The interaction between the collective effects of cumulus convection and large-scale dynamics is examined using the Betts–Miller moist convective adjustment (MCA) parameterization in a linearized primitive equation model on an equatorial β plane. In Part I of this paper, an analytical approach to the eigenvalue problem is taken using perturbation expansions in the cumulus adjustment time, which is short compared to planetary dynamical time scales. The modes of tropical variability that arise under MCA are dominated by the presence of moist processes; some modes act to adjust the system rapidly toward a convectively adjusted state, while others evolve on time scales set by the large-scale dynamics subject to near-adjusted (quasi equilibrium) thermodynamical constraints. Of the latter, a single vertical mode stands out, which obeys special balances implied by the quasi-equilibrium constraints and is the only propagating deep convective mode. The propagation speed is determined by an internally defined gross moist stability. For the Kelvin meridional mode, the phase speed and vertical structure are highly suggestive of those of the Madden–Julian (MJ) oscillation. For the simple case considered here, which assumes a homogeneous, separable basic state and sufficiently large zonal scales, the modes of variability found under MCA are all stable under reasonable conditions, although a large subclass of modes (including the MJ mode) is only slowly decaying. This contrasts with many studies using Kuo-like convective parameterizations, which have conjectured that convective instability of the second kind (CISK) plays a role in maintaining planetary-scale tropical variability. The authors suggest that a terminology is needed by which to refer to convective interaction with dynamics (CID), without necessarily assuming that large-scale instability arises from this interaction. Under MCA, there is strong CID but not generally CISK. Instability of the MJ mode can occur through evaporation–wind feedback. This behavior under MCA provides a suggestive prototype for tropical motions evolving under quasi-equilibrium convective constraints.

The interannual variability of the western North Pacific (WNP) summer monsoon is examined for the non-ENSO, ENSO developing, and ENSO decaying years, respectively. The ENSO developing (decaying) year is defined as the year before (after) the mature phase of ENSO, and the non-ENSO year is defined as the year that is neither the ENSO developing year nor the ENSO decaying year. A strong (weak) WNP summer monsoon tends to occur during the El Niño (La Niña) developing year and a weak (strong) WNP summer monsoon tends to occur during the El Niño (La Niña) decaying year. In all non-ENSO, ENSO developing, and ENSO decaying years, the strong (weak) WNP summer monsoon is associated with the positive (negative) rainfall anomalies, cold (warm) sea surface temperature anomalies, warm (cold) upper-tropospheric temperature anomalies, low (high) surface pressure anomalies, and a low-level cyclonic (anticyclonic) circulation anomaly over the subtropical WNP. The 850-hPa wave train associated with the WNP and east Asian (EA) summer monsoons in the non-ENSO, ENSO developing, and ENSO decaying years extends northward and suggests a possible teleconnection between the WNP summer monsoon and the North American climate. The wave train extended into the Southern Hemisphere in the non-ENSO and ENSO developing years implies a teleconnection between the WNP summer monsoon and the Australian winter climate. The anomalous WNP monsoon in the non-ENSO and ENSO developing years exists only in summer, while the anomalous WNP monsoon in the ENSO decaying year persists from the beginning of the year to the summer season. The anomalous WNP summer monsoon exhibits a strong ocean–atmosphere interaction, especially in the ENSO decaying year. This study suggests that the anomalous WNP summer monsoon in the non-ENSO year is associated with the variation of the meridional temperature gradient in the upper troposphere, while the anomalous WNP summer monsoon in the ENSO developing and decaying years is associated with ENSO-related SST anomalies.

