Showing papers in "Journal of Climate in 1995"
TL;DR: In this paper, it is argued from SST observations for the period 1950-90 that the tropical Indo-Pacific ocean-atmosphere system may be described as a stable linear dynamical system driven by spatially coherent Gaussian white noise.
Abstract: It is argued from SST observations for the period 1950–90 that the tropical Indo-Pacific ocean-atmosphere system may be described as a stable linear dynamical system driven by spatially coherent Gaussian white noise. Evidence is presented that the predictable component of SST anomaly growth is associated with the constructive interference of several damped normal modes after an optimal initial structure is set up by the white noise forcing. In particular, El Nino–Southern Oscillation (ENSO) growth is associated with an interplay of at least three damped normal modes, with periods longer than two years and decay times of 4 to 8 months, rather than the manifestation of a single unstable mode whose growth is arrested by nonlinearities. Interestingly, the relevant modes are not the three least damped modes of the system. Rather, mode selection, and the establishment of the optimal initial structure from which growth occurs, are controlled by the stochastic forcing. Experiments conducted with an empir...
808 citations
TL;DR: In this paper, the sea ice-albedo feedback mechanism over the Arctic Ocean multi-year sea ice is investigated by conducting a series of experiments using several one-dimensional models of the coupled sea ice atmosphere system.
Abstract: The sea ice-albedo feedback mechanism over the Arctic Ocean multiyear sea ice is investigated by conducting a series of experiments using several one-dimensional models of the coupled sea ice-atmosphere system. In its simplest form, ice-albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature, further decreasing the areal cover of snow and ice. It is shown that the sea ice-albedo feedback can operate even in multiyear pack ice, without the disappearance of this ice, associated with internal processes occurring within the multiyear ice pack (e.g., duration of the snow cover, ice thickness, ice distribution, lead fraction, and melt pond characteristics). The strength of the ice-albedo feedback mechanism is compared for several different thermodynamic sea ice models: a new model that includes ice thickness distribution, the Ebert and Curry model, the Maykut and Untersteiner model, and the Semtner level-3 an...
654 citations
TL;DR: In this article, a new classification system for seasonal snow covers is proposed, which has six classes (tundra, taiga, alpine, maritime, prairie, and ephemeral) defined by a unique ensemble of textural and stratigraphic characteristics.
Abstract: A new classification system for seasonal snow covers is proposed. It has six classes (tundra, taiga, alpine, maritime, prairie, and ephemeral, each class defined by a unique ensemble of textural and stratigraphic characteristics including the sequence of snow layers, their thickness, density, and the crystal morphology and grain characteristics within each layer. The classes can also be derived using a binary system of three climate variables: wind, precipitation, and air temperature. Using this classification system, the Northern Hemisphere distribution of the snow cover classes is mapped on a 0.5° lat × 0.5° long grid. These maps are compared to maps prepared from snow cover data collected in the former Soviet Union and Alaska. For these areas where both climatologically based and texturally based snow cover maps are available, there is 62% and 90% agreement, respectively. Five of the six snow classes are found in Alaska. From 1989 through 1992, hourly measurements, consisting of 40 thermal and...
628 citations
TL;DR: The characteristics of the onset of the Pacific basin-wide warming have experienced notable changes since the late 1970s as mentioned in this paper, caused by a concurrent change in the background state on which El Nino evolves.
Abstract: The characteristics of the onset of the Pacific basin-wide warming have experienced notable changes since the late 1970s. The changes are caused by a concurrent change in the background state on which El Nino evolves. For the most significant warm episodes before the late 1970s (1957, 1965, and 1972), the atmospheric anomalies in the onset phase (November to December of the year preceding the El Nino) were characterized by a giant anomalous cyclone over east Australia whose eastward movement brought anomalous westerlies into the western equatorial Pacific, causing development of the basin-wide warming. Meanwhile, the trades in the southeastern Pacific (20°S–0°, 125°–95°W) relaxed back to their weakest stage, resulting in a South American coastal warming, which led the central Pacific warming by about three seasons. Conversely, in the warm episodes after the late 1970s (1982, 1986–87, and 1991), the onset phase was characterized by an anomalous cyclone over the Philippine Sea whose intensification...
