Analitički model ekvatorijalnih valova uz konvekcijsku raspoloživu potencijalnu energiju i vlagu

The convective available potential energy (CAPE) closure and the moisture closure is implemented on an analytical linearized model for large-scale motions. The model includes cloud-radiation interaction (CRI), gross moist stability and wind-induced surface heat exchange (WISHE). The model is done in an equatorial non-rotating atmosphere and is vertically resolved. As the gravity waves in non-rotating atmosphere map to Kelvin waves in rotating atmosphere, the modeled modes are fast Kelvin waves that resemble adiabatic modes, convectively coupled Kelvin modes that are damped and move with the observed phase speed of 17 ms–1 and the unstable slow moisture mode. The slow moisture mode owes its propagation speed to WISHE and instability to CRI and gross moist instability. It is thought that it can be related to the easterly waves and perhaps even the Madden-Julian oscillation (MJO).Na analitički linearni model za dugoperiodičke valove implementirana je ovisnost oborina o konvekcijskoj raspoloživoj potencijalnoj energiji i vlazi kojom se promatra povezanost konvekcije i valova. Model također uključuje međudjelovanje oblaka i zračenja, osnovnu vlažnu nestabilnost i površinsku izmjenu topline uzrokovanu vjetrom. Model je primijenjen na ekvatorijalnoj ne-rotirajućoj atmosferi i uključuje ovisnost modeliranih polja po vertikali. Težinski valovi u ne-rotirajućoj atmosferi su ekvivalentni Kelvinovim valovima u rotirajućoj atmosferi. Modelirani valovi su brzi stabilni adijabatski Kelvinovi valovi, stabilni Kelvinovi valovi povezani s konvekcijom koji propagiraju faznom brzinom od 17 ms–1 i nestabilni vlažni val male fazne brzine. Vlažni val propagira radi površinske izmjene topline uzrokovane vjetrom, a nestabilan je radi međudjelovanja oblaka i zračenja i osnovne vlažne nestabilnosti. Moguće je da vlažni val predstavlja jedan od mehanizama za tropske istočne valove i Madden-Julian oscilaciju

Large-Scale Modes of the Tropical Atmosphere. Part I: Analytical Modeling of Convectively Coupled Kelvin Waves Using the Boundary-Layer Quasiequilibrium Approximation

One way of modeling the convectively coupled Kelvin waves in an equa­to­rial non-rotating atmosphere is presented. It implements a simple linear, analytical model using the boundary-layer quasiequilibrium approximation and wind-induced surface heat exchange. The dynamics of the model are based on the assumption that the vertical heating profile has the shape of the first baroclinic mode. The vertical velocity has two sinusoidal components of different vertical wavelengths. One component corresponds to deep convec­tion and the imposed heating profile while the other component, with shal­lower vertical wavelength, defines the phase speed of the convectively coupled Kelvin wave. The results of the model show fast Kelvin waves that resemble adiabatic modes with the vertical wavelength being twice the depth of the troposphere and convectively coupled Kelvin waves that are damped and propagate with phase speed of 18 m/s. Wind-induced surface heat exchange causes the in­sta­bility of the convectively coupled Kelvin waves, but only for very long wave­lengths. The value of the model is that under the single dynamical assumption of the vertical heating profile and using the boundary-layer quasiequilibrium assumption it yields the observed phase speed for the convectively couple Kelvin waves.U radu se prezentira jedan način modeliranja konvektivno združenih Kelvinovih valova u ekvatorijalnoj nerotirajućoj atmosferi. Ono uključuje jednostavni linearni, analitički model koristeći kvaziravnotežnu aproksimaciju u graničnom sloju i površinsku izmjenu topline uzrokovanu vjetrom. Dinamika modela temelji se na pretpostavci da vertikalni profil grijanja ima oblik prvog baroklinog moda. Vertikalna brzina ima dvije sinusoidalne komponente različitih vertikalnih valnih duljina. Jedna odgovara dubokoj konvekciji i nametnutom profilu zagrijavanja, dok druga komponenta kraće vertikalne valne duljine definira faznu brzinu konvektivno zdru`enog Kelvinovog vala. Rezultati modela su brzi Kelvinovi valovi koji sliče adijabatskim modovima s vertikalnom valnom duljinom dvostruko većom od dubine troposfere i konvektivno združenih Kelvinovih valova koji su prigušeni i propagiraju faznom brzinom od 18 m/s. Površiinska izmjena topline uzrokovana vjetrom čini konvektivno združene Kelvinove valove nestabilnim samo za vrlo duge valove. Vrijednost modela je u tome da pod jednostavnom pretpostavkom vertikalnog profila grijanja i kori{tenjem kvaziravnotežne aproksimacije graničnog sloja daje opaženu faznu brzinu konvektivno združenih Kelvinovih valova

