No abstract

An integrated aerosol analytical system was deployed in Nanjing, a megacity in the Yangtze River Delta, to measure size‐resolved aerosol mixing states, effective densities, cloud condensation nucleus (CCN) activities, and chemical composition in August 2013. It was found that aerosols were predominantly internally mixed. The average effective densities were 1.38 ± 0.09, 1.48 ± 0.08, and 1.53 ± 0.07 g cm−3 for 50, 80, and 120 nm particles, respectively. