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FIG. 2. Hovmdller diagrams of daily OLR (W m ’) from the two WRF experiments as well as NCEP-DOE reanalysis and NOAA-CPC interpolated observation. All are averaged between 7.5°S and 7.5°N. The lines on the panels represent speeds of 4m s_'.

Figure 2 Hovmdller diagrams of daily OLR (W m ’) from the two WRF experiments as well as NCEP-DOE reanalysis and NOAA-CPC interpolated observation. All are averaged between 7.5°S and 7.5°N. The lines on the panels represent speeds of 4m s_'.

Related Figures (13)

Fic. 1. Domain of the WRF simulations with precipitation from the NONUDGE experiment (mm day” ') averaged over the sim- ulation period (1 Oct 2007-31 Jan 2008). The latitudinal averaging in all subsequent figures is between 7.5°S and 7.5°N (dashed lines).
Fic. 1. Domain of the WRF simulations with precipitation from the NONUDGE experiment (mm day” ') averaged over the sim- ulation period (1 Oct 2007-31 Jan 2008). The latitudinal averaging in all subsequent figures is between 7.5°S and 7.5°N (dashed lines).
FiG. 3. Hovmiller diagram of daily zonal wind (ms~') at 850 hPa from the (a) NONUDGE and (b) GFDDA runs as well as (c) NCEP-DOE and (d) ERA-Interim reanalyses. All are averaged between 7.5°S and 7.5°N. The lines on the panels represent speeds of 4 m st
FiG. 3. Hovmiller diagram of daily zonal wind (ms~') at 850 hPa from the (a) NONUDGE and (b) GFDDA runs as well as (c) NCEP-DOE and (d) ERA-Interim reanalyses. All are averaged between 7.5°S and 7.5°N. The lines on the panels represent speeds of 4 m st
evolution of a variable during the MJO life cycle, one has to produce a composite. Even though it is well doc- umented that the MJO structure shows variations as it propagates eastward across the Maritime Continent (Kiladis et al. 2005), we neglect these variations in favor of constructing a robust composite MJO using the entire ongitudinal model domain for the purpose of obtaining first-order understanding of its thermodynamics. Thus, the underlying assumptions in the composite analysis are that the MJO propagates at a constant speed over the longitudinal domain of the model and there are no
evolution of a variable during the MJO life cycle, one has to produce a composite. Even though it is well doc- umented that the MJO structure shows variations as it propagates eastward across the Maritime Continent (Kiladis et al. 2005), we neglect these variations in favor of constructing a robust composite MJO using the entire ongitudinal model domain for the purpose of obtaining first-order understanding of its thermodynamics. Thus, the underlying assumptions in the composite analysis are that the MJO propagates at a constant speed over the longitudinal domain of the model and there are no
FIG. 5. (a) First and (b) second EOFs of OLR from the two simulations and NOAA-CPC interpolated data. (c) MJO index and (d) cross correlation of the associated principal components. inherent differences among the longitudinal and tem- poral points other than the differences in the phases of the MJO. In other words, suppose a particular phase of the MJO, say peak precipitation (pcp), is observed at points (t,,x,) and (t,,x,). Then the MJO is propagating at speed c = (x, — x,)/(t, — t,). Therefore, from a refer- ence frame of a hypothetical point x, that moves at the phase speed of the MJO, the variable (precipitation in this case) is pcp’(¢,x,) = pep[t,x, + c(t — t,)]. This trans- formation essentially compresses the hundreds of snap- shots of the MJO from the entire longitudinal domain into a 4-month-long time series from a single (hypo- thetical) point. The reference point (t,,x,) is taken to be 14 October and 63°E. Figure 6 shows the evolution of precipitation, convective latent heating, and per- turbation potential temperature from the reference frame of a point moving with the MJO atc =4ms |. The two MJO peak precipitation times are on days 34 and 81 and are marked by the dashed vertical lines. These ines also more or less coincide with the peak heating, which is also in phase with the positive perturbation