Recent theoretical studies have indicated that large-scale circulation in deep convective regions evolves subject to an overall static stability—termed the gross moist stability—that takes into account both dry static stability and moist convective effects. The gross moist stability has been explicitly defined for a continuously stratified atmosphere under convective quasi-equilibrium constraints. A subsidiary quantity—the gross moisture stratification—measures the overall effectiveness in producing precipitation subject to these quasi-equilibrium constraints. These definitions are relevant in regions that experience deep convection sufficiently often; criteria based on climatological precipitation and maximum level of convection are used to define a domain of applicability. In this paper, 10-yr monthly mean rawinsonde data, and European Centre for Medium-Range Weather Forecasts (ECMWF) and National Meteorological Center (NMC) analyses are used to estimate the magnitude and horizontal distributio... Abstract Recent theoretical studies have indicated that large-scale circulation in deep convective regions evolves subject to an overall static stability—termed the gross moist stability—that takes into account both dry static stability and moist convective effects. The gross moist stability has been explicitly defined for a continuously stratified atmosphere under convective quasi-equilibrium constraints. A subsidiary quantity—the gross moisture stratification—measures the overall effectiveness in producing precipitation subject to these quasi-equilibrium constraints. These definitions are relevant in regions that experience deep convection sufficiently often; criteria based on climatological precipitation and maximum level of convection are used to define a domain of applicability. In this paper, 10-yr monthly mean rawinsonde data, and European Centre for Medium-Range Weather Forecasts (ECMWF) and National Meteorological Center (NMC) analyses are used to estimate the magnitude and horizontal distributio...

The potential links between ice water path (IWP), radiation, circulation, sea surface temperature (SST), and precipitation over the Pacific and Atlantic Oceans resulting from the falling ice radiative effects (FIREs) are examined from Coupled Model Intercomparison Project phase 5 (CMIP5) and phase 6 (CMIP6) historical simulations. The latter is divided into two subsets with (SON6) and without FIREs (NOS6) in CMIP6. Improvement in nonfalling cloud ice (~20 g m⁻²) is noticeable over convective regions in CMIP6 relative to CMIP5. The inclusion of FIREs in SON6 subset may contribute to reduce biases of overestimated outgoing longwave radiation and downward surface shortwave and underestimated reflected shortwave at the top of the atmosphere (TOA) by magnitudes of ~8 W m⁻² over convective regions against CERES, compared to NOS6 subset. The reduced biases in radiative fluxes in convective regions stabilize the atmosphere and lead to circulation, SST, cloud, and precipitation changes over the trade wind regions, as seen from improved radiative fluxes (~15 W m⁻²), surface wind stress biases, SST (~0.8 K), and precipitation (1 mm day⁻¹) biases. The significant improvement from NOS6 to SON6 leads to improved multimodel means for CMIP6 relative to CMIP5 for radiation fields over the trade wind regions but the degradation over convective zones is attributed to NOS6 subset. The results suggest that other sources of uncertainty and deficiencies in climate models may play significant roles for reducing discrepancies although FIREs, via radiation‐circulation coupling, may be one of the factors that help to reduce regional biases.

Convective interaction with dynamics (CID) dictates the structure and behavior of the eigenmodes of the tropical atmosphere under moist convective adjustment (MCA) when the convective adjustment time scale, τ_c, is much smaller than dynamical time scales, as examined analytically in Part I. Here, the modes are reexamined numerically to include the effects of finite τ_c, again for a primitive equation model with the Betts-Miller MCA parameterization. The numerical results at planetary scales are consistent with the analytical approach, with two well-separated classes of vertical modes: one subset evolves at the cumulus time scale, while the other subset evolves at a time scale set by the large-scale dynamics. All modes are stable for homogeneous basic states in the presence of simple mechanical damping effects. Thus, there is no CISK at any scale under MCA. However, the finite τ_c effect has the property of selectively damping the smallest scales while certain vertical modes at planetary scales decay only slowly. This planetary scale selection contrasts to many linear CISK studies, which tend to select the smallest scale. The Madden–Julian mode, which resembles the observed tropical intraseasonal oscillation, is found as a single vertical mode arising through Kelvin wave-CID. When the evaporation-wind feedback is included, this slowly decaying MJ mode is selectively destabilized at wavenumber one or two, consistent with the observations in the tropics. Stochastic forcing by nonresolved mesoscale processes can also potentially account for the existence of large-scale tropical variance. When the stochastic forcing occurs in the thermodynamic equation, the propagating deep-convective mode at planetary scales is the most strongly excited. Kinematic forcing excites slowly decaying kinematically dominated modes but cannot account for the characteristics of observed Madden-Julian variance.