Extratropical influences on tropical sea surface temperature (SST) have implications for decadal predictability. We implement a cloud‐locking technique to highlight the critical role of clouds in ...shaping the tropical SST response to extratropical thermal forcing. With heating imposed over either the extratropical Northern Atlantic or Pacific, Hadley Cells respond similarly that the trades strengthen south of the rainband. The wind‐evaporation‐SST (WES) feedback leads to cooling over the southern subtropics, which is enhanced in the southeastern Pacific due to the positive feedback between SST and stratiform clouds. Cloud‐locking experiments show that zonal contrasts in SST and cloud feedbacks in the Pacific enhance the zonal surface winds, leading to increased evaporation and strengthens zonal SST difference. We propose that the meridional and zonal SST gradients are tightly linked via WES effects and the cloud‐radiative‐SST feedbacks, which are largely determined by the climatological rainband position and the spatial distribution of cloud properties.
Plain Language Summary
Tropical Pacific sea surface temperature (SST) plays a key role in climate variability around the globe. Understanding how tropical Pacific SST can be impacted by climate perturbation at mid‐to‐high latitudes is essential for improving climate prediction skills. In this study, how clouds modulate such interaction between tropics and extratropics is examined by utilizing global climate model simulations. With idealized heating being imposed in either the extratropical Northern Atlantic or Pacific, we found common response patterns in the tropical Pacific to the heating. Two factors shape the common response patterns. First, the anomalous southerly winds act to enhance or weaken the evaporative cooling, depending on the climatological rainband position and the associated trade wind directions. Secondly, the anomalous SST induced by changes in evaporation is either amplified or damped by cloud cover changes, since the relationships between SST and cloud amount depend on cloud types. A series of physical processes, which are largely established by the mean‐state climate pattern, act to link the zonal and meridional structure of the SST over the tropical Pacific.
Key Points
Tropical surface temperature responds similarly to idealized heating imposed over either North Atlantic or North Pacific as fast response
Clouds are essential in forming the tropical response pattern through their coupling with circulation and surface energy fluxes
The climatological rainband position in the tropics determines how clouds shape the tropical responses to extratropical forcing
Based on theory and climate model experiments, previous studies suggested that most of the uncertainties in projected future changes in meridional energy transport and zonal mean surface temperature ...can be attributed to cloud feedback. To investigate how radiative and dynamical adjustments modify the influence of cloud-radiative changes on energy transport, this study applies a cloud-locking technique in a fully coupled climate model, CESM. Under global warming, the impacts of cloud-radiative changes on the meridional energy transport are asymmetric in the two hemispheres. In the Northern Hemisphere, the cloud-radiative changes have little impact on energy transport because 89% of the cloud-induced heating is balanced locally by increasing outgoing longwave radiation. In the Southern Hemisphere, on the other hand, cloud-induced dynamical changes in the atmosphere and the ocean cause enhanced poleward energy transport, accounting for most of the increase in energy transport under warming. Our experiments highlight that the local longwave radiation adjustment induced by temperature variation can partially offset the impacts of cloud-radiative changes on energy transport, making the estimated impacts smaller than those obtained from directly integrating cloud-radiative changes in previous studies. It is also demonstrated that the cloud-radiative impacts on temperature and energy transport can be significantly modulated by the oceanic circulation, suggesting the necessity of considering atmospheric–oceanic coupling when estimating the impacts of cloud-radiative changes on the climate system.
The microwave dielectric properties and the microstructures of (Mg1−xCox)2TiO4 ceramics prepared by the conventional solid‐state route were investigated. Lattice parameters were also measured for ...specimens with different x. The formation of solid solution (Mg1−xCox)2TiO4 (x=0.02–0.1) was confirmed by the X‐ray diffraction patterns, energy dispersive X‐ray analysis, and the lattice parameters measured. By increasing x from 0 to 0.05, the Q×f of the specimen can be tremendously boosted from 150 000 GHz to a maximum of 286 000 GHz. A fine combination of microwave dielectric properties (ɛr∼15.7, Q×f∼286 000 GHz at 10.4 GHz, τf∼−52.5 ppm/°C) was achieved for (Mg0.95Co0.05)2TiO4 ceramics sintered at 1390°C for 4 h. Ilmenite‐structured (Mg0.95Co0.05)TiO3 was detected as a second phase. The presence of the second phase would cause no significant variation in the dielectric properties of the specimen because it possesses compatible properties compared with that of the main phase. In addition, only a small deviation in the dielectric properties was monitored for specimens with x=0.04–0.05 at 1360°–1420°C. It not only provides a wide process window but also ensures an extremely reliable material proposed as a very promising dielectric for low‐loss microwave and millimeter wave applications.
Composite ceramics in a solid solution of (Mg1−x Mnx)2TiO4 (x=0.02–0.1) have been prepared by the mixed oxide route. Formation of the solid solution was confirmed by the X‐ray diffraction, the EDX ...analysis, and the measured lattice parameters, which varied linearly from Mg2TiO4 (a=b=c=8.4410 Å) to (Mg0.9 Mn0.1)2TiO4 (a=b=c=8.4445 Å). The XRD analysis also confirmed the co‐existence of a cubic‐structured (Mg1−xMnx)2TiO4 and an ilmenite‐structured second phase (Mg1−xMnx)TiO3. The composition expected to have a maximum Q×f (276 200 GHz at 10.5 GHz) is (Mg0.95Mn0.05)2TiO4 with ɛr∼15.69 and τf∼−52.6 ppm/°C. The existence of the second phase, however, would lead to no significant variation in the dielectric properties of the specimen because it possesses compatible properties compared with that of the main phase.
