The Green's function model intercomparison project (GFMIP) protocol

The atmospheric Green's function method is a technique for modeling the response of the atmosphere to changes in the spatial field of surface temperature. While early studies applied this method to changes in atmospheric circulation, it has also become an important tool to understand changes in radiative feedbacks due to evolving patterns of warming, a phenomenon called the “pattern effect.” To better study this method, this paper presents a protocol for creating atmospheric Green's functions to serve as the basis for a model intercomparison project, GFMIP. The protocol has been developed using a series of sensitivity tests performed with the HadAM3 atmosphere‐only general circulation model, along with existing and new simulations from other models. Our preliminary results have uncovered nonlinearities in the response of the atmosphere to surface temperature changes, including an asymmetrical response to warming versus cooling patch perturbations, and a change in the dependence of the response on the magnitude and size of the patches. These nonlinearities suggest that the pattern effect may depend on the heterogeneity of warming as well as its location. These experiments have also revealed tradeoffs in experimental design between patch size, perturbation strength, and the length of control and patch simulations. The protocol chosen on the basis of these experiments balances scientific utility with the simulation time and setup required by the Green's function approach. Running these simulations will further our understanding of many aspects of atmospheric response, from the pattern effect and radiative feedbacks to changes in circulation, cloudiness, and precipitation

Mitochondrial DNA Evidence for a Diversified Origin of Workers Building Mausoleum for First Emperor of China

Variant studies on ancient DNA have attempted to reveal individual origin. Here, based on cloning sequencing and polymerase chain reaction-restriction fragment length polymorphisms, we analyzed polymorphisms in the first hypervariable region and coding regions of mitochondrial DNA of 19 human bone remains which were excavated from a tomb near the Terra Cotta Warriors and dated some 2,200 years before present. With the aim of shedding light on origins of these samples who were supposed to be workers building the mausoleum for the First Emperor of China, we compared them with 2,164 mtDNA profiles from 32 contemporary Chinese populations at both population and individual levels. Our results showed that mausoleum-building workers may be derived from very diverse sources of origin

Connections between the QBO and Tropical Variability

Troposphere-stratosphere dynamic coupling plays a crucial role in short and long term forecasts. In the tropics, the quasi-biennial oscillation (QBO) dominates stratospheric variability with zonal mean zonal wind alternating between westerly and easterly for an average period of 28 months. It has been shown in previous studies that the QBO can affect the tropical troposphere in different ways. Easterly phases of the QBO lead to stronger tropical deep convection in both observations and model simulations. Recent studies have indicated that activities of the Madden-Julian Oscillation (MJO) in boreal winter are also stronger in easterly phases of the QBO than its westerly phases. The MJO is one major component of the tropical intraseasonal variability and it is a key factor in bridging weather and climate. This QBO-MJO connection is of great importance for the following reasons: (1) Prediction of a single MJO event still suffers from many problems in most forecast models; (2) The QBO can be predicted more easily, thus there is large room for prediction improvement if the QBO-MJO connection is fully understood. In this study, a precipitation tracking method is used to identify individual MJO events, along with analysis of traditional Empirical Orthogonal Function (EOF) based global MJO indices that are independent of the tracking method. The results show that stronger MJO activities in QBO easterly phases are a consequence of more MJO days, not larger amplitudes of individual MJO events as previously thought. More MJO days come from more MJO events initiated over the Indian Ocean and their longer duration because of a weaker barrier effect of the Maritime Continent on MJO propagation. In addition, responses of general convective signals (e.g., total precipitation and cloud coverage) and tropical waves (Kelvin wave, Rossby wave and Mixed Rossby-Gravity wave) to QBO are also investigated in this study. The QBO-total precipitation connection shows both seasonal and spatial variations. Diversity among these responses reveals complexity in connections between the QBO and tropical variability of different scales. Physical processes behind theses connections are thus strongly demanded, and potential ones are discussed in this study

The Role of Radiative Interactions in Organized Convective Systems

Accurate simulations of the coupling between radiation, clouds and the circulation in general circulation models (GCMs) play an important role in governing the frequency and intensity of convection and the hydrological cycle. We investigate radiative feedbacks associated with the Madden-Julian Oscillation (MJO) using radiative kernels. We find that changes in clouds, compared to&nbsp; those in temperature, water vapor and albedo, induce the largest radiative perturbations during active phases of the MJO. Strong radiative heating helps the MJO survive the barrier effect of the Maritime Continent. To examine how radiation affects the development of organized convective systems under realistic boundary conditions, a series of mechanism-denial experiments are conducted in a high-resolution GCM where synoptic-scale interactions between radiation and convection are disabled. When radiative interactions are suppressed, the global TC frequency is reduced, which is primarily due to a decrease in the frequency of pre-TC synoptic disturbances, whereas the likelihood that the disturbances undergo cyclogenesis is less affected. TC duration is also reduced because TC genesis locations are shifting toward coastal regions when radiative interactions are suppressed. In a warmer climate, the magnitude of the reduction in TC frequency is diminished due to greater contribution from latent heat release with increased sea surface temperatures. Suppressing radiative interactions also reduces the spatial contrast in radiative cooling from dry to moist regions and thus the upgradient transport of moist static energy, resulting in a reduction in the degree of aggregation and extreme precipitation events at regional scales. Based on an ensemble of state-of-the-art GCMs, we find that the spatial patterns of future precipitation change exhibit a strong dependence on the current climate. Therefore, models can be screened using observations as a constraint to reduce the intermodel spread in projections of future climate change.</p

