large-scale circulations convecting atmospheres’ J. David Neelin - PDF document

large-scale circulations convecting atmospheres’ J. David Neelin and Christopher Bretherton (July B, A. RANDALL, and MICHAEL tangential winds versus time for four simulations. Cases surface fluxes increasing amounts available potential energy in the initial conditions, saturated boundary layer. AE is the control run with surface fluxes stopped 134 hours. Case the control. cases are initially unstable the linear upper panel fact that does not the early flaw of in stating implicitly assumed that the depression forms over tropical oceans where there near-saturated air in the surface boundary Charney and Eliassen (1964; hereafter acknowledge the important role of the warm ocean, though in attempting under certain circumstances, larger-scale disturbances their linear analysis failed account explicitly the energetic role surface fluxes. Although it was not cited clear on the issue surface fluxes. In a experiments (results which are plotted in and reproduced in demonstrated that irrespective either the predictions the linear analysis the amount in the initial conditions, the continual generation of instability through surface fluxes tropical-storm-like vortices amplify and maintain themselves near hurricane strength. Because goes on conclude that . . the supply of heat moisture directly warm ocean crucial requirement of a tropical cyclone’. introduced the phrase ‘conditional instability the second kind*’. Does mean that Ooyama (1964; hereafter which mention the phrase or the acronym, are irrelevant of the ideas behind the acronym? Because the similarities between being explored, with similar technique) are often cited explores and CE64 and first addressed using linear analysis. Because many people, certainly Ooyama, identified term CISK ideas raised in (as opposed particular models explore those ideas), can be interpreted as an investigation of point explicitly when states his . . the conceptual content that has grown with advances in modeling work’. Because definitions are ultimately matters opinion, discussions the merits the theory run the risk of degenerating semantical debates rather real scientific issues (cf. Consequently, in addressing the merits in general, and the validity of ENB’s criticisms in perspectives, which we group three schools as discussed which is explicitly contained in the models cooperative interaction between convection and large-scale circulations (CIBCLSC). this school constrain CISK to be any linear Others argue theory that is predominantly driven an advective-convective which surface fluxes are at most second-order effect. Others might in terms models which employ a particular parametrization (i.e. which is moisture convergence), irrespective the energy source disturbance. Still others One can trace the this idea back as 1959, section NOTES AND CORRESPONDENCE 1773 any CIBCLSC that has a specific combination above features. Because fundamental flaws a variety CISK can in a sufficiently narrow manner. For instance, linear models are describe finite-amplitude have historically fundamental processes such as many of the simple models are (e.g. Stark 1976; Pedersen and Rasmussen 1985; Emanuel 1993). its conceptual content as applied as first demonstrated school has come to fundamentally nonlinear process surface fluxes are often-overlooked result support important elements (namely nonlinear process project energy geostrophic adjustment calculations (Schubert calculations show local Rossby radius reduced from ambient value, tropical-storm-like vortices axisymmetric adjustment process becomes increasingly efficient at adjusting the wind the mass field this point of Rotunno and important processes underlying conceptual not, however, fundamentally at last school quite generally and does distinguish between it and describes the cooperative between convection and large-scale circulations is, in this school, Consequently, this school fails differentiate between (e.g. Hayashi 1970; Lindzen intensification. It distinguish between the roles of and surface fluxes the growing disturbance. may indeed defined in a sufficiently narrow however, when it better lends the metaphor of a influential road, detours perhaps, certainly not Closely linked ENB’s criticism is their assertion an important misconception in atmospheric science is the production energy’. They from two textbooks as evidence this misconception and remind us that the direct effect alter the available potential energy (APE); generated. ENB argue that in their theory WISHE) convection damps disturbances view of the tropics, which damping, is offered as a new The idea that disturbances in tropical-Pacific, has an observational basis that reference to. these observations the textbook quotes ENB call into question. They theories such as and deserve discussion. Latent-heat release cumulus convection early as the tropical storms (e.g. Riehl 1959). However, cold cores waves prevented the generalization result, as it was recognized that in convective heating would consume, rather section 1). Questions regarding nature of the energy source for the pioneering studies carried by the Tokyo UniversityKJniversity (Yanai, Nitta, University of Washington studies indicate that correlation between apparent heating temperature (i.e. low levels, the overall correlation is positive considerable range shown in Fig. which we have The same conclusion was reached in subsequent analyses 1958 and Marshall Island data (e.g. Nitta 1972, Fig. 19 and emphasize the earlier data, more recent earlier findings. instance, Hendon and (1994) use satellite data infer that during the amplification intraseasonal oscillation also analysed the result which is shown in the vertical and then The Coupled Ocean-Atmosphere Response Experiment the Tropical Global Atmosphere Vertical distribution of co-spectra representing the generation of eddy available potential energy which analyses Marshall Island sounding data from Vertical profile intensive observing period mean co-variance between temperature and vertical motion over intensive flux array Detailed information on and analysis methods is Lin and Johnson (1996). NOTES AND CORRESPONDENCE 1775 seen to be that observed by Wallace. not universal, however. For example, an analysis data suggests eastern tropical acts to observed disturbances 1977, section and Fig. 1979, Table exists an empirical basis tropical disturbances in the Exactly how comes about remains an open question. suggestion, advocated ENB, is describes the mechanism through waves generate, through the production anomalous enthalpy fluxes, the energy themselves against dissipation. a theory of eastward-propagating equatorially trapped waves (such as requires mean easterlies and predicts total surface