519 citations
TL;DR: In this paper, a new version of the ECMWF land surface parameterization scheme is described, which has four prognostic layers in the soil for temperature and soil moisture, with a free drainage and a zero heat flux condition at the bottom as a boundary condition.
Abstract: A new version of the ECMWF land surface parameterization scheme is described. It has four prognostic layers in the soil for temperature and soil moisture, with a free drainage and a zero heat flux condition at the bottom as a boundary condition. The scheme has been extensively tested in stand-alone mode with the help of long observational time series from three different experiments with different climatological regimes: the First ISLSCP (International Satellite Land Surface Climatology Project) Field Experiment in the United States, Cabauw in the Netherlands, and the Amazonian Rainforest Meteorological Experiment in Brazil. The emphasis is on seasonal timescales because it was felt that the main deficiencies in the old ECMWF land surface scheme were related to its capability of storing precipitation in spring and making it available for evaporation later in the year. It is argued that the stand-alone testing is particularly important, because it allows one to isolate problems in the land surface...
517 citations
TL;DR: In this article, it is shown that the revised Student's t-test is often conservative when the equivalent sample size is known, but becomes liberal when the true equivalent sample sizes is large (greater than approximately 30).
Abstract: The comparison of means derived from samples of noisy data is a standard pan of climatology. When the data are not serially correlated the appropriate statistical tool for this task is usually the conventional Student's t-test. However, frequently data are serially correlated in climatological applications with the result that the t test in its standard form is not applicable. The usual solution to this problem is to scale the t statistic by a factor that depends upon the equivalent sample size ne. It is shown, by means of simulations, that the revised t tea is often conservative (the actual significance level is smaller than the specified significance level) when the equivalent sample size is known. However, in most practical cases the equivalent sample size is not known. Then the test becomes liberal (the actual significance level is greater than the specified significance level). This systematic error becomes small when the true equivalent sample size is large (greater than approximately 30). ...
447 citations
TL;DR: The satellite-gauge model (SGM) as discussed by the authors combines microwave satellite data with infrared satellite data, rain gauge analyses, and numerical weather prediction models into improved estimates of global precipitation.
Abstract: The 'satellite-gauge model' (SGM) technique is described for combining precipitation estimates from microwave satellite data, infrared satellite data, rain gauge analyses, and numerical weather prediction models into improved estimates of global precipitation. Throughout, monthly estimates on a 2.5 degrees x 2.5 degrees lat-long grid are employed. First, a multisatellite product is developed using a combination of low-orbit microwave and geosynchronous-orbit infrared data in the latitude range 40 degrees N - 40 degrees S (the adjusted geosynchronous precipitation index) and low-orbit microwave data alone at higher latitudes. Then the rain gauge analysis is brougth in, weighting each field by its inverse relative error variance to produce a nearly global, observationally based precipitation estimate. To produce a complete global estimate, the numerical model results are used to fill data voids in the combined satellite-gauge estimate. Our sequential approach to combining estimates allows a user to select the multisatellite estimate, the satellite-gauge estimate, or the full SGM estimate (observationally based estimates plus the model information). The primary limitation in the method is imperfections in the estimation of relative error for the individual fields. The SGM results for one year of data (July 1987 to June 1988) show important differences from the individual estimates, including model estimates as well as climatological estimates. In general, the SGM results are drier in the subtropics than the model and climatological results, reflecting the relatively dry microwave estimates that dominate the SGM in oceanic regions.
437 citations
TL;DR: In this paper, the time-mean response over the tropical Pacific region to a quadrupling of CO2 is investigated using a global coupled ocean-atmosphere general circulation model.
Abstract: The time-mean response over the tropical Pacific region to a quadrupling Of CO2 is investigated using a global coupled ocean-atmosphere general circulation model. Tropical Pacific sea surface temperatures (SSTs) rise by about 4°–5°C. The zonal SST gradient along the equator decreases by about 20%, although it takes about one century (with C02 increasing at 1% per year compounded) for this change to become clearly evident in the model. Over the central equatorial Pacific, the decreased SST gradient is accompanied by similar decreases in the easterly wind stress and westward ocean surface currents and by a local maximum in precipitation increase. Over the entire rising branch region of the Walker circulation, precipitation is enhanced by 15%, but the time-mean upward motion decreases slightly in intensity. The failure of the zonal overturning atmospheric circulation to intensify with a quadrupling of CO2 is surprising in light of the increased time-mean condensation heating over the “warm pool” reg...
