Showing papers in "Journal of Climate in 1992"

An Intercomparison of Methods for Finding Coupled Patterns in Climate Data

Abstract: This paper introduces a conceptual framework for comparing methods that isolate important coupled modes of variability between time series of two fields. Four specific methods are compared: principal component analysis with the fields combined (CPCA), canonical correlation analysis (CCA) and a variant of CCA proposed by Barnett and Preisendorfer (BP), principal component analysis of one single field followed by correlation of its component amplitudes with the second field (SFPCA), and singular value decomposition of the covariance matrix between the two fields (SVD). SVD and CPCA are easier to implement than BP, and do not involve user-chosen parameters. All methods are applied to a simple but geophysically relevant model system and their ability to detect a coupled signal is compared as parameters such as the number of points in each field, the number of samples in the time domain, and the signal-to-noise ratio are varied. In datasets involving geophysical fields, the number of sampling times ma...

The Effect of Cloud Type on Earth's Energy Balance: Global Analysis

Abstract: The role of fractional area coverage by cloud types in the energy balance of the earth is investigated through joint use of International Satellite Cloud Climatology Project (ISCCP) C1 cloud data and Earth Radiation Budget Experiment (ERBE) broadband energy flux data for the one-year period March 1985 through February 1986. Multiple linear regression is used to relate the radiation budget data to the cloud data. Comparing cloud forcing estimates obtained from the ISCCP-ERBE regression with those derived from the ERBE scene identification shows generally good agreement except over snow, in tropical convective regions, and in regions that are either nearly cloudless or always overcast. It is suggested that a substantial fraction of the disagreement in longwave cloud forcing in tropical convective regions is associated with the fact that the ERBE scene identification does not take into account variations in upper-tropospheric water vapor. On a global average basis, low clouds make the largest contri...

Singular value decomposition of wintertime sea surface temperature and 500-mb height anomalies

Abstract: Single field principal component analysis (PCA), direct singular value decomposition (SVD), canonical correlation analysis (CCA), and combined principal component analysis (CPCA) of two fields are applied to a 39-winter dataset consisting of normalized seasonal mean sea surface temperature anomalies over the North Pacific and concurrent 500-mb height anomalies over the same region. The CCA solutions are obtained by linear transformations of the SVD solutions. Spatial patterns and various measures of the variances and covariances explained by the modes derived from the different types of expansions are compared, with emphasis on the relative merits of SVD versus CCA. Results for two different analysis domains (i.e., the Pacific sector versus a full hemispheric domain for the 500-mb height field) are also compared in order to assess the domain dependence of the two techniques. The SVD solution is also compared with the results of 28 Monte Carlo simulations in which the temporal order of the SST gri...

The Canadian Climate Centre Second-Generation General Circulation Model and Its Equilibrium Climate

Abstract: The Canadian Climate Centre second generation general circulation model (GCMII) is described. The description emphasizes aspects in which the new model differs from the 1984 model (GCMI) as described by Boer and collaborators. Important features of the new version include an interactive cloudiness parameterization, improved solar and terrestrial radiative beating calculations, a more sophisticated treatment of land surface processes, and a simple ocean mixed-layer model with a thermodynamic sea ice component. Results from a ten-year climate simulation made with the new model are presented and compared with observed climatology. The comparison is made for the December-February and June-August periods. The model reproduces the observed climatology in a generally successful manner.

Surface Temperature Patterns Associated with the Southern Oscillation

Abstract: The “typical” global and large-scale regional temperature patterns associated with the low (warm) and high (cold) phases of the Southern Oscillation (SO) are investigated. A total of 12 separate regions were found to have consistent temperature patterns associated with low phase of the SO, while 11 areas were found to have temperature patterns associated with the high phase. Of these areas, 9 have expected temperature patterns during both phases of the SO. In the tropics, temperature anomalies are of the same sign as the SO-related sea surface temperature (SST) anomaly in all land regions except for one area in the west Pacific. Three extratropical responses to the low phase of the SO are found over North America and one is found in Japan. High SO-temperature patterns were found in the extratropies for Japan, western Europe, and northwestern North America. The identified temperature responses are more consistent in tropical regions than in the extratropies. The SO can influence the estimation of ...

