The seasonal cycle of the global zonally averaged energy balance

Summary The annual and seasonal cycle of the global zonally averaged storage and transport of moist static energy (MSE), the surface eddy flux of MSE, and the radiation budget at the top of the atmosphere (TOA) and surface are investigated in this paper. We use the GFDL (Geophysical Fluid Dynamics Laboratory) zonal mean data to compute the storage rate, divergence, and poleward flux of MSE. Surface eddy fluxes are determined based on an empirical formula developed from available climatological data. Radiative fluxes at the TOA and surface are computed from a radiation model. A number of significant features are illustrated by the present analysis in regard to the global annual and seasonal energy balance of the earth-atmosphere system. The storage/release rate of MSE is greater in spring and autumn than in summer and winter. The rate of poleward transport of MSE has a maximum at ~40°N and ~35°S with a value of ~3 × 10¹⁵ W. In terms of the radiation budget, the persistent ITCZ minimum and subtropical maxima of the IR flux distribution are reproduced well in the radiation parameterization program. The incoming solar flux maximum shifts from ~20°N in spring to ~40°N in summer due to the poleward increase in the fraction of daytime. Finally, an examination of the global surface energy balance reveals that the surface net fluxes derived from parameterizations for eddy and radiative fluxes agree well with values derived from observations. This agreement appears to imply that on the global mean, the physical parameterizations used in the present study are reliable in modeling the seasonal surface flux components.

---

Zusammenfassung Der jährliche und jahreszeitliche Gang der globalen Zonenmittel der Speicherung und des Transports von latenter Energie (MSE), des Oberflächen-Eddy-Flusses der MSE und des Einstrahlungsbudgets an der Atmosphärengrenze (TOA) als auch auf der Erdoberfläche werden untersucht.Wir verwenden die GFDL Zonenmitteldaten, um die Ladung, Divergenz und den polgerichteten Fluß der MSE zu errechnen. Die Oberflächen-Eddy-Flüsse werden aufgrund einer empirischen Formel bestimmt, die mittels verfügbarer klimatologischer Daten erstellt wurde. Strahlungsflüsse auf der Oberfläche und der Atmosphärengrenze werden mittels eines Einstrahlungsmodells errechnet. Eine Reihe signifikanter Erscheinungen werden in der vorliegenden Analyse dargestellt mit Hinblick auf das globale jährliche und jahreszeitliche Energiegleichgewicht des Erde-Atmosphäre-Systems. Die Ladungs- und Entladungsrate des MSE ist im Frühjahr und Herbst größer als im Sommer und Winter. Die Spitzen des polgerichteten Transports der MSE liegen bei 40° N und 35° S mit einem Wert von ca. 3 × 10¹⁵ W. In bezug auf das Einstrahlungsbudget werden die persistenten ITKZ-Minima und die subtropischen Maxima der IR-Flußverteilung gut von dem Einstrahlungsparameterisierungsprogramm dargestellt. Die Sonneneinstrahlungsflußspitzen verschieben sich von 20° N im Frühjahr nach 40° im Sommer aufgrund der gegen den Pol hin zunehmenden Tageslänge. Zuletzt zeigen die Untersuchungen des globalen Oberflächenenergiegleichgewichts auf, daß die Oberflächennettoflüsse, abgeleitet von der Parameterisierung für Eddy- und Einstrahlungsflüsse, mit den beobachteten Werten gut übereinstimmen. Diese Übereinstimmung impliziert offensichtlich, daß im globalen Durchschnitt die physikalische Parametrisierung, die in dieser Studie angewendet wurde, verläßliche Modelle der jahreszeitlichen Oberflächenflußkomponenten liefern kann.