With the goal of understanding the relative roles of anthropogenic and natural factors in driving observed cloud trends, this study investigates cloud changes associated with decadal variability ...including the Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation (AMO). In the preindustrial simulations of CMIP5 global climate models (GCMs), the spatial patterns and the vertical structures of the PDO-related cloud cover changes in the Pacific are consistent among models. Meanwhile, the models show consistent AMO impacts on high cloud cover in the tropical Atlantic, subtropical eastern Pacific, and equatorial central Pacific, and on low cloud cover in the North Atlantic and subtropical northeast Pacific. The cloud cover changes associated with the PDO and the AMO can be understood via the relationships between large-scale meteorological parameters and clouds on interannual time scales. When compared to the satellite records during the period of 1983–2009, the patterns of total and low cloud cover trends associated with decadal variability are significantly correlated with patterns of cloud cover trends in ISCCP observations. On the other hand, the pattern of the estimated greenhouse gas (GHG)-forced trends of total cloud cover differs from that related to decadal variability, and may explain the positive trends in the subtropical southeast Pacific, negative trends in the midlatitudes, and positive trends poleward of 50°N/S. In most models, the magnitude of the estimated decadal variability contribution to the observed cloud cover trends is larger than that contributed by GHG, suggesting the observed cloud cover trends are more closely related to decadal variability than to GHG-induced warming.
High‐dielectric constant and low‐loss ceramics in the (Zn1−xCox)Ta2O6 ceramics have been prepared by the conventional mixed oxide route and their microwave dielectric properties have been ...investigated. A phase change or crossover from ZnTa2O6 to CoTa2O6 occurred at x=0.07 and was completed at x=0.11 and it tends to form a continuous solid solution elsewhere. An over‐sintered specimen would lead to a slight decrease in the density resulting in a decline of the dielectric constant and the Q×f value. The specimen with x=0.05 possessed an excellent combination of microwave dielectric properties: ɛr∼38.47, Q×f∼112 000 GHz, and τf∼11.2 ppm/°C. It is proposed as a candidate material for today's 3G passive components and especially small‐sized GPS patch antennas.
Low‐loss ceramics having the chemical formula Mg2(Ti1−xSnx)O4 for x ranging from 0.01 to 0.09 have been prepared by the conventional mixed oxide route and their microwave dielectric properties have ...been investigated. X‐ray powder diffraction patterns indicate the corundum‐structured solid solutions for the prepared compounds. In addition, lattice parameters, which linearly increase from 8.4414 to 8.4441 Å with the rise of x from 0.01 to 0.09, also confirm the forming of solid solutions. By increasing x from 0.01 to 0.05, the Q×f of the specimen can be tremendously boosted from 173 000 GHz to a maximum 318 000 GHz. A fine combination of microwave dielectric properties (ɛr∼15.57, Q×f∼318 000 GHz at 10.8 GHz, τf∼−45.1 ppm/°C) was achieved for Mg2(Ti0.95Sn0.05)O4 ceramics sintered at 1390°C for 4 h. Ilmenite‐structured Mg(Ti0.95Sn0.05)O3 (ɛr∼16.67, Q×f∼275 000 GHz at 10.3 GHz, τf∼−53.2 ppm/°C) was detected as a second phase. The presence of the second phase, however, would cause no significant variation in the dielectric properties of the specimen, because the second phase properties are very similar to the primary phase. These unique properties, in particular, low ɛr and high Q×f, can be utilized as a very promising dielectric material for ultra‐high‐frequency applications.
The microwave dielectric properties and the microstructures of the (1-x)MgTiO3-x(Ca0.8Sr0.2)TiO3 ceramic system prepared by the conventional solid-state route were investigated. (Ca0.8Sr0.2)TiO3 was ...employed as a Ie" f compensator and was added to MgTiO3 to achieve a temperature-stable material. Ilmenite-structured MgTiO3 and perovskite-structured (Ca0.8Sr0.2)TiO3 were coexisted and the two-phase system was confirmed by the X-ray diffraction patterns and the energy-dispersive X-ray analysis. Although the I mu r of the specimen could be boosted by increasing amount of (Ca0.8Sr0.2)TiO3, it would instead render a decrease in the QA-f. The Ie" f value is strongly correlated to the compositions and can be controlled through the existing phases. In fact, Ie" f could be adjusted to a near-zero value by mixing 94mole% MgTiO3 and 6mole% (Ca0.8Sr0.2)TiO3. A dielectric constant (I mu r ) of 21.42, a high QA-f value of 83,700GHz (at 9GHz) and a temperature coefficient of resonant frequency (Ie" f ) of a degree 1.8ppm/A degree C were obtained for 0.94MgTiO3-0.06(Ca0.8Sr0.2)TiO3 sintered at 1300A degree C for 4h. It is proposed as a low-loss and low-cost dielectric material for microwave and millimeter wave applications.
The (Mg0.95M0.05)Ta2O6 (M=Ni, Zn, Mn) ceramics are prepared through the solid-state ceramic route and their microwave dielectric properties are investigated as a function of ionic radius difference ...of M and Mg. The forming of (Mg0.95M0.05)Ta2O6 solid solutions were confirmed by the XRD analysis and the measured lattice parameters and the ceramics showed a nonlinear variation of dielectric properties with the sintering temperature. In addition, the sintering temperature has slight effect on dielectric constant and temperature coefficient of resonant frequency, but significant on Q×f value. In particularly, (Mg0.95Ni0.05)Ta2O6 shows a relatively high Q×f of 88,300 GHz along with a dielectric constant of 28.73 and a τf of 44.9 ppm/°C, indicating the dielectric can be used for high-frequency applications.
► (Mg0.95M0.05)Ta2O6 solid solutions were synthesized by solid-state method. ► Measured lattice parameters were obtained. ► Compound using (Mg0.95Ni0.05)Ta2O6 shows a tremendous increase in the Q×f value.
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