435 citations
TL;DR: In this article, a series of regression analyses indicate that runoff timing responds equally to the observed decadal-scale trends in winter temperature and interannual temperature variations of the same magnitude.
Abstract: Since the late 1940s, snowmelt and runoff have come increasingly early in the water year in many basins in northern and central California. This subtle trend is most pronounced in moderate-altitude basins, which are sensitive to changes in mean winter temperatures. Such basins have broad areas in which winter temperatures are near enough to freezing that small increases result initially in the formation of less snow and eventually in early snowmelt. In moderate-altitude basins of California, a declining fraction of the annual runoff has come in April–June. This decline has been compensated by increased fractions of runoff at other, mostly earlier, times in the water year. Weather stations in central California, including the central Sierra Nevada, have shown trends toward warmer winters since the 1940s. A series of regression analyses indicate that runoff timing responds equally to the observed decadal-scale trends in winter temperature and interannual temperature variations of the same magnitude...
425 citations
TL;DR: In response to the development of a new higher-resolution sea surface temperature (SST) analysis at the National Meteorological Center (NMC), a new monthly 1° global SST climatology was constructed from two intermediate climatologies as discussed by the authors.
Abstract: In response to the development of a new higher-resolution sea surface temperature (SST) analysis at the National Meteorological Center (NMC), a new monthly 1° global sea surface temperature climatology was constructed from two intermediate climatologies: the 2° SST climatology presently used at NMC and a 1° SST climatology derived from the new analysis. The 2° SST climatology used a 30-yr 1950–1979 base period between roughly 40°S and 60°N based on in situ (ship and buoy) SST data supplemented by four years (1982–1985) of satellite SST retrievals. The 1° SST climatology was based on monthly analyses using in situ SST data, satellite SST retrievals, and sea-ice coverage data over a 12-yr period (1982–1993). The final climatology was combined from these two products so that a 1° resolution was maintained and the base period was adjusted to the 1950–1979 period wherever possible (approximately between 40°S and 60°N). Compared to the 2° climatology, the 1° climatology resolves equatorial upwelling an...
410 citations
TL;DR: In this article, the authors examined the impact of major volcanic eruptions on surface temperature in the past 140 years and found that after 2 years following great volcanic outbreaks, the surface cools significantly by 0.1°-0.2°C in the global mean, in each hemisphere, and in the summer in the latitude bands 0°-30°S and 0° -30°N and 0.3°C
Abstract: Climate records of the past 140 years are examined for the impact of major volcanic eruptions on surface temperature. After the low-frequency variations and El Nino/Southern Oscillation signal are removed, it is shown that for 2 years following great volcanic eruptions, the surface cools significantly by 0.1°–0.2°C in the global mean, in each hemisphere, and in the summer in the latitude bands 0°–30°S and 0°–30°N and by 0.3°C in the summer in the latitude band 30°–30°60°N. By contrast, in the first winter after major tropical eruptions and in the second winter after major high-latitude eruptions, North America and Eurasia warm by several degrees, while northern Africa and southwestern Asia cool by more than 0.5°C. Because several large eruptions occurred at the same time as ENSO events, the warming produced by the ENSO masked the volcanic cooling during the first year after the eruption. The timescale of the ENSO response is only 1 year while the volcanic response timescale is 2 years, so the coo...
TL;DR: In this paper, an intercomparison of various cluster techniques was carried out on a well-studied dataset (7-day precipitation data from 1949 to 1987 in central and eastern North America).