Dugoperiodički modovi u tropskoj atmosferi Drugi dio: Analitičko modeliranje Kelvinovih valova povezanih s konvekcijom uz konvekcijsku raspoloživu potencijalnu energiju

The thermal assumption of the model is based on the convective available potential energy (CAPE) closure, i.e. increased CAPE, represented by decreased midlevel potential temperature, results in increased precipitation. The dynamic assumption of the model is that the vertical heating profile has the shape of the first baroclinic mode, while the vertical dependence of modeled fields is calculated, i.e. the model is vertically resolved. The modeled modes are free Kelvin waves and convectively coupled Kelvin waves. It is shown that the CAPE closure is not sufficient to produce the observed destabilization of the Kelvin mode, but that the dynamical properties of the model give the observed phase speeds.Termalna pretpostavka modela je da konvekcijski raspoloživa potencijalna energija utječe na količinu oborine. Konvekcijski raspoloživa potencijalna energija ovisi o potencijalnoj temperaturi u srednjoj troposferi. Uzrok povećane količine oborine je smanjena potencijalna temperatura u srednjoj troposferi. Dinamika modela je razvijena uz pretpostavku da vertikalni profil grijanja ima oblik prvog baroklinog moda dok se u modelu računa ovisnost termodinamičkih polja po vertikali. Modelirani valovi su slobodni Kelvinovi valovi i Kelvinovi valovi povezani s konvekcijom. Iz modela se vidi da konvekcijski raspoloživa potencijalna energija nije dovoljna za opaženu nestabilnost Kelvinovih valova povezanih s konvekcijom, ali dinamika modela daje opaženu faznu brzinu

Konvektivno udruženi Kelvinovi valovi i konvektivna inhibicija

We use a thermodynamic assumption that the vertical heating profile has the shape of the first baroclinic mode, and that the analytical expression for vertical velocity has two modes, representing shallow and deep convection. The thermal assumption of the model is given through the convective inhibition closure, i.e. negative convective inhibition results in increased precipitation. These modeled modes are the free Kelvin waves and the convectively coupled Kelvin waves. We find the latter mode to be unstable, with maximum growth rate at wavelengths of 6 000 kilometers. The model successfully captures the observed nature of the Kelvin waves and shows that convective inhibition closure is sufficient to trigger the observed destabilization of the convectively coupled Kelvin mode.Termodinamičke pretpostavke modela uključuju vertikalni profil grijanja koji ima oblik prvog baroklinog moda. Pretpostavljeni oblik vertikalne brzine sastoji se od dva dijela koji odgovaraju plitkoj i dubokoj konvekciji. Za parametrizaciju oborine uzeta je negativna konvektivna inhibicija (CIN). Dobiveni modovi su slobodni Kelvinovi valovi i Kelvinov val povezan s konvekcijom. Kelvinov val povezan s konvekcijom je nestabilan, a najveću nestabilnost pokazuje pri valnoj duljini od 6 000 km. Ovim modelom uspješno je reproducirana opažena priroda Kelvinovih valova, a iz modela se vidi da je konvektivna inhibicija dovoljna za modeliranje opažene nestabilnosti Kelvinovih valova povezanih s konvekcijom

The Mechanics of Gross Moist Stability

The gross moist stability relates the net lateral outflow of moist entropy or moist static energy from an atmospheric convective region to some measure of the strength of the convection in that region. If the gross moist stability can be predicted as a function of the local environmental conditions, then it becomes the key element in understanding how convection is controlled by the large‐scale flow. This paper provides a guide to the various ways in which the gross moist stability is defined and the subtleties of its calculation from observations and models. Various theories for the determination of the gross moist stability are presented and its roles in current conceptual models for the tropical atmospheric circulation are analyzed. The possible effect of negative gross moist stability on the development and dynamics of tropical disturbances is currently of great interest