Latent and Sensible Heat Flux Anomalies over the Northern Oceans: The Connection to Monthly Atmospheric Circulation

Abstract: The influence of the atmospheric circulation on monthly anomalies of ocean surface latent and sensible heat fluxes is explored. The fluxes are estimated using bulk formulas applied to a set of about four decades of marine observations over 1946–1986. Monthly averaging over 5° “square” reduces errors contained in individual observations. The focus is on behavior of the flux anomalies over the relatively well-sampled North Atlantic and North Pacific ocean during winter, when the latent and sensible components are large and the incoming shortwave radiative flux is low. In the North Atlantic and North Pacific (north of about 15°N), flux anomalies are partially caused by local variations in the monthly mean wind direction. In these extratropical regions, largest positive anomalies occur during northerly to northwesterly winds in response to advection of humidity and temperature from north to south and also to favored directions experiencing strong wind speeds. In the tropics, there is little relations...

The Annual Cycle in Equatorial Convection and Sea Surface Temperature

Abstract: The coupled atmosphere-ocean system in the equatorial eastern Pacific and Atlantic exhibits a distinct annual cycle that is reflected in contrasting conditions at the times of the two equinoxes. The contrasts are so strong that they dominate the annual march of zonally averaged outgoing long wave radiation for the equatorial belt. The March equinox corresponds to the warm season when the equatorial cold tongues in the eastern Pacific and Atlantic area absent. With the onset of summer monsoon convection over Colombia, Central America, and West Africa in May-June, northward surface winds strengthen over the eastern Pacific and Atlantic, the equatorial cold tongues reappear, and the marine convection shifts from the equatorial belt to the intertropical convergence zones (ITCZs) along 8 deg N. On the basis of observational evidence concerning the timing and year-to-year regularity of the surface wind changes during the development of the cold tongues, it is argued that (1) the increase in the northward surface winds in response to the onset of the northern summer monsoon may be instrumental in reestablishing the cold tongues, and (2) positive feedbacks involving both the zonal and meridional wind components contribute to the remarkable robustness of the cold tongue-ITCZs complexes in both oceans.

The Effects of Orography on Midlatitude Northern Hemisphere Dry Climates

Abstract: The role of mountains in maintaining extensive midlatitude arid regions in the Northern Hemisphere was investigated using simulations from the GFDL Global Climate Model with and without orography. In the integration with mountains, dry climates were simulated over central Asia and the interior of North America, in good agreement with the observed climate. In contrast, moist climates were simulated in the same regions in the integration without mountains. During all season but summer, large amplitude stationary waves occur in response to the Tibetan Plateau and Rocky Mountains. The midlatitude dry regions are located upstream of the troughs of these waves, where general subsidence and relatively infrequent storm development occur and precipitation is thus inhibited. In summer, this mechanism contributes to the dryness of interior North America as a stationary wave trough remains east of the Rockies, but is not effective in Eurasia due to seasonal changes in the atmospheric circulation. The dryness...

The Atmospheric Circulation and Sea Surface Temperature in the North Atlantic Area in Winter: Their Interaction and Relevance for Iberian Precipitation

Abstract: The ocean surface-atmosphere relationships in the North Atlantic area in northern winter are empirically examined by canonical correlation analysis (CCA). This analysis is performed from two different points of view. First, the connection between atmospheric circulation anomalies, in terms of monthly mean sea level pressure (SLP) and monthly standard deviation of SLP (αSLP), and sea surface temperature (SST) anomalies of the Atlantic Ocean are directly examined. Second, the air-sea relationships are indirectly studied through their influence upon precipitation in an area likely to be influenced by the North Atlantic, the Iberian Peninsula. The canonical correlation analysis yields two pairs of patterns that describe the coherent variations of the combined SST-SLP fields; one pair of patterns for the SST-αSLP fields and one pair of patterns for the SLP-αSLP fields. All patterns are dominant in describing variance. A lag cross-correlation analysis of the time coefficients indicates that monthly mea...

Prediction of ENSO Episodes Using Canonical Correlation Analysis

Abstract: Canonical correlation analysis (CCA) is explored as a multivariate linear statistical methodology with which to forecast fluctuations of the El Nino/Southern Oscillation (ENSO) in real time. CCA is capable of identifying critical sequence of predictor patterns that tend to evolve into subsequent patterns that can be used to form a forecast. The CCA model is used to forecast the 3-month mean sea surface temperature (SST) in several regions of the tropical Pacific and Indian oceans for projection times of 0 to 4 seasons beyond the immediately forthcoming season. The predictor variables, representing the climate situation in the four consecutive 3-month periods ending at the time of the forecast, are 1) quasi-global seasonal mean sea level pressure (SLP) and 2) SST in the predictand regions themselves. Forecast skill is estimated using cross-validation, and persistence is used as the primary skill control measure. Results indicate that a large region in the eastern equatorial Pacific (120°−170°W lon...