Abstract: Cluster analysis (CA) has been applied to geophysical research for over two decades although its popularity has increased dramatically over the past few years. To date, systematic methodological reviews have not appeared in geophysical literature. In this paper, after a review of a large number of applications on cluster analysis, an intercomparison of various cluster techniques was carried out on a well-studied dataset (7-day precipitation data from 1949 to 1987 in central and eastern North America). The cluster methods tested were single linkage, complete linkage, average linkage between groups, average linkage within a new group, Ward's method, k means, the nucleated agglomerative method, and the rotated principal component analysis. Three different dissimilarity measures (Euclidean distance, inverse correlation, and theta angle) and three initial partition methods were also tested on the hierarchical and nonhierarchical methods, respectively. Twenty-two of the 23 cluster algorithms yielded na...
TL;DR: In this paper, the authors successfully model and simulate the observed evidence that anomalously high winter/spring Eurasian snow cover is linked to weak rainfall in the following summer Indian monsoon.
Abstract: The authors successfully model and simulate the observed evidence that anomalously high winter/spring Eurasian snow cover is linked to weak rainfall in the following summer Indian monsoon. It is shown that excessive snow cover in February reduces June to September precipitation over India. The excessive snow cover is associated with a weak monsoon characterized by higher sea level pressure over India, a weaker Somali jet, weaker lower tropospheric westerlies, and weaker upper tropospheric easterlies. The weak monsoon is also associated with weaker secondary circulations. The remote response to excessive Eurasian snow cover is to reduce the strength of trade winds in the eastern equatorial Pacific Ocean. Energy used in melting excessive snow reduces the surface temperature over a broad region centered around the Tibetan Plateau. Reduced surface sensible heat flux reduces the midtropospheric temperature over the Tibetan Plateau. The result is to reduce the midtropospheric meridional temperature gra...
TL;DR: For the period 1987 to 1993, quantities central to the global moisture budget from the global analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF), the U.S. National Meteorological Center (NMC), and NASA/Goddard have been computed and compared as discussed by the authors.
Abstract: For the period 1987 to 1993, quantities central to the global moisture budget from the global analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF), the U.S. National Meteorological Center (NMC), and NASA/Goddard have been computed and compared. The precipitable water is computed and compared with satellite data from the Special Sensor Microwave Imager (SSM/I). Fluxes of moisture and their divergence have been used to estimate the vertically integrated moisture budget and thus evaporation minus precipitation (E − P) as residuals. Results of several test computations show that small biases exist in precipitable water as vertical resolution and methods of computing vertical integrals are changed, but the impact is small on the moisture budget. In the Tropics and subtropics the moisture budget is dominated by the divergence field rather than the moisture amounts, and consequently initialization of the analyses has an impact on the perceived moisture budget. The diurnal cycle is ...
TL;DR: In this paper, the amplitude of the seasonal cycle is affected by interannual variations in the depth of the thermocline and in threedimensional depth of a tropical region in the central and eastern tropical Pacific.
Abstract: Wavelet transforms, which can unfold signals in both time and frequency domains, are used to analyze the Comprehensive Ocean and Atmospheric Data Sets for the period 1870–1988. The focus is on secular changes in the interannual variability and the annual cycle of selected equatorial regions. The amplitude of El Nino/Southern Oscillation (ENSO) is found to be large from 1885 to 1915, to be small during the period 1915–1950, and to increase rapidly after about 1960. Surprisingly, the decadal variations in the amplitude of ENSO are not matched by similar decadal variations in the amplitude of the annual cycle. On short timescales of 2–5 years, ENSO strongly influences the annual cycle in certain parts of the central and eastern tropical Pacific where the thermocline is shallow. The annual cycle is weak in warm El Nino years and is strong in cold La Nina years. This result suggests that the amplitude of the seasonal cycle is affected by interannual variations in the depth of the thermocline and in th...
TL;DR: In this article, an EMF analysis of winter sea surface temperature (SST) anomalies over the Pacific domain (60°N-20°S) reveals an El Nino-Southern Oscillation (ENSO) mode that is linked to the eastern North Pacific, and a North Pacific mode linearly independent of ENSO.
Abstract: Empirical orthogonal function analysis of winter sea surface temperature (SST) anomalies over the Pacific domain (60°N–20°S) reveals an El Nino-Southern Oscillation (ENSO) mode that is linked to the eastern North Pacific, and a North Pacific mode that is linearly independent of ENSO. The North Pacific mode exhibits maximum amplitude and variance explained along ∼40°N, west of ∼170°W. SSTs in this region have decreased by ∼1.5°C from 1950 to 1987. The cooling in winter has been associated with a strengthening of the overlying westerly winds.
