Seasonal Characteristics and Interannual Variability of Monthly Scale Low-Frequency Oscillation in a Low-Order Global Spectral Model

Analysis is done of five-year low-pass filtered data by a five-layer low-order global spectral model, indicating that although any non-seasonal external forcing is not considered in the model atmosphere,monthly-scale anomaly takes place which is of remarkable seasonality and interannual variability.Analysis also shows that for the same seasonal external forcing the model atmosphere can exhibit two climatic states,similar in the departure pattern but opposite in sign, indicating that the anomaly is but the manifestation of the adverse states, which supports the theory of multi-equilibria proposed by Charney and Devore(1979) once again.Finally, the source for the low-frequency oscillation of the global atmosphere is found to be the convective heat source / sink inside the tropical atmosphere as discussed before in our study.Therefore, the key approach to the exploration of atmospheric steady low-frequency oscillation and the associated climatic effect lies in the examination of the distribution of convective heat sources / sinks and the variation in the tropical atmosphere.

South drying and north wetting over the Tibetan Plateau modulated by a zonal temperature dipole across timescales

Precipitation over the Tibetan Plateau and surrounding highlands is a crucial process in the hydrological cycle and is very important for local and downstream ecology,and previous research mainly focused on a certain range of timescales.A better understanding of the variability across various timescales,which has been largely ignored,can provide new insight on the regional weather and climate.Here,a north‒south dipole pattern of precipitation shaped by a zonal dipole of the upper-tropospheric temperature is revealed in this region.Both dipole patterns of the precipitation and the accompanied temperature exist from daily to interdecadal scales.The three-dimensional circulation anomalies connecting the temperature and precipitation dipoles are consistent across various timescales.The frequencies of daily events with opposite phases of the temperature dipole modulate the interannual and interdecadal variability in precipitation.The south drying and north wetting pattern over the Tibetan Plateau is an interdecadal manifestation of the precipitation dipole and can be ascribed to the temperature trend favourable for the positive phase of the zonal temperature dipole.The consistent dipole pattern constructs a more complete portrayal of precipitation over the Tibetan Plateau from synoptic scale to climatology.