Greenhouse Gas–induced Climate Change Simulated with the CCC Second-Generation General Circulation Model

Abstract: The Canadian Climate Centre second-generation atmospheric general circulation model coupled to a mixed-layer ocean incorporating thermodynamic sea ice is used to simulate the equilibrium climate response to a doubling of C02. Features of the simulation include the use of higher model resolution than previously for studies of this kind, specification of ocean heat transport for the open ocean and under sea ice, incorporation of information on vegetation and soil type in the treatment of land surface processes, and the inclusion of a parameterization of variable cloud optical properties. The results of the simulation indicate a global annual warming of 3.5°C with enhanced warming found over land and at higher latitudes. Precipitation and evaporation rates increase by about 4%, and cloud cover decreases by 2.2%. Soil moisture decreases over continental Northern Hemisphere land areas in summer. The frozen component of soil moisture decreases and the liquid component increases in association with the ...

A Zonally Averaged, Coupled Ocean-Atmosphere Model for Paleoclimate Studies

Abstract: A zonally averaged ocean model for the thermohaline circulation is coupled to a zonally averaged, one-layer energy balance model of the atmosphere to form a climate model for paleoclimate studies. The emphasis of the coupled model is on the ocean's thermohaline circulation in the Pacific, Atlantic, and Indian oceans. Each basin is individually resolved, and they are connected by the Southern Ocean through which mass, heat, and salt are exchanged. Under present-day conditions, the global conveyor belt is simulated: deep water is formed in the North Atlantic and the Southern Ocean, whereas both Pacific and Indian oceans show broad upwelling. Latitude-depth structures of modeled temperature and salinity fields, as well as depth-integrated meridional transports of heat and freshwater, compare well with estimates from observations when wind stress is included. Ekman cells are present in the upper ocean and contribute substantially to the meridional fluxes at low latitudes, bringing them to close agree...

Annual Cycle of Radiation Fluxes over the Arctic Ocean: Sensitivity to Cloud Optical Properties

Abstract: The relationship between cloud optical properties and the radiative fluxes over the Arctic Ocean is explored by conducting a series of modeling experiments. The annual cycle of arctic cloud optical properties that are required to reproduce both the outgoing radiative fluxes at the top of the atmosphere as determined from satellite observations and the available determinations of surface radiative fluxes are derived. Existing data on cloud fraction and cloud microphysical properties are utilized. Four types of cloud are considered: low stratus clouds, midlevel clouds, cirrus clouds, and wintertime ice crystal precipitation. Internally consistent annual cycles of surface temperature, surface albedo, cloud fraction and cloud optical properties, components of surface and top of atmosphere radiative fluxes, and cloud radiative forcing are presented. The modeled total cloud optical depth (weighted by cloud fraction) ranges from a low value in winter of 2 to a high summertime value of 8. Infrared emmiss...

The Strong Association between Western Sahelian Monsoon Rainfall and Intense Atlantic Hurricanes

Abstract: Seasonal variability of Atlantic basin tropical cyclones is examined with respect to the monsoon rainfall over West Africa. Variations of intense hurricanes are of the most interest, as they are responsible for over three-quarters of United States tropical cyclone spawned destruction, though they account for only one-fifth of all landfalling cyclones. Intense hurricanes have also shown a strong downward trend during the last few decades. It is these storms that show the largest concurrent association with Africa's western Sahelian June-September rainfall for the years 1949–90. Though the Sahel is currently experiencing a multidecadal drought, the relationship between Atlantic tropical cyclones and western Sahelian rainfall is not dependent on the similar downward trends in both datasets. A detrended analysis confirms that a strong association still exists, though reduced somewhat in variance explained. Additionally, independent data from the years 1899 to 1948 substantiate the existence of the tr...

A Global Monthly Sea Surface Temperature Climatology

Abstract: The paper presents a new global 2 deg x 2 deg monthly sea surface temperature (SST) climatology, referred here to as the Shea-Trenberth-Reynolds (STR) climatology, which was derived by modifying a 1950-1979-based SST climatology from the Climate Analysis Center (CAC), by using data from the Comprehensive Ocean-Atmosphere Data Set to improve the SST estimates in the regions of the Kuroshio and the Gulf Stream. A comparison of the STR climatology with the Alexander and Mobley SST climatology showed that the STR climatology is warmer in the Northern Hemisphere, and colder poleward of 45 deg S.