---

---

With 8 Figures     

Index of direction change of zonally averaged wind and change of season

In this paper, a Wind Direction Change Index (WI), which can describe four-dimensional spatiotemporal changes of the atmospheric circulation objectively and quantitatively, is defined to study its evolution and seasonal variation. The first four modes can be obtained by EOF expansion of the zonally averaged WI. The first mode reveals the basic spatial distribution of the annually averaged WI. The second mode reflects the quasi-harmonic parts of the WI deviations. Tropical, subtropical and extratropical monsoon areas can be clearly reflected by this mode. The third mode reflects the non-harmonic parts of the WI deviations. It shows the so-called February reverse in stratospheric atmosphere as well as the asymmetric seasonal changes from spring to fall and from fall to spring due to both the land-sea distribution contrast between the Northern and Southern Hemispheres and the nonlinear effect of atmospheric and ocean fluids. The fourth mode reveals the northward advancing of the global reversed wind fields from spring to summer and their southward withdrawal from summer to autumn.     

Methane,carbon monoxide and methylchloroform in the southern hemisphere

New observational data on CH₄, CO and CH₃CCl₃ in the southern hemisphere are reported. The data are analysed for long term trends and seasonal cycles. CH₃CCl₃ data are used to scale the OH fields incorporated in a two dimensional model, which in turn, is used to constrain the magnitude of a global CH₄ source function. The possible causes of observed seasonality of CH₃CCl₃, CH₄ and CO are identified, and several other aspects of observed CH₄ variability are discussed.Possible future research directions are also given.     

Comparison of the main characteristics of the daily zonally averaged surface air temperature as represented by reanalysis and seven CMIP3 models

This paper analyses the ability exhibited by seven coupled global climate models of the Climate Model Inter-comparison Project 3 used in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change to simulate current zonally averaged surface air temperature (ZASAT) meridional profiles. The expansion in second order of ZASAT profiles by means of Legendre polynomials was compared with the same expansion carried out over the ZASAT profiles provided by the ERA40 and National Centers for Environmental Prediction reanalysis from 1961 to 1998. According to the theoretical support provided by the one-dimensional energy balance models (1D-EBMs), the Legendre coefficients corresponding to the ZASAT profile can be qualitatively interpreted as the independent modes that represent the meridional energy flux from the equator to the poles. We find that three models, MIROC3.2-MR, MIROC3.2-HR and MPI-ECHAM5 may be considered as the models that best reproduce the meridional structure of current ZASAT, although the differences between the models are not really large. Consequently, the results shown in this paper support the accuracy of the models in representing the poleward meridional heat fluxes and global thermal inertia under the qualitative interpretation provided by the 1D-EBM approach.     

Mean annual poleward energy transports by the oceans in the southern hemisphere

A survey is made of the published estimates of the components of the poleward flux of energy by the atmosphere in the Southern Hemisphere in order to determine the total atmospheric transport. Together with recent measurements by satellite of the Earth's radiation budget this allows a new estimate of the required poleward energy transport by the oceans in the Southern Hemisphere for mean annual conditions. Results show that the ocean and atmosphere each contribute similar amounts for 0–30°S and that the ocean probably also transports about one third of the total at 60°S. The latter is in contrast to similar latitudes in the Northern Hemisphere where the ocean transport is negligible, but consistent with the different distribution of land and sea in the two hemispheres.     

Moisture and heat budgets of the south American monsoon system: climatological aspects

The climatology of the moisture and heat budget equation terms for subareas within the South American Monsoon System (SAMS) region is investigated for the 1958–2014 period considering the distinct phases of the Pacific Decadal Oscillation (PDO). These budget equations are applied to the data from the National Centers for Environmental Prediction (NCEP) Reanalysis project. Sources or sinks of moisture and heat are equation residues, referred to as residue and diabatic terms, respectively. Analyses are done for the Central Amazon Basin (CAM) and Western-Central Brazil (WCB) for three distinct periods, 1958–1976, 1977–1995, and 1996–2014, that correspond to the cold, warm, and undefined PDO phases. The differences among the PDO phases for each term are discussed. The CAM region acts dominantly as a moisture sink and heat source in all months during the three phases. On the other hand, in the WCB region, the monsoon characteristics are better defined, with a moisture sink (source) and a heat source (sink) during the wet (dry) season. The main result of the present analysis is the persistence of SAMS intensification signs in both CAM and WCB areas up to the last analyzed period (1996–2014), which is consistent with intense flooding in the Amazon Basin in 2008/2009, 2012, and 2014.     

