Three transient National Center for Atmospheric Research Community Climate System Model, version 3 model simulations were analyzed to study the responses of El Niño–Southern Oscillation (ENSO) and the equatorial Pacific annual cycle (AC) to external forcings over the last 300,000 years. The time‐varying boundary conditions of insolation, greenhouse gases, and continental ice sheets, accelerated by a factor of 100, were sequentially added in these simulations. The simulated ENSO and AC amplitudes change in phase, and both have pronounced precession band variance (~21,000 years). The precession‐modulated slow (orbital time scales) ENSO evolution is dominated linearly by the change of the coupled ocean‐atmosphere instability, notably the Ekman upwelling feedback and thermocline feedback. In contrast, the greenhouse gases and ice sheet forcings (~100,000‐year cycles) are opposed to each other as they influence ENSO variability through changes in AC amplitude via a common nonlinear frequency entrainment mechanism. The acceleration technique could dampen and delay the precession signals below the surface ocean associated with ENSO intensity.

A technique to estimate tropical cyclone (TC) current intensity based on geostationary satellite infrared window (IRW) and water vapor (WV) imagery is explored in this paper. First, to combine the advantages of the IRW imagery and the WV minus IRW (WV-IRW) imagery, a WV-IRW-to-IRW ratio (WIRa)-based indicator is proposed. This indicator not only can display the inner-core convection's symmetrization level and vigor but also is able to screen out thin cirrus, stratospheric WV anomaly, and overshooting tops from average deep convection. It is highly correlated with the best track minimum sea-level pressure and thus used to estimate the western North Pacific TC current intensity. Detailed analyses have demonstrated that the WIRa-based indicator can further improve the estimation of TC current intensity alongside the existing algorithms. The WIRa-based indicator is designed based on the hypothesis that “overshooting top is more useful for forecasting than initial estimation,” and the satisfying results of the WIRa-based method perhaps provide indirect evidence to support this hypothesis in turn.

The temporal and spatial slopes of water isotope‐temperature relations are studied for the last 21,000 years over the middle and high latitudes using a series of snapshot simulations of global climate and water isotopes in the isotope‐enabled atmospheric model isoCAM3. Our model simulation suggests that both the temporal slope and spatial slope remain largely stable throughout the last deglaciation. Furthermore, the temporal slope can vary substantially across regions. Nevertheless, on average, and most likely, the temporal slope is about 0.3‰ °C⁻¹ and is about half of the spatial slope. Finally, the relation between temporal and spatial slopes is understood using a semiempirical equation that is derived based on both the Rayleigh distillation and a fixed spatial slope. The slope equation quantifies the Boyle's mechanism and suggests that the temporal slope is usually smaller than the spatial slope in the extratropics mainly because of the polar amplification feature in global climate change, such that the response in local temperature at middle and high latitudes is usually greater than that in the total equivalent source temperature.

Water isotopes in precipitation have played a key role in the reconstruction of past climate on millennial timescales and longer. However, for midlatitude regions like East Asia with complex terrain, the reliability behind the basic assumptions of the temperature effect and amount effect is based on modern observational data and still remains unclear for past climate. In the present work, we reexamine the two basic effects on seasonal, interannual, and millennial timescales in a set of time slice experiments for the period 22–0 ka using an isotope-enabled atmospheric general circulation model (AGCM). Our study confirms the robustness of the temperature and amount effects on the seasonal cycle over China in the present climatic conditions, with the temperature effect dominating in northern China and the amount effect dominating in the far south of China but no distinct effect in the transition region of central China. However, our analysis shows that neither temperature nor amount effect is significantly dominant over China on millennial and interannual timescales, which is a challenge to those classic assumptions in past climate reconstruction. Our work helps shed light on the interpretation of the proxy record of δ¹⁸O from a modeling point of view.

Stable water isotopologues in paleoclimate archives ( ${\mathsf{\delta }}^{18}\mathrm{O}$ ) have been widely used as an indicator to derive past climate variations. The modern observed spatial ${\mathsf{\delta }}^{18}\mathrm{O}$ -temperature relation in the middle and high latitudes has been used to infer the paleotemperatures changes from ice core data. However, various studies have shown that the spatial slope is larger than the temporal slope at the drill site by a factor of 2. Physically, the different spatial and temporal slope has been suggested to result from the amplified local surface air temperature cooling in the polar region at Last Glacial Maximum (LGM), according to the slope ratio equation derived in our previous study. To explicitly confirm the “polar amplification” effect in understanding the differences between temporal and spatial isotope–temperature relations, here we use the same isotope-enabled atmospheric general circulation model with a moisture-tracing module embedded to quantitatively estimate the contributions of different sources to the precipitated heavy oxygen isotopes in the middle and high latitudes. Our results show that the major sources of ${\mathsf{\delta }}^{18}\mathrm{O}$ in precipitation over middle and high latitudes are from oceans where the sea surface temperature cooling at Last Glacial Maximum (LGM) is less than −2 $°\mathrm{C}$ , while the local moisture sources with a higher cooling can be also relevant for polar regions, such as north Greenland. Additionally, the neglect of the strengthened local inversion layer strength at LGM could be the main cause for the overestimated source temperature cooling by the slope ratio equation, especially for the polar regions in the Northern Hemisphere.