Low-Level Temperature Inversions of the Eurasian Arctic and Comparisons with Soviet Drifting Station Data

Abstract: Seasonal and regional variations in characteristics of the Arctic low-level temperature inversion are examined using up to 12 years of twice-daily rawinsonde data from 31 inland and coastal sites of the Eurasian Arctic and a total of nearly six station years of data from three Soviet drifting stations near the North Pole. The frequency of inversions, the median inversion depth, and the temperature difference across the inversion layer increase from the Norwegian Sea eastward toward the Laptev and East Siberian seas. This effect is most pronounced in winter and autumn, and reflects proximity to oceanic influences and synoptic activity, possibly enhanced by a gradient in cloud cover. East of Novaya Zemlya during winter, inversions are found in over 95% of all soundings and tend to be surface based. For all locations, however, inversions tend to he most intense during winter due to the large deficit in surface net radiation. The strongest inversions are found over eastern Siberia, and reflect the ef...

Further case studies of tropical Atlantic surface atmospheric and oceanic patterns associated with sub-Saharan drought

Abstract: Sub-Saharan West Africa (10°–20°N) receives rainfall from westward-propagating disturbance lines that have their base within and receive most of their moisture from the low-level, wedge-shaped, southwest monsoonal flow off the tropical Atlantic. This paper builds on earlier research to further identify the tropical Atlantic surface atmospheric and oceanic patterns that accompany drought in sub-Saharan West Africa. Patterns for the four driest years since 1940 (1972, 1977, 1983, 1984) are compared with counterparts for the wettest of the last 20 years (1975) and 60-year (1911–70) average fields. The key results for the rainy season (July-September) of three of the four severe sub-Saharan drought years (1972, 1977, 1984) duplicate those obtained earlier. They include (i) a distinctive basinwide sea surface temperature (SST) anomaly pattern (positive departure to the south of ∼10°N; negative departures between 10°–25°N); (ii) a concomitant southward displacement (relative to the 1911–70 mean) of the...

Modeling Interannual Variations of Summer Monsoons

Abstract: Results from a set of 90-day integrations, made with a T42 version of the ECMWF model and forced with a variety of specified sea surface temperature (SST) datasets, are discussed. Most of the integrations started from data for 1 June 1987 and 1 June 1988. During the summer of 1987, both the Indian and African monsoons were weak, in contrast with the summer of 1988 when both monsoons were much stronger. With observed SSTs, the model is able to simulate the interannual variations in the global-scale velocity potential and stream-function fields on seasonal time scales. On a regional basis, rainfall over the Sahel and, to a lesser extent, India showed the correct sense of interannual variation, though in absolute terms the model appears to have an overall dry bias in these areas. Additional integrations were made to study the impact of the observed SST anomalies in individual oceans. Much of the interannual variation in both Indian and African rainfall can be accounted for by the remote effect of th...

Characteristics of Low-Frequency Sea Surface Temperature Fluctuations in the Tropical Atlantic

Abstract: Sea surface temperature anomalies in the tropical Atlantic Ocean are reexamined to investigate an apparent low-frequency oscillation that has been described as a fluctuating dipole structure with poles north and south of the equator and a node near the ITCZ. Using principal components rotated by the varimax method and simple correlations of area-averaged temperatures, we show that during the 1964–88 interval SST anomalies north and south of the ITCZ are not significantly correlated. Therefore, the low-frequency variation, with an apparent decadal period observed in the SST gradient across the ITCZ during 1964–88, does not arise from temporally coherent and out-of-phase fluctuations in each hemisphere and cannot be characterized as a dipole.

The Sensitivity of the ECMWF Model to the Parameterization of Evaporation from the Tropical Oceans

Abstract: Stimulated by the results of a simple SST anomaly experiment with the ECMWF forecast model, a study was carried out to examine the model parameterization of evaporation from the tropica] oceans. In earlier versions of the model, these fluxes were parameterized with neutral transfer coefficients in accordance with the Charnock relation with equal coefficients for momentum, heat, and moisture. Stability correction was applied using Monin-Obukhov theory. This parameterization resulted in an extremely weak coupling between atmosphere and ocean at wind speeds below 5 m s−1. The transfer coefficients for heat and moisture have now been modified for low wind speeds to bring them in accordance with the empirical scaling law for free convedion. It is shown that these revisions to the transfer coefficients at very low wind speeds (<5 m s1) have a dramatic positive impact on almost all aspects of the model's simulation of the tropics. These include much improved seasonal rainfall distributions (with the vir...

