper, a revised version of the Simple Biosphere model (SiB2) is presented, incorporating a realistic canopy photosynthesis-conductance model to describe the simultaneous transfer of CO2 and water vapor into and out of the vegetation, respectively.
Abstract: The formulation of a revised land surface parameterization for use within atmospheric general circulation models (GCMs) is presented. The model (SiB2) incorporates several significant improvements over the first version of the Simple Biosphere model (SiB) described in Sellers et al. The improvements can be summarized as follows: (i) incorporation of a realistic canopy photosynthesis–conductance model to describe the simultaneous transfer of CO2 and water vapor into and out of the vegetation, respectively; (ii) use of satellite data, as described in a companion paper, Part II, to describe the vegetation phonology; (iii) modification of the hydrological submodel to give better descriptions of baseflows and a more reliable calculation of interlayer exchanges within the soil profile; (iv) incorporation of a “patchy” snowmelt treatment, which prevents rapid thermal and surface reflectance transitions when the area-averaged snow cover is low and decreasing. To accommodate the changes in (i) and (ii) ab...

1,861 citations


Journal ArticleDOI
TL;DR: In this paper, an algorithm is developed to construct global gridded fields of monthly precipitation by merging estimates from five sources of information with different characteristics, including gauge-based monthly analyses from the Global Precipitation Climatology Centre, three types of satellite estimates [the infrared-based GOES precipitation index, the microwave (MW) scattering-based Grody, and the MW emission-based Chang estimates], and predictions produced by the operational forecast model of the European Centre for Medium-Range Weather Forecasts.
Abstract: An algorithm is developed to construct global gridded fields of monthly precipitation by merging estimates from five sources of information with different characteristics, including gauge-based monthly analyses from the Global Precipitation Climatology Centre, three types of satellite estimates [the infrared-based GOES Precipitation Index, the microwave (MW) scattering-based Grody, and the MW emission-based Chang estimates], and predictions produced by the operational forecast model of the European Centre for Medium-Range Weather Forecasts. A two-step strategy is used to: 1) reduce the random error found in the individual sources and 2) reduce the bias of the combined analysis. First, the three satellite-based estimates and the model predictions are combined linearly based on a maximum likelihood estimate, in which the weighting coefficients are inversely proportional to the squares of the individual random errors determined by comparison with gauge observations and subjective assumptions. This c...

1,362 citations


Journal ArticleDOI
TL;DR: In this article, the authors used satellite data to specify the time-varying phonological properties of FPAR, leaf area index, and canopy greenness fraction, and applied corrections to the source NDVI dataset to account for anomalies in the data time series, the effect of variations in solar zenith angle, data dropouts in cold regions where a temperature threshold procedure designed to screen for clouds also eliminated cold land surface points, and persistent cloud cover in the Tropics.
Abstract: The global parameter fields used in the revised Simple Biosphere Model (SiB2) of Sellers et al. are reviewed. The most important innovation over the earlier SiB1 parameter set of Dorman and Sellers is the use of satellite data to specify the time-varying phonological properties of FPAR, leaf area index. and canopy greenness fraction. This was done by processing a monthly 1° by 1° normalized difference vegetation index (NDVI) dataset obtained farm Advanced Very High Resolution Radiometer red and near-infrared data. Corrections were applied to the source NDVI dataset to account for (i) obvious anomalies in the data time series, (ii) the effect of variations in solar zenith angle, (iii) data dropouts in cold regions where a temperature threshold procedure designed to screen for clouds also eliminated cold land surface points, and (iv) persistent cloud cover in the Tropics. An outline of the procedures for calculating the land surface parameters from the corrected NDVI dataset is given, and a brief d...

1,174 citations


Journal ArticleDOI
TL;DR: In this article, the development of sea surface temperature (SST) anomaly patterns over the tropical Atlantic was investigated and the evolution of large-scale rainfall anomaly pattern over the equatorial Atlantic and South America were also investigated.
Abstract: Empirical orthogonal functions (E0Fs) and composite analyses are used to investigate the development of sea surface temperature (SST) anomaly patterns over the tropical Atlantic. The evolution of large-scale rainfall anomaly patterns over the equatorial Atlantic and South America are also investigated. The EOF analyses revealed that a pattern of anomalous SST and wind stress asymmetric relative to the equator is the dominant mode of interannual and longer variability over the tropical Atlantic. The most important findings of this study are as follows. Atmospheric circulation anomalies precede the development of basinwide anomalous SST patterns over the tropical Atlantic. Anomalous SST originate off the African coast simultaneously with atmospheric circulation anomalies and expand westward afterward. The time lag between wind stress relaxation (strengthening) and maximum SST warming (cooling) is about two months. Anomalous atmospheric circulation patterns over northern tropical Atlantic are phase ...

