Vertical structure and physical processes of the Madden-Julian Oscillation: Biases and uncertainties at short range

Abstract

An analysis of diabatic heating and moistening processes from 12 to 36 h lead time forecasts from 12 Global Circulation Models are presented as part of the "Vertical structure and physical processes of the Madden-Julian Oscillation (MJO)" project. A lead time of 12-36 h is chosen to constrain the large-scale dynamics and thermodynamics to be close to observations while avoiding being too close to the initial spin-up of the models as they adjust to being driven from the Years of Tropical Convection (YOTC) analysis. A comparison of the vertical velocity and rainfall with the observations and YOTC analysis suggests that the phases of convection associated with the MJO are constrained in most models at this lead time although the rainfall in the suppressed phase is typically overestimated. Although the large-scale dynamics is reasonably constrained, moistening and heating profiles have large intermodel spread. In particular, there are large spreads in convective heating and moistening at midlevels during the transition to active convection. Radiative heating and cloud parameters have the largest relative spread across models at upper levels during the active phase. A detailed analysis of time step behavior shows that some models show strong intermittency in rainfall and differences in the precipitation and dynamics relationship between models. The wealth of model outputs archived during this project is a very valuable resource for model developers beyond the study of the MJO. In addition, the findings of this study can inform the design of process model experiments, and inform the priorities for field experiments and future observing systems.

Keywords: Madden‐Julian Oscillation; Year of Tropical convection; convection; diabatic processes; modeling; uncertainties.

Figure 1

Hovmoller plot of TRMM 3B42 daily rainfall averaged between 10°S and 10°N to show the YoTC MJO cases E and F. Dotted black lines mark the approximate phase propagation. Blue horizontal line marks the longitudinal extend of the requested data domain from models. Red vertical line shows the range of consecutive days on which models are initialized for the two MJO cases. The range of days at the end of each 48 h forecast is marked in purple line. Hatched regions indicate the longitude extent of two 5°x5° domains marked A (75°–80°E, 0°–5°N) and B (95°–100°E, 10°S‐5°S) used to characterize the evolution of convection from a suppressed state to convective state.

Figure 2

Time step evolution of domain (75°–80°E, 0°–5°N) averaged precipitation as a function of forecast lead time for all the 22 forecasts for MJO case E. 48 h evolution of TRMM rainfall from each of the model initialization date are also shown as solid black line.

Figure 3

Time series of 12–36 h accumulated precipitation from models over 75°–80°E, 0°–5°N for MJO case E and 90°–95°E, 10°S–5°S for case F. Corresponding TRMM observations are shown as black line. Three phases of the convection in both panels are marked as suppressed, transition, and convective depending on the observed rainfall amounts.

Figure 4

Multimodel mean (solid lines) and standard deviation (whiskers) of zonal winds during (a) 0–24 h, (b) 12–36 h, and (c) 24–48 h into the forecasts.

Figure 5

Multimodel mean (solid lines) and standard deviation (whiskers) of ω during (a) 0–24 h, (b) 12–36 h, and (c) 24–48 h into the forecasts. d, e and f are similar plots for day 5, day 7, and day 12 leads from Component 3 of the experiments [Klingaman et al., 2015a], respectively. The corresponding analysis values are plotted as thick dashed line. Each color indicates different phases of the convection. Corresponding phases of the two MJO cases are combined in this figure.

Figure 6

The 12–36‐hourly biases of T, q, and RH with respect to YoTC analysis for all MJO phases based on both MJO cases. The thick black line is the multimodel mean bias.

Figure 7

Tendencies of specific humidity (a–c) due to convection, dynamics, and BL, microphysics, and diffusion combined during the 12–36 h forecasts. (d–f) The heating tendencies due to radiation, convection, dynamics, and BL, microphysics, and diffusion combined (BL + MP + D). Total tendencies are also shown. Multimodel means are plotted as solid lines and the range of model values (unlike the standard deviation in Figures 4 and 5 to span the full range of model behaviors) as whiskers. The tendencies from the ERA YoTC analysis is also plotted as dotted lines. Tendencies for suppressed (Figures 7a and 7d), transition (Figures 7b and 7e) and convective phases (Figures 7c and 7f) are shown. Please note the change of scale between panels.

Figure 8

Tendencies due to all the physics terms combined (convection, BL, microphysics, and diffusion) during the 12–36 h forecasts for the three convective phases for (a) moisture and (b) temperature. Intermodel spread is shown as whiskers around the multimodel mean (solid lines). The tendencies from the ERA YoTC analysis are shown as dotted lines.

Figure 9

The 12–36‐hourly total mass flux for the (a) suppressed, (b) transition, and (c) convective MJO phases. The dashed black line is the multimodel mean and the continuous black line is the YoTC data. Please note the change of scale between panels.

Figure 10

The 12–36‐hourly average profiles of heating tendency due to (a) total radiation (dT/dt _rad) and the contribution from (b) longwave and (c) shortwave radiation tendencies during convective phase. The dashed black line is the multimodel mean and the continuous black line is the YoTC data. Only the total tendency is available in the ERA YoTC data set and is plotted in Figure 10a).

Figure 11

The 12–36‐hourly profiles of (a) total cloud fraction, (b) cloud water, and (c) cloud ice for the convective phase. The dashed black line is the multimodel mean and the continuous black line is the YoTC data.

Figure 12

(a) RMS difference between consecutive time steps of rainfall averaged over 75°–80°E, 0°–5°N for MJO case E. The pattern correlations between rainfall and ω at all vertical levels over 50°–90°E, 10°S–10°N (a convective region) at every model time step initialized on 3 November 2009 are shown to highlight the contrasting behaviors of models with (b) strong (MetUM) and (c) weak (MIROC5) time step intermittency of rainfall.