Large-scale oscillations of the atmospheric circulation in the southern hemisphere and their influence on climate change in some regions of the globe in the 20th century

The Antarctic Oscillation and its connections with other modes of large-scale circulation and climate parameter variations are studied from the reanalysis data. The estimates of tendencies of the current Antarctic climate changes are presented. It is considered whether the reanalysis data are suitable in studying the Antarctic climate and its changes. The results of the intercomparison of the reanalysis data with station observation and with statistics calculated from these data are discussed.     

High-frequency patterns of the atmospheric circulation over the southern hemisphere and South America

Summary Daily 500-hPa geopotential height and 250-hPa meridional wind reanalyzed data obtained from the National Centers for Environmental Prediction are used to document austral winter (May to September) and summer (November to March) high-frequency variability in the Southern Hemisphere (SH) midlatitudes for the 1990–1994 period. Empirical orthogonal function (EOF) technique is used to determine the high-frequency patterns for these variables in selected areas. The high-frequency anomalous 500-hPa geopotential height patterns for two areas in the SH midlatitudes (the zonally global domain and the western hemisphere) and the high-frequency anomalous 250-hPa meridional wind patterns in the western hemisphere between 15° N and 70° S are discussed. The high-frequency winter and summer patterns for both variables feature a wavetrain structure in the SH midlatitudes which is related to synoptic-scale systems, such as cyclones and anticyclones associated with frontal zones. The dominant high-frequency patterns in the SH midlatitudes manifest in the eastern hemisphere while the secondary ones appear in the southeastern Pacific. Analysis of the western hemisphere data reveal that the wavetrain in the South American sector extends northeastward over the continent, thus affecting the regional weather conditions. An important result presented here concerns the preference of the intense synoptic systems in the eastern hemisphere and in the southeastern Pacific to occur in a sequential instead of an intermittent fashion. This result might have a potential for being used in weather monitoring.     

Signature of a southern hemisphere extratropical influence on the summer monsoon over India

The weakening relationship of El Nino with Indian summer monsoon reported in recent years is a major issue to be addressed. The altered relationships of Indian monsoon with various parameters excite to search for other dominant modes of variability that can influence the precipitation pattern. Since the Indian summer monsoon circulation originates in the oceanic region of the southern hemisphere, the present study investigates the association of southern extratropical influence on Indian summer monsoon using rainfall and reanalysis parameters. The effect of Southern Annular Mode (SAM) index during the month of June associated with the onset phase of Indian summer monsoon and that during July–August linked with the active phase of the monsoon were analysed separately for a period from 1951 to 2008. The extra-tropical influence over the monsoon is illustrated by using rainfall, specific humidity, vertical velocity, circulation and moisture transport. The June high SAM index enhances the lower level wind flow during the onset phase of monsoon over Indian sub-continent. The area of significant positive correlation between precipitation and SAM in June also shows enhancement in both ascending motion and specific humidity during the strong phase of June SAM. On the other hand, the June high SAM index adversely affects July–August monsoon over Indian subcontinent. The lower level wind flow weakens due to the high SAM. Enhancement of divergence and reduction in moisture transport results in the Indian monsoon region due to the activity of this high southern annular mode. The effect is more pronounced over the southwest region where the precipitation spell has high activity during the period. Significant correlation exists between SAM and ISMR, even after removing the effect of El Nino. It indicates that the signals of Indian summer monsoon characteristics can be envisaged to a certain extend using the June SAM index.     