819 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe the Arctic temperature and humidity characteristics, cloud properties and processes, radiative characteristics of the atmosphere and surface, direct and indirect radiative effects of aerosols, and the modeling and satellite remote sensing of cloud and radiative properties.
Abstract: To provide a background for ARM's activities at the North Slope of Alaska/Adjacent Arctic Ocean sites, an overview is given of our current state of knowledge of Arctic cloud and radiation properties and processes. The authors describe the Arctic temperature and humidity characteristics, cloud properties and processes, radiative characteristics of the atmosphere and surface, direct and indirect radiative effects of aerosols, and the modeling and satellite remote sensing of cloud and radiative characteristics. An assessment is given of the current performance of satellite remote sensing and climate modeling in the Arctic as related to cloud and radiation issues. Radiation-climate feedback processes are discussed, and estimates are made of the sign and magnitude of the individual feedback components. Future plans to address these issues are described.

771 citations


Journal ArticleDOI
TL;DR: In this article, the onset and interannual variability of the Asian summer monsoon in relation to land-sea thermal contrast and its contributing factors are studied using a 14-yr (1979-1992) dataset.
Abstract: The onset and interannual variability of the Asian summer monsoon in relation to land–sea thermal contrast and its contributing factors are studied using a 14-yr (1979–1992) dataset. The onset of the Asian summer monsoon is concurrent with the reversal of meridional temperature gradient in the upper troposphere south of the Tibetan Plateau. The reversal is the result of large temperature increases in May to June over Eurasia centered on the Plateau with no appreciable temperature change over the Indian Ocean. In spring the Tibetan Plateau is a heat source that is distinctly separate from the heat source associated with the rain belt in the equatorial Indian ocean. The Tibetan heat source is mainly contributed by sensible heat flux from the ground surface, while the oceanic heat source is due to the release of latent heat of condensation. It is the sensible heating over the Plateau region in spring that leads to the reversal of meridional temperature gradient. Despite its intensity the condensatio...

733 citations


Journal ArticleDOI
TL;DR: In this article, a principal component analysis (PCA) was used to improve the accuracy of the NCDC's optimum interpolation (OI) analysis of sea surface temperature (SST) from 1950 to 1981.
Abstract: Studies of climate variability often rely on high quality sea surface temperature (SST) anomalies. Although the high-resolution National Centers for Environmental Prediction (formerly the National Meteorological Center) optimum interpolation (OI) SST analysis is satisfactory for these studies, the OI resolution cannot be maintained before November 1931 due to the lack of satellite data. Longer periods of SSTs have come from traditional analyses of in situ (ship and buoy) SST observations alone. A new interpolation method is developed using spatial patterns from empirical orthogonal functions (E0Fs)—that is, a principal component analysis—to improve analyses of SST anomalies from 1950 to 1981. The method uses the more accurate OI analyses from 1982 to 1993 to produce the spatial EOFs. The dominant EOF modes (which correspond to the largest variance) are used as basis functions and are fit, in a least squares sense, to the in situ data to determine the time dependence of each mode. A complete field...

643 citations


Journal ArticleDOI
Qiang Fu1
TL;DR: In this article, the extinction coefficient, absorption coefficient, and asymmetry factor are parameterized as functions of the cloud ice water content and generalized effective size, and validated by examining the bulk radiative properties for a wide range of atmospheric conditions.
Abstract: An accurate parameterization is presented for the infrared radiative properties of cirrus clouds. For the singlescattering calculations, a composite scheme is developed for randomly oriented hexagonal ice crystals by comparing results from Mie theory, anomalous diffraction theory (ADT), the geometric optics method (GOM), and the finite-difference time domain technique. This scheme employs a linear combination of single-scattering properties from the Mie theory, ADT, and GOM, which is accurate for a wide range of size parameters. Following the approach of Q. Fu, the extinction coefficient, absorption coefficient, and asymmetry factor are parameterized as functions of the cloud ice water content and generalized effective size ( Dge). The present parameterization of the single-scattering properties of cirrus clouds is validated by examining the bulk radiative properties for a wide range of atmospheric conditions. Compared with reference results, the typical relative error in emissivity due to the parameterization is ;2.2%. The accuracy of this parameterization guarantees its reliability in applications to climate models. The present parameterization complements the scheme for the solar radiative properties of cirrus clouds developed by Q. Fu for use in numerical models.