Tree-Ring Density Reconstructions of Summer Temperature Patterns across Western North America since 1600

Abstract: Summer half-year (April-September) mean temperatures are reconstructed across western North America between 1600 and 1982. The reconstructions, ultimately in the form of gridpoint anomaly time series, are produced using a principal-components regression technique to relate variability in a network of up to 53 high-elevation maximum latewood-density chronologies to a number of important temperature principal-component amplitude series. The reconstructions are of good quality over the area between 35° and 55°N but are subject to large uncertainty north of 55°N, particularly prior to 1750. Four regional time series, the average of between two and six gridpoint series—British Columbia and the Pacific Northwest, California, eastern Rockies and northern High Plains, and the Southwest deserts—plus one more-extensive western United States series are presented and described. Examples of individual-year and decadal-mcan anomaly maps are illustrated, and the results of preliminary spectral analyses of the r...

Variability in Large-Scale Water Balance with Land Surface-Atmosphere Interaction

Abstract: Persistent and prolonged periods of dry or moist conditions are often evident in the interannual variability of continental-type climates This variability appears as fluctuations around several distinct and preferred moisture states. These fluctuations and transitions between the preferred states are commonly attributed to large-scale changes in atmospheric circulation patterns possibly caused by oceanic influence. This paper argues that a major contributing factor to the persistent dry or moist behavior could be due to feedback and nonlinear interaction between the components of the hydrologic cycle in both the land and the atmosphere. A model that couples the water balance of continental landmasses and the overlying atmosphere is presented. The large-scale variabilities in atmospheric circulation are introduced by way of simple randomness in key forcing parameters. The result is a multiplicative-noise stochastic differential equation for the water balance dynamics of continental-type climates t...

Issues in Establishing Causes of the 1988 Drought over North America

Abstract: The causes and physical mechanisms involved in the 1988 North American drought are investigated. The issue of when the drought circulation anomalies developed and their relation to changes in tropical Pacific SSTs is examined. The evolution of the Pacific SSTs and tropical convection, as revealed by outgoing LW radiation, is shown to be consistent with the development of the conditions favorable for initiating the drought circulation pattern in April through June of 1988. On the equator at 110 deg W, SST anomalies exceeded -2.75 C only in April, May, and June, and were largest (-4.1 C) in May 1988. Diagnostic calculations of atmospheric diabatic heating confirm that atmospheric heating anomalies existed in the tropical Pacific in association with the major SST anomalies during this time. It is argued that feedback-caused soil moisture anomalies were secondary sources for the drought circulation but could not have been the primary instigator.

Empirical analysis of dry spells for agricultural applications in West Africa

Abstract: Recurring droughts and decreased agricultural productivity during the last two decades in West Africa point to the need for a clearer understanding of the length of dry spells, their frequencies and their probabilities. The simplest calculations of dry spells for general applications involve computation of the probabilities of maximum and conditional dry spells exceeding a user-specified threshold value from a given calendar date. For more precise applications in agriculture, it is important to consider the different periods after sowing a crop, since sowing dates in the semiarid West African regions vary from year to year. Using the specific definition of onset of rains in each year as the sowing date, the length of dry cells was calculated from the historical rainfall data. Probability distribution of time to the next wet day and the percentage frequencies of dry spells were computed for successive days after sowing (DAS) a crop. Dry-spell analysis showed a pronounced drop in the drought risk f...

Climatic Fluctuations and the Timing of West Coast Streamflow

Abstract: Since about 1950 there has been a trend in the California Sierra Nevada toward a decreasing portion of the total annual streamflow occurring during April through July, while the streamflow during autumn and winter has increase. This trend not only has important ramifications with regard to water management, it also brings up the question of whether this represents a shift toward earlier release of the snowpack resulting from greenhouse warming. Therefore, the observed record has been examined in terms of relative influences of temperature and precipitation anomalies on the timing of streamflow in this region. To carry out this study, the fraction of annual streamflow (called the fractional streamflow) occurring in November-January (NDJ), February-April (FMA), and May-July (MJJ) at low, medium, and high elevation basins in California and 0regon was examined. Linear regression models were used to relate precipitation and temperature to the fractional streamflow at the three elevations for each seas...