fluxes leading quarter cycle. Recent observations data show that disturbances maintain themselves and propagate eastward mean westerlies, maxima in convection slightly leading surface winds and surface latent-heat fluxes (e.g. Lin Johnson 1996$). As (1996), the inability the theory explain these observations indicates that current further refinement. the equatorially trapped other modes (Emanuel 1993), are discussed in current observational 1; Thomspon 1979, Table 3). Although these observations not necessarily fatal the concept not bode well for particular models which date, been to explore Previous work indicates that difference between including those and most observed disturbances is the latter exhibit considerable vertical structure, and exist over sea surface varies substantially in space and Nakazawa 1995; and Johnson 1996). devote considerable space to For reasons that not clear, rename this concept QE, which continues twenty years after it was proposed (Arakawa and Schubert 1974). one form states that the cloud work function (which is closely related with time’ and that changes in active regimes. reconcile these assertions those shown in Fig. hundred Joules per kilogram more depending days? This of view tacit assumption that assertion that the changes in the CAPE are ‘small’ means that they small compared CAPE. In this is not what meant at Instead, the idea small compared with those would occur were somehow suppressed while the processes continued increase the with time. (following Arakawa and Schubert 1974): cloud work function, whose derivitive is partitioned, in between contributions closure is essentially scaling approximation in which (1) is neglected, on grounds that but of opposite sign. Observations satisfied. Consequently Atlantic Tropical Experiment. The Norquist because at upper levels in the combined region there be considerable between heating and temperature perturba- their budget over the ocean from which different analysis technique data set the signal removed, (1996) suggests fluxes lead convection these results are with explanations phase lead NOTES AND available potential energy running mean) the intensive during the intensive observing period. The solid and dashed lines represent air parcels originating from undergoing reversible pseudo adiabatic processes, respectively; ice effects are and Johnson (1996) for a data and analysis methods. changes in as those shown in Fig. not necessarily conflict with requires only that the variability of small compared what it would the absence of convection. was clearly stated Arakawa and Schubert, been clearly re-stated somehow misunderstandings second point is that, as already mentioned in the preceding paragraph, the mathematical formulation QE, as proposed division of the menagerie processes at work an atmospheric column into two As discussed Randall and (1993). such distinction cannot rigorously justified. For example, the stratiform clouds produced from deep often associated additional latent-heat release, precipitation, strong radiative effects. Should these considered as stratiform clouds are strongly coupled the convection, the other hand they have their own distinct life cycles may persist long after second example, surface fluxes sensible and latent heat promote convection, same time can be directly coupled convection through the action of convective thus difficult classify these fluxes as either unambiguously all processes as an important conceptual using strict closure in mass-flux representation of convection. (1993) showed that such is replaced by a prognostic closure based kinetic-energy equation, through is closely They argued that this an important advantage of prognostic closure, have endeavoured which we re-capitulate to some of the unclear, as over the years interpreted the acronym differently and, not surprisingly, different conclusions regarding its ENB’s point that early theories over-emphasize ambient conditional instability is important and well taken; nonetheless, as an . . lengthy dead-end . . . solely on this basis is particularly true which emphasized the importance surface fluxes tropical-storm intensification. played an important role in determining think about tropical and its interactions with large-scale circulations. Observations show latent heating is disturbances found in tropical western Pacific (i.e. they are not observations are explanations as Although Arakawa Schubert’s (1974) concept well supported the observations, does not the best their idea. comments notwithstanding, view of convecting systems. National Aeronautics and Space Administration Graduate Fellowships NGT-3023 1 acknowledges support Foundation (USA) (NSF) grant acknowledges support from NSF ONR from grant N00014-93-0456 as as enlightening discussions K. Ooyama, Shapiro and National Center for Atmospheric Research Mesoscale Microscale Meteorology seminar post-seminar discussions with this manuscript, as J. D. Neelin, Bretherton at school on moist convective processes. BS and are grateful Richard Johnson, whose wisdom improved this comment. Our seminar from the Dave Alexander, Ligia Bernardet, Mark Branson, Ching-Hsuan Chen, Robert Cifelli, Donald Dazlich, Charlotte DeMott, Ping Ding, Jensen, Hongli Jiang, Colin Jones, Michael Scott Rafkin, their collective insights greatly enriched discussions. The FORTRAN code used (as displayed in Fig. Emanuel (Massachucetts Institute and Eliassen, A. A., Neelin, and Salby, E. E. and and Rasmussen, cumulus cloud ensemble with the large-scale en- the hurricane depression. frictionally controlled meridional circulation the formation the atmosphere. 277-287 in time on WISHE modes. large-scale circulations convecting atmospheres. structure above the subtropics. large-scale equatorial heat and accelerating the zonal wind. thermodynamic characteristics over the warm pool TOGA COARE. atmosphere and Ed. Bert Intraseasonal oscillations during the TOGA-COARE generation and available potential in the Energy budget disturbances over ing the years disturbances observed during the study cyclone development. Numerical simulation the life cycle tropical cyclones. the theory and modeling linear CISK-models. cumulus parameteri- prognostic closure. Pp. and D. Reed, R. and Recker, E. and Emanuel, equatorial western Tropical meteorology. New York On production kinetic energy from condensation heating. atmosphere and sea Ed. Bert Linear analysis a tropical cyclone with increased interaction theory for tropical cyclones. Part Geostrophic adjustment an axisymmetric Wave-CISK and cumulus parameterization. Structure and properties the intertropical convergence zone eastern Atlantic. Spectral studies the tropical western Pacific. Geophys. Space Phys., Atmospheric intraseasonal variability the surface the tropical western Pacific Ocean.