608 citations


Journal ArticleDOI
TL;DR: In this article, a series of earlier studies has identified regions of the world in which precipitation appears to have a consistent relationship with the Southern Oscillation (SO), and the authors attempt to quantify this relationship based on shifts in the statistical distribution of precipitation amounts with emphasis on the median, which are associated with the warm and cold phases of the SO.
Abstract: A series of earlier studies has identified regions of the world in which precipitation appears to have a consistent relationship with the Southern Oscillation (SO). In this paper, the authors attempt to quantify this relationship based on shifts in the statistical distribution of precipitation amounts with emphasis on shifts in the median, which are associated with the warm (low SO index) and cold (high SO index) phases of the SO. This paper is partially an attempt to provide long-range forecasters with some guidance in making seasonal and multiseasonal predictions. Observed SO-related shifts in the median precipitation amounts, expressed as percentiles with respect to “climatological” conditions, can he used as a simple indication of the “typical” SO response for a given region. In general, the authors find that for many of the large areas identified in previous studies, median precipitation amounts shift on the order of 20 percentile points, that is, from the median to either the 30th percentil...

570 citations


Journal ArticleDOI
TL;DR: In this paper, the role of ocean dynamics in the regulation of tropical sea surface temperatures (SSTs) was investigated using the Zebiak-Cane coupled occan-atmosphere model.
Abstract: The role of ocean dynamics in the regulation of tropical sea surface temperatures (SSTs) is investigated using the Zebiak-Cane coupled occan-atmosphere model. The model is forced with a uniform heating, or cooling, varying between ±40 W m−2 into the ocean surface. A new climatological SST pattern is established for which the area-averaged temperature change is smaller in magnitude than the imposed forcing. The forcing is balanced almost equally by a change in the heat flux out of the ocean and by vertical advection of heat in the ocean through anomalous equatorial ocean upwelling. The generation of anomalous upwelling is identified here as a possible mechanism capable of regulating tropical SSTS. This ocean dynamical thermostat mechanism has, a seasonally varying efficiency that causes amplification (weakening) of the seasonal cycle for the heating (cooling). The interannual variability also changes under the imposed forcing. These results suggest that the role of ocean dynamic should he included...

548 citations


Journal ArticleDOI
TL;DR: In this article, the dynamics and predictability of decadal climate variability over the North Pacific and North America are investigated by analyzing various observational datasets and the output of a state-of-the-art coupled ocean-atmosphere general circulation model that was integrated for 125 years.
Abstract: The dynamics and predictability of decadal climate variability over the North Pacific and North America are investigated by analyzing various observational datasets and the output of a state of the art coupled ocean–atmosphere general circulation model that was integrated for 125 years. Both the observations and model results support the picture that the decadal variability in the region of interest is based on a cycle involving unstable ocean–atmosphere interactions over the North Pacific. The period of this cycle is of the order of a few decades. The cycle involves the two major circulation regimes in the North Pacific climate system, the subtropical ocean gyre, and the Aleutian low. When, for instance, the subtropical ocean gyre is anomalously strong, more warm tropical waters are transported poleward by the Kuroshio and its extension, leading to a positive SST anomaly in the North Pacific. The atmospheric response to this SST anomaly involves a weakened Aleutian low, and the associated fluxes at the air–sea interface reinforce the initial SST anomaly, so that ocean and atmosphere act as a positive feedback system. The anomalous heat flux, reduced ocean mixing in response to a weakened storm track, and anonmalous Ekman heat transport contribute to this positive feedback. The atmospheric response, however, consists also of a wind stress curl anomaly that spins down the subtropical ocean gyre, thereby reducing the poleward heat transport and the initial SST anomaly. The ocean adjusts with some time lag to the change in the wind stress curl, and it is this transient ocean response that allows continuous oscillations. The transient response can be expressed in terms of baroclinic planetary waves, and the decadal timescale of the oscillation is therefore determined to first order by wave timescales. Advection by the mean currents, however, is not negligible. The existence of such a cycle provides the basis of long-range climate forecasting over North America at decadal timescales. At a minimum, knowledge of the present phase of the decadal mode should allow a “now-cast” of expected climate “bias” over North America, which is equivalent to a climate forecast several years ahead.