TL;DR: In this paper, the associated anomaly patterns of the stratospheric geopotential height field and the tropospheric and temperature height fields of the Northern Hemisphere are determined applying the canonical correlation analysis.
Abstract: The associated anomaly patterns of the stratospheric geopotential height field and the tropospheric geopetential and temperature height fields of the Northern Hemisphere are determined applying the canonical correlation analysis. With this linear multivariate technique the coupled modes of variability of lime series of two fields are isolated in the space of empirical orthogonal functions. The one dataset is the 50-hPa geopotential height field; the other set consists of different height fields of the tropospheric pressure levels (200, 500, 700, and 850 hPa) and the temperature of the 850-hPa pressure level. For the winter months (December, January, February) two natural coupled modes, a barotropic and a baroclinic one, of linear relationship between stratospheric and tropospheric circulation are found. The baroclinic mode describes a connection between the strength of the stratospheric cyclonic winter vortex and the tropospheric circulation over the North Atlantic. The corresponding temperature ...
TL;DR: A two-month, springtime simulation with the Goddard Earth Observing System (GEOS-1) atmospheric general circulation model (AGCM) has produced a Great Plains LLJ with a vertical and temporal structure, directionality, and climatological distribution that compare favorably with observations as mentioned in this paper.
Abstract: The Great Plains region of the United States is characterized by some of the most frequent and regular occurrences of a nocturnal low-level jet (LLJ). While the LLJ is generally confined to the lowest Kilometer of the atmosphere, it may cover a substantial region of the Great Plains, and typically reaches maximum amplitudes of more than 20 m s−1. A two-month, springtime simulation with the Goddard Earth Observing System (GEOS-1) atmospheric general circulation model (AGCM) has produced a Great Plains LLJ with a vertical and temporal structure, directionality, and climatological distribution that compare favorably with observations. The diurnal cycle of the low-level flow is dramatic and coherent over a subcontinental area that includes much of the western United States and northern Mexico. This cycle can be interpreted as the nightly intrusion of the anticyclonic, subtropical gyre (associated with the Bermuda high) into the North American continent as surface friction decreases. The AGCM also sim...
TL;DR: The isopycnal transport parameterization of Gent and Mc Williams has been implemented in the GFDL ocean general circulation model, replacing the physically unjustifiable horizontal mixing of tracers.
Abstract: The isopycnal transport parameterization of Gent and Mc Williams has been implemented in the GFDL ocean general circulation model, replacing the physically unjustifiable horizontal mixing of tracers. The effects of this parameterization are investigated in a global domain. A comparison of its results with those of the conventional horizontal diffusion shows substantial and significant improvements in several climatically important aspects of the ocean circulation. These improvements include a sharper main thermocline, cooler abyssal ocean, elimination of the Deacon cell as a tracer transport agent, zonally integrated meridional heat transport and surface heat fluxes in better agreement with observations, and better confinement of the locations where deep convection occurs. The sensitivity of the model to the magnitude of the horizontal and isopycnal diffusion coefficients is also studied, showing that the domain averages of potential temperature and salinity, the mass transport of the Antarctic C...
TL;DR: In this paper, the authors describe the initialization of an experiment to study the time-dependent response of a high-resolution global coupled ocean-atmosphere general circulation model to a gradual increase in carbon dioxide.
Abstract: This paper describes the initialization of an experiment to study the time-dependent response of a high-resolution global coupled ocean-atmosphere general circulation model to a gradual increase in carbon dioxide. The stability of the control integration with respect to climate drift is assessed, and aspects of the model climatology relevant to the simulation of climate change are discussed. The observed variation of oceanic temperature with latitude and depth is basically well simulated, although, in common with other ocean models, the main thermocline is too diffuse. Nevertheless, it is found that large heat and water flux adjustments must be added to the surface layer of the ocean in order to prevent the occurrence of unacceptable climate drift. The ocean model appears to achieve insufficient meridional heat transport, and this is supported by the pattern of the heat flux adjustment term, although errors in the simulated atmosphere-ocean heat flux also contribute to the latter. The application...
