Dynamical understandings of midlatitude transient eddy activity, especially its midwinter minimum over the North Pacific, are still limited, partly because Eulerian eddy statistics are incapable of separating cyclonic and anticyclonic contributions. Here we evaluate the two contributions separately based on local curvature of instantaneous flow fields to compare their seasonality between the North Pacific and North Atlantic storm-tracks. The anticyclonic contribution is found crucial for the midwinter minimum of the North Pacific transient eddy activity. Eddy energetics reveals that the net efficiency of the anticyclonic contribution in replenishing total transient eddy energy over the North Pacific exhibits a pronounced midwinter minimum, while that of the cyclonic counterpart does not in harmony with precipitation that peaks around midwinter. This study suggests that more attention should be paid to anticyclones in studying midlatitude storm-track dynamics.

Abstract The large scale tropical circulation, commonly named the Hadley circulation, is a key element in the global heat and moisture transport. Traditionally it is defined as the meridional circulation of the zonally averaged flow in the tropics, but in recent years studies have shown the importance of looking at the decomposition of the three-dimensional atmospheric flow into local meridional and zonal circulations. These studies gave useful analysis on the regionality and variability of the meridional circulation in different time scales, but were mostly limited to examining the regional strengthening/weakening of the circulation. Here we study the interannual variability of the longitudinally-dependent meridional circulation (LMC), with a focus on its zonal shift. We use hierarchical clustering to objectively determine the 5 main modes of the LMC interannual variability, and apply a Lagrangian air parcel tracking method to reveal the detailed patterns of the circulation. We find that the most prominent interannual variability of the LMC is an east-west shift, which plays a dominant role in the overall interannual variability of the tropical circulation. In addition, the LMC variability is found to be strongly related to other atmospheric variables such as the sea surface temperature, precipitation and air temperature. Using multiple linear regression we analyze these dependencies and discuss their implications for the tropical climate system. We also relate the LMC interannual variability to the Madden-Julian Oscillation (MJO) and find that the 2 La-Nina related modes are significantly correlated with 2 different MJO phases.

Clouds are primary modulators of Earth's energy balance. It is thus important to understand the links connecting variabilities in cloudiness to variabilities in other state variables of the climate system, and also describe how these links would change in a changing climate. A conceptual model of global cloudiness can help elucidate these points. In this work we derive simple representations of cloudiness, that can be useful in creating a theory of global cloudiness. These representations illustrate how both spatial and temporal variability of cloudiness can be expressed in terms of basic state variables. Specifically, cloud albedo is captured by a nonlinear combination of pressure velocity and a measure of the low-level stability, and cloud longwave effect is captured by surface temperature, pressure velocity, and standard deviation of pressure velocity. We conclude with a short discussion on the usefulness of this work in the context of global warming response studies.

Juno Microwave Radiometer (MWR) observations of Jupiter’s mid-latitudes reveal a strong correlation between brightness temperature contrasts and zonal winds, confirming that the banded structure extends throughout the troposphere. However, the microwave brightness gradient is observed to change sign with depth: the belts are microwave-bright in the p<5 bar range and microwave-dark in the p>10 bar range. The transition level (which we call the jovicline) is evident in the MWR 11.5 cm channel, which samples the 5-14 bar range when using the limb-darkening at all emission angles. The transition is located between 4 and 10 bars, and implies that belts change with depth from being NH3-depleted to NH3-enriched, or from physically-warm to physically-cool, or more likely a combination of both. The change in character occurs near the statically stable layer associated with water condensation. The implications of the transition are discussed in terms of ammonia redistribution via meridional circulation cells with opposing flows above and below the water condensation layer, and in terms of the ‘mushball’ precipitation model, which predicts steeper vertical ammonia gradients in the belts versus the zones. We show via the moist thermal wind equation that both the temperature and ammonia interpretations can lead to vertical shear on the zonal winds, but the shear is ~50x weaker if only NH3 gradients are considered. Conversely, if MWR observations are associated with kinetic temperature gradients then it would produce zonal winds that increase in strength down to the jovicline, consistent with Galileo probe measurements; then decay slowly at higher pressures.

The observed zonal winds at Jupiter’s cloud tops have been shown to be closely linked to the asymmetric part of the planet’s measured gravity field. However, other measurements suggest that in some latitudinal regions the flow below the clouds might be somewhat different from the observed cloud-level winds. Here we show, using both the symmetric and asymmetric parts of the measured gravity field, that the observed cloud-level wind profile between 25oS and 25oN must extend unaltered to depths of thousands of kilometers. Poleward, the midlatitude deep jets also contribute to the gravity signal, but might differ somewhat from the cloud-level winds. We analyze the likelihood of this difference and give bounds to its strength. We also find that to match the gravity measurements, the winds must project inward in the direction parallel to Jupiter’s spin axis, and that their decay inward should be in the radial direction.