Journal ArticleDOI
TL;DR: In this article, the authors found that climate asymmetries are prominent in the eastern tropical Pacific and Atlantic Oceans where the regions of maximum sea surface temperature, convective cloud cover, and rainfall are north of the equator.
Abstract: Although the distribution of sunshine is symmetrical about the equator, the earth's climate is not. Climatic asymmetries are prominent in the eastern tropical Pacific and Atlantic Oceans where the regions of maximum sea surface temperature, convective cloud cover, and rainfall are north of the equator. This is the result of two sets of factors: interactions between the ocean and atmosphere that are capable of converting symmetry into asymmetry, and the geometries of the continents that determine in which longitudes the interactions are effective and in which hemisphere the warmest waters and the intertropical convergence zone are located. 'The Ocean-atmosphere interactions are most effective where the thermocline is shallow because the winds can readily affect sea surface temperatures in such regions. The thermocline happens to shoal in the eastern equatorial Pacific and Atlantic, but not in the eastern Indian Ocean, because easterly trade winds prevail over the tropical Atlantic and Pacific wher...

Journal ArticleDOI
TL;DR: In this paper, the Monte Carlo Singular Systems Analysis (SSA) algorithm is used to identify intermittent or modulated oscillations in geophysical and climatic time series, and the results show that the strength of the evidence provided by SSA for interannual and interdecadal climate oscillations has been considerably overestimated.
Abstract: Singular systems (or singular spectrum) analysis (SSA) was originally proposed for noise reduction in the analysis of experimental data and is now becoming widely used to identify intermittent or modulated oscillations in geophysical and climatic time series. Progress has been hindered by a lack of effective statistical tests to discriminate between potential oscillations and anything but the simplest form of noise, that is, “white” (independent, identically distributed) noise, in which power is independent of frequency. The authors show how the basic formalism of SSA provides a natural test for modulated oscillations against an arbitrary “colored noise” null hypothesis. This test, Monte Carlo SSA, is illustrated using synthetic data in three situations: (i) where there is prior knowledge of the power-spectral characteristics of the noise, a situation expected in some laboratory and engineering applications, or when the “noise” against which the data is being tested consists of the output of an independently specified model, such as a climate model; (ii) where a simple hypothetical noise model is tested, namely, that the data consists only of white or colored noise; and (iii) where a composite hypothetical noise model is tested, assuming some deterministic components have already been found in the data, such as a trend or annual cycle, and it needs to be established whether the remainder may be attributed to noise. The authors examine two historical temperature records and show that the strength of the evidence provided by SSA for interannual and interdecadal climate oscillations in such data has been considerably overestimated. In contrast, multiple inter- and subannual oscillatory components are identified in an extended Southern Oscillation index at a high significance level. The authors explore a number of variations on the Monte Carlo SSA algorithm and note that it is readily applicable to multivariate series, covering standard empirical orthogonal functions and multichannel SSA.

Journal ArticleDOI
TL;DR: In this paper, the effects of climate variability on snow water equivalent (SWE) over the western part of the conterminous United States are examined, focusing on measurements on/and 1 April, when snow accumulation is typically greatest.
Abstract: An important part of the water supply in the western United States is derived from runoff fed by mountain snowmelt Snow accumulation responds to both precipitation and temperature variations, and forms an interesting climatic index, since it integrates these influences over the entire late fall-spring period. Here, effects of cool season climate variability upon snow water equivalent (SWE) over the western part of the conterminous United States are examined. The focus is on measurements on/and 1 April, when snow accumulation is typically greatest. The primary data, from a network of mountainous snow courses, provides a good description of interannual fluctuations in snow accumulations, since many snow courses have records of five decades or more. For any given year, the spring SWE anomaly at a particular snow course is likely to be 25%–60% of its long-term average. Five separate regions of anomalous SWE variability are distinguished, using a rotated principal components analysis. Although effects...