TL;DR: The GENESIS version 1.02 as discussed by the authors is a modified version of the NCAR CCM1 and includes semi-Lagrangian transport of water vapor, subgrid plume convection, PBL mixing, and a more complex cloud scheme.
Abstract: The present-day climatology of a global climate model (GENESIS Version 1.02) is described. The model includes a land-surface transfer component (LSX) that accounts for the physical effects of vegetation. The atmospheric general circulation model is derived from the NCAR CCM1 and modified to include semi-Lagrangian transport of water vapor, subgrid plume convection, PBL mixing, a more complex cloud scheme, and a diurnal cycle. The surface models consist of LSX; multilayer models of soil, snow, and sea ice; sea ice dynamics; and a slab mixed layer ocean. Brief descriptions of the current model components are included in an appendix. GENESIS is an ongoing project to develop an earth system model prototype for global change research. The Version 1.02 climate model has already proved useful in paleoclimate studies. Results of present-day simulations are described using an atmospheric spectral resolution of RIS (∼4.5° lat×7.5° long) and a surface-model resolution of 2°×2°. In general the quality of the...
TL;DR: In this article, a high-resolution coupled ocean-atmosphere model has been used to simulate the transient response of climate to a gradual increase in atmospheric carbon dioxide concentrations, and the mechanisms leading to this reduction are discussed.
Abstract: A high-resolution (2.75° lat × ° 3.75° long) coupled ocean-atmosphere model has been used to simulate the transient response of climate to a gradual increase in atmospheric carbon dioxide concentrations. Although the radiative forcing increases linearly, there is a delay of about 30 yr before the ocean warms appreciably. This “cold start” is, at least partly, an artifact of the experimental design. At the time of doubling (after 70 yr), the patterns of change are similar to those found in comparable studies of the equilibrium response, except in the high latitudes of the Southern Ocean and the North Atlantic, where the warming is considerably reduced. The mechanisms leading to this reduction are discussed. After two to three decades, the pattern of warming is well established. The warming over land is substantially larger than that over the sea, with a consequent lowering of surface pressure over the northern continents in summer. The patterns of changes in precipitation and soil moisture take lo...
TL;DR: In this paper, a threshold level of illuminance of moonlight or twilight on the cloud top was determined, above which the clouds are apparently detected adequately, and this threshold corresponds to light from a full moon at an elevation angle of 6 degrees, light from partial moon at higher elevation, or twilight from the sun less than 9 degrees from the horizon.
Abstract: Ten years of nighttime weather observations from the Northern Hemisphere in December were classified according to the illuminance of moonlight or twilight on the cloud tops, and a threshold level of illuminance was determined, above which the clouds are apparently detected adequately. This threshold corresponds to light from a full moon at an elevation angle of 6 deg, light from a partial moon at higher elevation, or twilight from the sun less than 9 deg bvelow the horizon. It permits the use of about 38% of the observations made with the sun below the horizon. The computed diurnal cycles of total cloud cover are altered considerably when this moonlight criterion is imposed. Maximum cloud cover over much of the ocean is now found to be at night or in the morning, whereas computations obtained without benefit of the moonlight criterion, as in our published atlases, showed the time of maximum to be noon or early afternoon in many regions. The diurnal cycles of total cloud cover we obtain are compared with those of the International Satellite Cloud Climatology Project (ISCCP) for a few regions; they are generally in better agreement if the moonlight criterion is imposed on the surface observations. Using the moonlight criterion, we have analyzed 10 years (1982-91) of surface weather observations over land and ocean, worldwide, for total cloud cover and for the frequency of occurrence of clear sky, fog, and precipitation. The global average cloud cover (average of day and night) is about 2% higher if the moonlight criterion is imposed than if all observations are used. The difference is greater in winter than in summer, because of the fewer hours of darkness in summer. The amplitude of the annual cycle of total cloud cover over the Arctic Ocean and at the South Pole is diminished by a few percent when the moonlight criterion is imposed. The average cloud cover for 1982-91 is found to be 55% for Northern Hemisphere land, 53% for Southern Hemisphere land, 66% for Northern Hemisphere ocean, and 70% for Southern Hemisphere ocean, giving a global average of 64%. The global average for daytime is 64.6%; for nighttime 63.3%.