A diagnostic study of the southern hemisphere summer circulation of the CCC general circulation model

Abstract

The medium‐scale wave regime, consisting largely of zonal wavenumbers 5–7, frequently dominates the summer Southern Hemisphere tropospheric circulation. We perform a diagnostic study of this circulation as simulated by the Canadian Climate Centre (CCC) general circulation model (GCM). The analysis of Hövmöller diagrams, space‐time and zonal wavenumber spectra shows that the CCC GCM is able to simulate the observed medium‐scale wave regime.

The zonally averaged meridional eddy heat and momentum transports and the associated baroclinic and barotropic energy conversions are also examined. The distributions of the transports on the vertical plane agree well with the observations. After comparison with the observed December‐January‐February 1979 distributions, some quantitative differences remain: the heat transport is too weak aloft and too large near the surface, whereas the momentum transport tends to be too weak. The baroclinic and barotropic conversions show a maximum in the medium‐scale waves. The time evolution of the Richardson number of the mean flow suggests that the medium‐scale wave is due to a baroclinic instability.     

On the vertically averaged balance equation of atmospheric trace constituents

Summary The vertically averaged balance equation of atmospheric trace constituents that customarily serves as a basis for one- and two-layer (box) models of the atmospheric boundary layer and the whole troposphere is derived and discussed. It is shown that this kind of balance equation is accompanied by several prominent short-comings so that the capability of such models to predict real situations of photochemical smog formation and depletion is strongly limited. Three of these short-comings are theoretically elucidated, namely (1) the vertically averaged source and sink terms owing to chemical reactions, (2) the parameterisation of the dry deposition and exhalation fluxes at the earths surface that serve as lower boundary conditions, and (3) the parameterisation of the upper boundary conditions. Even though the consumption of computing time is much smaller than those of sophisticated Eulerian air pollution models like ADOM, DRAIS, EURAD, RADM, and TADAP, we have to conclude from our theoretical results that one- and two-layer (box) models should not be considered as a true alternative to such air pollution models.We also suggest that the influence of these short-comings on the predicted results has to be estimated and evaluated in a reliable manner before vertically averaged balance equations of atmospheric trace constituents are introduced into general circulation models to investigate the influence of air pollution on climate change on the basis of long-term simulations.     

On the dispersion of particles in the atmosphere

The method of moments is used to predict the spatial and temporal dispersion of a cloud of particles released in the atmosphere. The moment equations involve an eddy diffusivity, and a turbulence parameterization is developed to obtain the tensor eddy diffusivity which takes into account the anisotropy of the flow. The parabolic equations for the moments of the distribution are solved by a finite element method. The differences between the data requirements for Lagrangian statistical models and those for eddy diffusivity models are discussed in relation to the comparison of model predictions with observations.     

Characterizing the zonally asymmetric component of the SH circulation

Much research concerning the Southern Hemisphere (SH) zonally asymmetric circulation has focused on the Pacific-South American mode (PSA) or the major zonal waves. However, these large-scale decompositions may mask important local variability. In this paper the month-to-month variability explained by the zonal waves 1 and 3 is examined, and an alternative representation of the SH circulation is presented based on two quasi-stationary anticyclones in the sub-Antarctic western hemisphere. These anticyclones are related to the zonal waves, but features of their variability are masked by the zonal wave decomposition; in particular, the anticyclones’ strengths are not positively covariant. They are also compared with the leading Principal Components of the SH atmosphere. We show that they capture variance independent of the Southern Annular Mode. Additionally, they explain a generally greater fraction of the variability than the PSA, and in a manner that also includes information regarding spatial variability. These results have implications for analysis of the atmospheric-forcing of western Antarctic climate.     

Northward flux of zonal velocity due to quasi-stationary and nonstationary waves in the atmosphere during northern hemisphere winter

The zonal wind velocity flux induced by wave motions in the central month of winter (January) is studied from the NCEP/NCAR reanalysis data and the general circulation model (GCM) of the Institute of Numerical Mathematics of the Russian Academy of Sciences (INM RAS). It is shown that the model describes stationary wave processes with a sufficient accuracy and captures their synoptic period.