Journal ArticleDOI
TL;DR: The binned probability ensemble (BPE) method as discussed by the authors is a method for predicting the probability distribution of a variable using an ensemble of numerical model integrations, where the ensemble forecasts are used to partition the real line into a number of bins, each of which has an equal probability of containing the forecast.
Abstract: The binned probability ensemble (BPE) technique is presented as a method for producing forecasts of the probability distribution of a variable using an ensemble of numerical model integrations. The ensemble forecasts are used to partition the real line into a number of bins, each of which has an equal probability of containing the “true” forecast. The method is tested for both a simple low-order dynamical system and a general circulation model (GCM) forced with observed sea surface temperatures (an ensemble of Atmospheric Model Intercomparison Project integrations). The BPE method can also be used to calculate the probability that probabilistic ensemble forecasts are consistent with the verifying observations. The method is not sensitive to the fact that the characteristics of the forecast probability distribution may change drastically for different initial condition (or boundary condition) probability distributions. For example, the method is capable of evaluating whether the variance of a set ...

Journal ArticleDOI
TL;DR: The role of the atmospheric circulation as a bridge between sea surface temperature (SST) anomalies in the tropical Pacific and those in the midlatitude northern oceans is assessed in this article.
Abstract: The role of the atmospheric circulation as a “bridge” between sea surface temperature (SST) anomalies in the tropical Pacific and those in the midlatitude northern oceans is assessed. The key processes associated with this atmospheric bridge are described using output from four independent simulations with a general circulation model subjected to month to month SST variations observed in the tropical Pacific during the 1946–1988 period and to climatological SST conditions elsewhere (the “TOGA” runs). In episodes with prominent SST anomalies in the tropical Pacific, extratropical perturbations in the simulated atmospheric temperature, humidity, and wind fields induce changes in the latent and sensible heat fluxes across the air-sea interface of the midlatitude oceans. These anomalous fluxes in turn lead to extratropical SST changes. The relevance of the atmospheric bridge mechanism is evaluated by driving a motionless, 50-m deep oceanic negative mixed layer model at individual grid points with the...

Journal ArticleDOI
TL;DR: In this paper, an efficient new prognostic cloud water parameterization designed for use in global climate models is described, which allows for life cycle effects in stratiform clouds and permits cloud optical properties to be determined interactively.
Abstract: An efficient new prognostic cloud water parameterization designed for use in global climate models is described. The scheme allows for life cycle effects in stratiform clouds and permits cloud optical properties to be determined interactively. The parameterization contains representations of all important microphysical processes, including autoconversion, accretion, Bergeron–Findeisen diffusional growth, and cloud/rain water evaporation. Small-scale dynamical processes, including detrainment of convective condensate, cloud-top entrainment instability, and stability-dependent cloud physical thickness variations, are also taken into account. Cloud optical thickness is calculated from the predicted liquid/ice water path and a variable droplet effective radius estimated by assuming constant droplet number concentration. Microphysical and radiative properties are assumed to be different for liquid and ice clouds, and for liquid clouds over land and ocean. The parameterization is validated in several s...

Journal ArticleDOI
TL;DR: In this article, a one-layer soil moisture model is proposed to improve the understanding of soil moisture and its effects on the atmosphere and apply the calculated soil moisture toward long-range temperature forecasts.
Abstract: A long time series of monthly soil moisture data during the period of 1931–1993 over the entire U.S. continent has been created with a one-layer soil moisture model. The model is based on the water budget in the soil and uses monthly temperature and monthly precipitation as input. The data are for 344 U.S. climate divisions during the period of 1931–1993. The main goals of this paper are 1) to improve our understanding of soil moisture and its effects on the atmosphere and 2) to apply the calculated soil moisture toward long-range temperature forecasts. In this study, the model parameters are estimated using observed precipitation, temperature, and runoff in Oklahoma (1960–1989) and applied to the entire United States. The comparison with the 8-yr (1984–1991) observed soil moisture in Illinois indicates that the model gives a reasonable simulation of soil moisture with both climatology and interannual variability. The analyses of the calculated soil moisture show that the climatological soil mois...