TL;DR: A climatology of Antarctic sea ice extent based on 20 years of data (1973-1992) is presented in this article, including measures of interannual variability and extrema.
Abstract: A climatology of Antarctic sea ice extent based on 20 years of data (1973–1992) is presented, including measures of interannual variability and extrema. In the first half of the year the greatest variability is found in the Western Hemisphere, particularly in the Weddell and Ross Sea regions, while in the second semester the variability displays a considerable degree of zonal symmetry. We have used this dataset to explore the possible links between Antarctic sea ice extent and the Southern Oscillation Index (SOI). To do this we have calculated their correlation for all pairings of calendar months, as well as with the SOI taken from the year before and subsequent to that of the time of the sea ice data. Most of the correlations assume their largest magnitude when the SOI leads the anomalies in the sea ice, but these differ considerably between the three ocean basins. The extent of Indian Ocean sea ice in the months April through July is positively correlated with the SOI during most of the previou...
TL;DR: In this paper, the authors use data from six of these stations from different climatic regimes, along with ancillary meteorological and actinometric data, to demonstrate a method to validate soil moisture simulations with biosphere and bucket models.
Abstract: Soil moisture observations in sites with natural vegetation were made for several decades in the former Soviet Union at hundreds of stations In this paper, the authors use data from six of these stations from different climatic regimes, along with ancillary meteorological and actinometric data, to demonstrate a method to validate soil moisture simulations with biosphere and bucket models Some early and current general circulation models (GCMs) use bucket models for soil hydrology calculations More recently, the Simple Biosphere Model (SiB) was developed to incorporate the effects of vegetation on fluxes of moisture, momentum, and energy at the earth's surface into soil hydrology models Until now, the bucket and SiB have been verified by comparison with actual soil moisture data only on a limited basis In this study, a Simplified SiB (SSiB) soil hydrology model and a 15-cm bucket model are forced by observed meteorological and actinometric data every 3 h for 6-yr simulations at the six stations The model calculations of soil moisture are compared to observations of soil moisture, literally 'ground truth,' snow cover, surface albedo, and net radiation, and with each other For three of the stations, the SSiB and 15-cm bucket models produce good simulations of seasonal cycles and interannual variations of soil moisture For the other three stations, there are large errors in the simulations by both models Inconsistencies in specification of field capacity may be partly responsible There is no evidence that the SSiB simulations are superior in simulating soil moisture variations In fact, the models are quite similar since SSiB implicitly has a bucket embedded in it One of the main differences between the models is in the treatment of runoff due to melting snow in the spring -- SSiB incorrectly puts all the snowmelt into runoff While producing similar soil moisture simulations, the models produce very different surface latent and sensible heat fluxes, which would have large effects on GCM simulations
TL;DR: The long-term record of observations from Ocean Weather Station (OWS) November (N), which operated at 30°N, 140°W from 1949 to 1974, is analyzed to document the relationships among boundary layer cloud structure, sea surface temperatures (SSTs), and atmospheric circulation as discussed by the authors.
Abstract: The long-term record of observations from Ocean Weather Station (OWS) November (N), which operated at 30°N, 140°W from 1949 to 1974, is analyzed to document the relationships among boundary layer cloud structure, sea surface temperatures (SSTs), and atmospheric circulation. During the oceanic summer season, June through September, OWS N lay in the steady trade wind flow of the northeast Pacific. Boundary layer air parcels, which pass through the location of N, are typically in transition from the solid stratus or stratocumulus of the North Pacific to trade cumulus that is characteristic of the subtropics. Cloud observations indicate that low-cloud amount is high, averaging 70%, despite the absence of a well-mixed boundary layer. Low-cloud type code 8, cumulus and stratocumulus with bases at different levels, is the most frequently reported cloud type at all hours of the day. These observations suggest that along the stratus to trade cumulus transition, high cloud amount can exist long after the b...