Observed Tropospheric Biennial Variability and Its Relationship to the Southern Oscillation

Abstract: Tropospheric biennial variability in several components of the Southern Oscillation (SO) is defined and described through analysis of observational data from the Comprehensive Ocean-Atmosphere Data Set (COADS), as well as through investigation of several SO index time series The analysis suggests that the temporal behavior of the SO can be described in terms of three components: 1) a pervasive biennial pulse, which appears to be strong in both the Indian Ocean and the west Pacific surface zonal winds as well as in several SO indices, 2) the annual cycle, which tends to set the phase of biennial variability for the major SO excursions, and 3) a low-frequency, or residual, variability, which may be associated with temporal scales between large SO episodes This study also supports recent papers in suggesting that complete models of the SO must include the Indian Ocean basin

The Sensitivity of Regional Transpiration to Land-Surface Characteristics: Significance of Feedback

Abstract: Several authors have determined the sensitivity of transpiration to different environmental parameters using the Penman-Monteith equation. In their studies the interaction between transpiration and, for example, the humidity of the air is ignored: the feedback with the planetary boundary layer (PBL) is not accounted for. Furthermore, surface-layer (SL) feedback (e.g., stability effects in the surface layer) is often neglected. In our study, both PBL feedback and SL feedback are accounted for by coupling the big-leaf model to a detailed model for the PBL. This study provides an analysis of the sensitivity of transpiration to net radiation calculated after an albedo change, aerodynamic resistance calculated after a change in the aerodynamic roughness, and surface resistance. It is shown that PBL feedback affects the sensitivity of transpiration to the tested variables significantly. The sensitivity of transpiration to surface resistance and to aerodynamic resistance, or aerodynamic roughness, is de...

Interannual Variability of Wintertime Snow Cover across the Northern Hemisphere

Abstract: Digitized maps of Northern Hemisphere snow cover derived from visible satellite imagery are examined to assess the interannual variability of snow cover in winter months for years 1972–90. The secular trend of winter snow cover over the landmasses of Eurasia and North America during this period is extremely small in December and January. A decreasing trend of somewhat larger magnitude is observed in Eurasian snow cover in February. Fluctuations of detrended interannual snow-cover anomalies averaged over the Eurasian and North American continents are positively correlated. By subdividing the continents into longitudinal sectors it is determined that this intercontinental relationship is due to high correlations between European and North American sectors. The relationship of snow-cover fluctuations to large-scale circulation anomalies is described using lime series of teleconnection pattern indices derived from monthly mean geopotential height fields. A pattern of height anomalies resembling the N...

A comparative analysis of two land surface heterogeneity representations

Abstract: Two contrasting representations of land surface variability used in general circulation models (GCMs) are compared through an analysis of their corresponding surface energy balance equations. In one representation (the 'mixture' approach), different vegetation types are assumed to be homogeneously mixed over a grid square, so that the GCM atmosphere sees near-surface conditions pertaining to the mixture only. In the second representation (the 'mosaic' approach), different vegetation types are viewed as separate 'tiles' of a grid-square 'mosaic', and each tile interacts with the atmosphere independently. The mosaic approach is computationally simpler and in many ways more flexible than the mixture approach. Analytical solutions to the linearized energy balance equations and numerical solutions to the nonlinear equations both demonstrate that the mixture strategy, when applied to two coexisting vegetation types that differ only in canopy transpiration resistance, promotes both total turbulent flux and latent heat flux relative to the mosaic strategy. The effective differences between the strategies, however, are small over a wide range of conditions. In particular, the strategies are effectively equivalent when the transpiration resistances of the different vegetation types are of the same order of magnitude.

Midlatitude Atmosphere–Ocean Interaction during El Niño. Part I: The North Pacific Ocean

Abstract: Atmosphere-ocean experiments are experiments are used to investigate the formation of sea surface temperature (SST) anomalies in the North Pacific Ocean during fall and winter of the El Nino year. Experiments in which the NCAR Community Climate Model (CCM) surface fields am used to force a mixed-layer ocean model in the North Pacific (no air-sea feedback) are compared to simulations in which the CCM and North Pacific Ocean model are coupled. Anomalies in the atmosphere and the North Pacific Ocean during El Nino are obtained from the difference between simulations with and without prescribed warm SST anomalies in the tropical Pacific. In both the forced and coupled experiments, the anomaly pattern resembles a composite of the actual SST anomaly field during El Nino: warm SSTs develop along the cost of North America and cold SSTs form in the central Pacific. In the coupled simulations, air-sea interaction results in a 25% to 50% reduction in the magnitude of the SST and mixed-layer depth anomalies ...