FIG. 5. (a) First and (b) second EOFs of OLR from the two simulations and NOAA-CPC interpolated data. (c) MJO index and (d) cross correlation of the associated principal components. inherent differences among the longitudinal and tem- poral points other than the differences in the phases of the MJO. In other words, suppose a particular phase of the MJO, say peak precipitation (pcp), is observed at points (t,,x,) and (t,,x,). Then the MJO is propagating at speed c = (x, — x,)/(t, — t,). Therefore, from a refer- ence frame of a hypothetical point x, that moves at the phase speed of the MJO, the variable (precipitation in this case) is pcp’(¢,x,) = pep[t,x, + c(t — t,)]. This trans- formation essentially compresses the hundreds of snap- shots of the MJO from the entire longitudinal domain into a 4-month-long time series from a single (hypo- thetical) point. The reference point (t,,x,) is taken to be 14 October and 63°E. Figure 6 shows the evolution of precipitation, convective latent heating, and per- turbation potential temperature from the reference frame of a point moving with the MJO atc =4ms |. The two MJO peak precipitation times are on days 34 and 81 and are marked by the dashed vertical lines. These ines also more or less coincide with the peak heating, which is also in phase with the positive perturbation
FIG. 6. Composites of (a) precipitation (mm day~'), (b) convective latent heating (K day™'), and (c) potential temperature perturbations (K).
FIG. 6. Composites of (a) precipitation (mm day~'), (b) convective latent heating (K day™'), and (c) potential temperature perturbations (K).
FIG. 7. Composite of sources and sinks of eddy available potential energy (K* day™').
FIG. 7. Composite of sources and sinks of eddy available potential energy (K* day™').
Fic. 10. Downward and upward transport of EAPE (K? day~').
Fic. 10. Downward and upward transport of EAPE (K? day~').
Fic. 9. Zonal, meridional, and vertical parts of the conversion to EAPE (K? day ') averaged between (a) the surface and the tran- sition level (solid curve in Fig. Sd) and 200 hPa, and (b) 200 hPa and the transition level.
Fic. 9. Zonal, meridional, and vertical parts of the conversion to EAPE (K? day ') averaged between (a) the surface and the tran- sition level (solid curve in Fig. Sd) and 200 hPa, and (b) 200 hPa and the transition level.
step is to identify the roles of the upward and downward components of this transport. EAPE could be generated at the surface (e.g., by variation in SST) and transported upward or it could be generated in the upper troposphere and advected downward by subsidence to force shallow convection. Figure 10 shows the contributions of the upward and downward parts of this vertical transport. The downward component oscillates up and down with the MJO cycle as the transition line does to a lesser extent. The oscillation in the upward component is less apparent. The triggering of deep heating is followed by subsidence that coincides with a temperature mini- mum. The subsidence of cold air, presumably asso- ciated with mesoscale downdrafts, at the low levels gradually retreats upward until the convective damping layer is deep enough for the next MJO deep heating to be triggered.
step is to identify the roles of the upward and downward components of this transport. EAPE could be generated at the surface (e.g., by variation in SST) and transported upward or it could be generated in the upper troposphere and advected downward by subsidence to force shallow convection. Figure 10 shows the contributions of the upward and downward parts of this vertical transport. The downward component oscillates up and down with the MJO cycle as the transition line does to a lesser extent. The oscillation in the upward component is less apparent. The triggering of deep heating is followed by subsidence that coincides with a temperature mini- mum. The subsidence of cold air, presumably asso- ciated with mesoscale downdrafts, at the low levels gradually retreats upward until the convective damping layer is deep enough for the next MJO deep heating to be triggered.
Fic. 11. Perturbation of moistening by the observational nudging term (g kg! day !).
Fic. 11. Perturbation of moistening by the observational nudging term (g kg! day !).
Fic. 13. Simplified paradigm of the EAPE cycle in the model MJO. The dashed line represents the time of peak precipitation.
Fic. 13. Simplified paradigm of the EAPE cycle in the model MJO. The dashed line represents the time of peak precipitation.
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ThermodynamicsAtmospheric sciencesMadden Julian Oscillation
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