TL;DR: In this article, a land surface model that includes a subgrid parameterization for inland water (lake, swamp, marsh) was coupled to a modified version of the NCAR CCM2.
Abstract: A land surface model that includes a subgrid parameterization for inland water (lake, swamp, marsh) was coupled to a modified version of the NCAR CCM2 The coupled model was run for 5 yr with and without inland water subgrid points to determine the importance of inland water for global climate simulation In July, the inclusion of these water bodies resulted in a spatially consistent signal in which high inland water regions were 2°–3°C cooler, had increased latent heat flux (10–45 W m−2), and decreased sensible heat flux (5–30 W m−2) compared to the simulation without these water bodies These changes were statistically significant in the lake region of northwest Canada, the Great Lakes region of North America, the swamp and marsh region of the Siberian lowlands, and the lake region of East Africa, but were not significantly different in the swamp and marsh region of Finland and northwest Russia The effect on Northern Hemisphere January air temperature was difficult to interpret due to large in
TL;DR: The surface radiative fluxes of the ECHAM3 General Circulation Model (GCM) with T2 1, T42, and T 106 resolutions have been validated using observations from the Global Energy Balance Archive (GEBA, World Climate Program-Water Project A7) as mentioned in this paper.
Abstract: The surface radiative fluxes of the ECHAM3 General Circulation Model (GCM) with T2 1, T42, and T 106 resolutions have been validated using observations from the Global Energy Balance Archive (GEBA, World Climate Program-Water Project A7). GEBA contains the most comprehensive dataset now available for worldwide instrumentally measured surface energy fluxes. The GCM incoming shortwave radiation at the surface has been compared with more than 700 long-term monitoring stations. The ECHAM3 models show a clear tendency to overestimate the global annual-mean incoming shortwave radiation at the surface due to an underestimation of atmospheric absorption. The model-calculated global-mean surface shortwave absorption around 165 W m−2 is estimated to be too high by 10–15 W m−2. A similar or higher overestimate is present in several other CYCMS. Deficiencies in the clear-sky absorption of the ECHAM3 radiation scheme are proposed as a contributor to the flux discrepancies. A stand-alone validation of the radi...
TL;DR: In this article, the authors used a simple model consisting only of first and second-mode baroclinic Kelvin waves to represent the observed amplitude and found that the second mode was essential to properly represent the amplitude.
Abstract: Equatorial Kelvin and Rossby waves associated with the 1991–93 El Nino warm event were detected in temperature observations made by the Tropical Atmosphere-Ocean (TAO) buoy array. Intraseasonal Kelvin waves were a prominent part of equatorial thermocline depth variability and were well represented by a simple model consisting only of first- and second-mode baroclinic Kelvin waves. The second mode was essential to properly represent the observed amplitude. Thermocline depth variability at 5°N and 5°S was dominated by annual and interannual Rossby waves, which were found to have been largely wind forced in midbasin, with little if any signal associated with eastern boundary reflection. An evaluation of the Wyrtki buildup hypothesis and the delayed oscillator hypothesis in connection with the 1991–93 events showed that a long lag (about two years) occurred between the arrival of the downwelling signal in the west and the subsequent initiation of El Nino., this was considerably longer than suggested ...
TL;DR: In this article, the regional precipitation climatology of South America during austral summer is studied by means of an R30 general circulation model (GCM) and results from perpetual January experiments, which differ only in their distributions of topography and sea surface temperature (SST), are presented.
Abstract: The regional precipitation climatology of South America during austral summer is studied by means of an R30 general circulation model (GCM). Results from perpetual January experiments, which differ only in their distributions of topography and sea surface temperature (SST), are presented. The precipitation field of the most realistic experiment compares well with the observed January precipitation climatology of South America. reproducing, in particular, five regions of maximum precipitation. To understand how structure in the surface conditions is mapped onto the precipitation field. the results of the three GCM experiments are compared. Continentality, through the generation of a thermal low, is responsible for much of the structure in the modeled precipitation field of South America. Topography introduces orographic precipitation maxima in the Central and Southern Andes and modifies precipitation rates elsewhere. Longitudinal structure in SSTs, which is also largely an expression of continenta...