Journal ArticleDOI
TL;DR: In this article, the physical mechanisms responsible for the contemporaneous association of North Atlantic basin major hurricane activity with western Sahelian monsoon rainfall and an equatorial eastern Pacific sea surface temperature index of El Nino are examined, using correlations with 200-and 700-mb level wind data for the period 1968-92.
Abstract: Physical mechanisms responsible for the contemporaneous association, shown in earlier studies, of North Atlantic basin major hurricane (MH) activity with western Sahelian monsoon rainfall and an equatorial eastern Pacific sea surface temperature index of El Nino are examined, using correlations with 200- and 700-mb level wind data for the period 1968–92. The use of partial correlations isolates some of the relationships associated with the various parameters. The results support previous suggestions that the upper- and lower-level winds over the region in the basin between ∼10° and 20°N where most MHs begin developing are critical determinants of the MH activity in each hurricane season. In particular, interannual fluctuations in the winds that produce changes in the magnitude of vertical shear are one of the most important factors, with reduced shear being associated with increased activity and stronger shear with decreased activity. The results show that most of these critical wind fluctuations...

Journal ArticleDOI
TL;DR: In this article, the interannual variability in the strength of the tropical Hadley cells is investigated based on a 26-yr set of daily global upper-air wind data for the period January 1964-December 1989, the main focus is on the maximum in the streamfunction in the northern and southern Tropics.
Abstract: Based on a 26-yr set of daily global upper-air wind data for the period January 1964–December 1989, the interannual variability in the strength of the tropical Hadley cells is investigated. Although several measures of the intensity of the zonal-mean cells are discussed, the main focus is on the maximum in the streamfunction in the northern and southern Tropics. The streamfunction was computed from observed monthly mean latitude versus pressure cross sections of the zonal-mean meridional wind component. Significant seasonal variations are found in the strength, latitude, and height of the maximum streamfunction for both Hadley cells. Significant correlations are also observed between the Hadley cells and the El Nino-Southern Oscillation phenomenon. During the extreme seasons, only one “winter” Hadley cell dominates the Tropics, with the rising branch in the summer hemisphere and the sinking branch in the winter hemisphere. Superimposed on this “normal” one-cell winter Hadley circulation in the Tr...

Journal ArticleDOI
TL;DR: In this paper, the interannual variability of rainfall over the Indian subcontinent, the African Sahel, and the Nordeste region of Brazil have been evaluated in 32 models for the period 1979-88 as part of the Atmospheric Model Intercomparison Project (AMIP).
Abstract: The interannual variability of rainfall over the Indian subcontinent, the African Sahel, and the Nordeste region of Brazil have been evaluated in 32 models for the period 1979–88 as part of the Atmospheric Model Intercomparison Project (AMIP). The interannual variations of Nordeste rainfall are the most readily captured, owing to the intimate link with Pacific and Atlantic sea surface temperatures. The precipitation variations over India and the Sahel are less well simulated. Additionally, an Indian monsoon wind shear index was calculated for each model. Evaluation of the interannual variability of a wind shear index over the summer monsoon region indicates that the models exhibit greater fidelity in capturing the large-scale dynamic fluctuations than the regional-scale rainfall variations. A rainfall/SST teleconnection quality control was used to objectively stratify model performance. Skill scores improved for those models that qualitatively simulated the observed rainfall/El Nino- Southern Osc...

Journal ArticleDOI
TL;DR: In this article, the relationship between low-level jets and deep convection has been investigated and the potential for data from the Atmospheric Radiation Measurement (ARM) program to augment our understanding of LLJ is discussed.
Abstract: Low-level jets (LLJs) occur frequently in many parts of the world. These low-level wind speed maxima are important for both the horizontal and vertical fluxes of temperature and moisture and have been found to be associated with the development and evolution of deep convection. Since deep convective activity produces a significant amount of upper-level cloudiness and is responsible for a large fraction of the warm season rainfall in the United States, the relationship between LLJs and deep convection suggests that LLJs are important contributors to regional climate. Results from a number of past studies are reviewed, and the potential for data from the Atmospheric Radiation Measurement program to augment our understanding of low-level jets is discussed.