Constraining Climate Model Projections of Regional Precipitation Change

As communities prepare for the impacts of climate change, policy makers and stakeholders increasingly require locally resolved projections of future climate. Statistical downscaling uses low‐resolution outputs from climate models and historical observations to both enhance the spatial resolution and correct for systematic biases. By examining the downscaled rainfall over land, we show that although bias corrections are effective in reducing biases in the current climate, they do not reduce the intermodel spread in future rainfall projections. This failure stems from the strong dependence of future rainfall change upon the current climatological rainfall patterns. Even after bias corrections are applied, the downscaled projections of precipitation change retain this dependence upon their native climatology. However, we show that this dependence can be exploited; even very simple methods to subset models according to their ability to resolve the observed rainfall climatology can substantially reduce the intermodel spread in rainfall projections. Plain Language Summary To prepare for future climate change, policy makers and stakeholders require reliable model projections with high spatial resolution. To meet this need, statistical methods have been developed to postprocess the model output so correct for systematic biases and enhance the spatial resolution. We focus on rainfall over land and find that the postprocessing only yields consistent values for the current climate and no reduction in the uncertainty is obtained for future projections even after the postprocessing. We show that patterns of future rainfall change exhibit a strong dependence on the current climate. This dependence can be exploited by selecting models based on their ability to reproduce the observed climate. We show that this screening of models can significantly reduce the uncertainty in future rainfall projections. The success of this simple method emphasizes the importance of model evaluation in reducing the uncertainty of multimodel climate change projections. Key Points Statistical downscaling improves the current climatology but does not reduce the intermodel spread of future rainfall projections Models with more similar base climates yield more similar projections of change both with and without statistical downscaling Screening models provides a simple method for constraining future projections and is insensitive to the choice of observational data set

Radiative Feedbacks Associated with the Madden–Julian Oscillation

Abstract Radiative kernels derived from CloudSat/CALIPSO measurements are used to diagnose radiative feedbacks induced by the Madden–Julian oscillation (MJO). Over the Indo-Pacific warm pool, positive cloud and water vapor feedbacks are coincident with the convective envelope of the MJO during its active phases, whereas the lapse rate feedback shows faster eastward propagation than the convective envelope. During phase 2/3, when the convective envelope is over the Indian Ocean, water vapor exhibits a vertically coherent response, with the largest anomalies and strongest feedback in the midtroposphere. Though spatial structures of the feedbacks vary, the most prominent difference lies in the magnitude. Cloud changes induce the largest radiative perturbations associated with the MJO. It is also found that the strength of the cloud feedback per unit of precipitation is greater for strong MJO events, suggesting that the strength of individual MJO events is largely dictated by the magnitude of cloud radiative heating of the atmosphere. In addition, stronger radiative heating due to water vapor and clouds helps the MJO survive the barrier effect of the Maritime Continent, leading to farther eastward propagation. These results offer process-oriented metrics that could help to improve model simulations and predictions of the MJO in the future

Study on the effect of the pressure characteristics of the cone throttle on the cavitation

According to the cone-type throttle valve is prone to cavitation, resulting in the reduction in the performance of the cone throttle valve. Here, a visual experimental platform for hydraulic cavitation is built, and the cavitation number of the conical throttle valve under different working pressure, opening degree, and different back pressure is studied. The cavitation image under different conditions is obtained. The research shows that properly increasing back pressure, reducing system working pressure, and keeping small opening of the valve port can restrain cavitation

A Vertically Resolved Analysis of Radiative Feedbacks on Moist Static Energy Variance in Tropical Cyclones

Abstract A vertically resolved moist static energy (MSE) variance budget framework is used to diagnose processes associated with the development of tropical cyclones (TCs) in a general circulation model (GCM) under realistic boundary conditions. Previous studies have shown that interactions between radiation and MSE promotes TC development. Here we examine the vertical contributions of radiation and its interactions with MSE by performing several mechanism-denial experiments in which synoptic-scale radiative interactions are suppressed either in the boundary layer or in the free troposphere. Partly suppressing radiative interactions result in a reduction in global TC frequency. However, the magnitude of reduction and structure of the feedback depend on the intensity and structure of the TCs in these mechanism-denial experiments, indicating that both the magnitude and the vertical location of radiative interactions can impact global TC frequency. Using instantaneous 6-houly outputs, an explicit computation reveals distinct spatial patterns of the advection term: the vertical component is positive in the mid to upper troposphere that reflects an upward transport of MSE by deep convection, whereas the horizontal component is positive in the boundary layer. These results illustrate the impact of the vertical distribution of radiative interactions and vertically varied contribution of the advection term in the development of TCs

Enhanced hydrological cycle increases ocean heat uptake and moderates transient climate change

The large-scale moistening of the atmosphere in response to increasing greenhouse gases amplifies the existing patterns of precipitation minus evaporation (P-E) which, in turn, amplifies the spatial contrast in sea surface salinity (SSS). Through a series of transient CO(2) doubling experiments, we demonstrate that surface salinification driven by the amplified dry conditions (P-E < 0), primarily in the subtropical ocean, accelerates ocean heat uptake. The salinification also drives the sequestration of upper-level heat into the deeper ocean, reducing the thermal stratification and increasing the heat uptake through a positive feedback. The change in Atlantic Meridional Overturning Circulation due to salinification plays a secondary role in heat uptake. Consistent with the heat uptake changes, the transient climate response would increase by approximately 0.4 K without this process. Observed multi-decadal changes in subsurface temperature and salinity resembles those simulated, indicating that anthropogenically-forced changes in salinity are likely enhancing the ocean heat uptake