Journal ArticleDOI
TL;DR: In this article, a time series of near-surface meteorology from a buoy moored near the center of the COARE Intensive Flux Array (IFA) is described.
Abstract: A major goal of the Coupled Ocean-Atmosphere Response Experiment (COARE) was to achieve significantly more accurate and complete descriptions of the surface meteorology and air-sea fluxes in the western equatorial warm pool region. Time series of near-surface meteorology from a buoy moored near the center of the COARE Intensive Flux Array (IFA) are described here. The accuracies of the measurements and the derived fluxes are quantified; agreement between average net heat fluxes at the buoy and two nearby research ships is better than 10 W m−2 during three intercomparisons. Variability in the surface meteorology and fluxes associated with westerly wind bursts, periods of low winds, and short-lived, deep convective events characteristic of the region was large compared to the 4-month means. The ECMWF (European Centre for Medium-Range Weather Forecasts) analysis and prediction fields differed most from the buoy data during periods of short-lived, deep convective events, when several day averages of ...

Journal ArticleDOI
TL;DR: In this paper, a newly available, extensive compilation of upper-ocean temperature profiles was used to study the vertical structure of thermal anomalies between the surface and 400m depth in the North Pacific during 1970-1991.
Abstract: A newly available, extensive compilation of upper-ocean temperature profiles was used to study the vertical structure of thermal anomalies between the surface and 400-m depth in the North Pacific during 1970–1991. A prominent decade-long perturbation in climate occurred during this time period: surface waters cooled by ∼1°C in the central and western North Pacific and warmed by about the same amount along the west coast of North America from late 1976 to 1988. Comparison with data from COADS suggests that the relatively sparse sampling of the subsurface data is adequate for describing the climate anomaly. The vertical structure of seasonal thermal anomalies in the central North Pacific shows a series of cold pulses beginning in the fall of 1976 and continuing until late 1988 that appear to originate at the surface and descend with time into the main thermocline to at least 400-m depth. Individual cold events descend rapidly (∼100 m yr−1), superimposed upon a slower cooling (∼15 m yr−1). The inter...

Journal ArticleDOI
TL;DR: In this paper, an analysis of the spring-summer 1988 drought and 1993 floods over North America reveals a reversal in the sign of anomalies in several fields, implying a large-scale switch in the anomalous tropical heating and forcing of extratropical quasi-stationary waves in the atmosphere.
Abstract: An analysis of the spring–summer 1988 drought and 1993 floods over North America reveals a reversal in the sign of anomalies in several fields. Large sea surface temperature anomalies of opposite signs existed in the tropical Pacific with strong La Nina conditions in 1988 and a mature El Nino in 1993. The distribution of tropical convection in the convergence zones and associated latent heating of the atmosphere were correspondingly altered, implying a large-scale switch in the anomalous tropical heating and forcing of extratropical quasi-stationary waves in the atmosphere, influencing the subtropical jet stream over the North Pacific and across North America. In 1988 the jet stream and the closely related storm track of high-frequency disturbances in the upper troposphere were displaced into Canada well north of the normal location—the farthest north of any year from 1979 to 1993. In 1993 a broader jet stream and the storm track were displaced well south of normal to a more springlike location a...

Journal ArticleDOI
TL;DR: Arctic sea level pressure data from the period of the Arctic Ocean Buoy Program show a significant decrease in the annual mean as discussed by the authors, which indicates that the wind forcing of sea ice contains an enhanced cyclonic component relative to earlier decades.
Abstract: Arctic sea level pressure data from the period of the Arctic Ocean Buoy Program show a significant decrease in the annual mean. In every calendar month, the annual mean is lower in the second half of the 1979–1994 period than in the first. The changes of the annual means are larger in the central Arctic than anywhere else in the Northern Hemisphere. The decreases are largest and statistically significant in the autumn and winter. The annual anomalies became negative relative to the 16-yr mean in the 1980s and have been negative in every year since 1988. Correspondingly, the mean anticyclone in the Arctic pressure field has weakened and the vorticity of the gradient wind field over the central Arctic Ocean has become more positive than at any time in the past several decades. The pressure decrease, which has been compensated by pressure increases over the subpolar oceans, implies that the wind forcing of sea ice contains an enhanced cyclonic component relative to earlier decades.

Journal ArticleDOI
TL;DR: In this article, a strategy using statistically optimal fingerprints to detect anthropogenic climate change is outlined and applied to near-surface temperature trends, including observations, information about natural climate variability, and a "guess pattern" representing the expected time-space pattern of anthropogenic change.
Abstract: A strategy using statistically optimal fingerprints to detect anthropogenic climate change is outlined and applied to near-surface temperature trends. The components of this strategy include observations, information about natural climate variability, and a “guess pattern” representing the expected time–space pattern of anthropogenic climate change. The expected anthropogenic climate change is identified through projection of the observations onto an appropriate optimal fingerprint, yielding a scalar-detection variable. The statistically optimal fingerprint is obtained by weighting the components of the guess pattern (truncated to some small-dimensional space) toward low-noise directions. The null hypothesis that the observed climate change is part of natural climate variability is then tested. This strategy is applied to detecting a greenhouse-gas-induced climate change in the spatial pattern of near-surface temperature trends defined for time intervals of 15–30 years. The expected pattern of cl...

Journal ArticleDOI
TL;DR: In this article, a climatology of month to month changes in precipitation, using data from 4027 stations, illustrates how different climatic controls govern the annual cycle of precipitation response and explains the spatial distribution of the seasonal precipitation maximum.
Abstract: The western United States is characterized by complex seasonal precipitation regimes due to the hierarchy of climatic controls that operate at different spatial scales. A climatology of month to month changes in precipitation, using data from 4027 stations, illustrates how different climatic controls govern the annual cycle of precipitation response and explains the spatial distribution of the seasonal precipitation maximum. These results particularly indicate that smaller-scale climatic controls must be considered along with larger-scale ones in order to explain patterns of spatial climate heterogeneity over mountainous areas. The examination of seasonal precipitation maxima during years characterized by abnormally low winter Pacific-North American teleconnection (PNA) patterns and abnormally strong summer monsoons reveal few changes spatially as compared to normal. The lack of changes illustrate that spatial heterogeneity of precipitation seasonally is the rule rather than the exception for muc...

Journal ArticleDOI
TL;DR: In this article, microphysical processes responsible for the formation and dissipation of water and ice clouds have been incorporated into the Colorado State University General Circulation Model in order to yield a more physically based representation of the components of the atmospheric moisture budget.
Abstract: Microphysical processes responsible for the formation and dissipation of water and ice clouds have been incorporated into the Colorado State University General Circulation Model in order to 1) yield a more physically based representation of the components of the atmospheric moisture budget, 2) link the distribution and optical properties of the model-generated clouds to the predicted cloud water and ice amounts, and 3) produce more realistic simulations of cloudiness and the earth's radiation budget. The bulk cloud microphysics scheme encompasses five prognostic variables for the mass of water vapor, cloud water, cloud ice, rain, and snow. Graupel and hail are neglected. Cloud water and cloud ice are predicted to form through large-scale condensation and deposition processes and also through detrainment at the tops of cumulus towers. The production of rain and snow occur through autoconversion of cloud water and cloud ice. Rain drops falling through clouds can grow by collecting cloud water, and ...

Journal ArticleDOI
TL;DR: The relationship among clouds, surface radiation flux, and the sea surface temperature (SST) of the tropical western Pacific Ocean over the diurnal cycle is addressed in the context of the Atmospheric Radiation Measurement (ARM) Program scientific objectives.
Abstract: The relationship among clouds, surface radiation flux, and the sea surface temperature (SST) of the tropical western Pacific Ocean over the diurnal cycle is addressed in the context of the Atmospheric Radiation Measurement (ARM) Program scientific objectives for the tropical western Pacific Ocean. An understanding of the relationship between clouds and SST on a variety of time and space scales is needed to understand fully the cloud-radiation feedback in the tropical oceans and the maintenance of the warm pool. Here the diurnal cycle is emphasized. Data from the TOGA COARE Intensive Observation Period is examined and interpreted using an ocean mixed layer model that includes a parameterization of the “skin” temperature, explicit salinity, a surface beat budget that includes the sensible heat flux associated with rain, and the contribution of rain to the surface momentum flux. Using a mix of modeling and observations, three different case studies are examined in detail: clear and calm, clear and w...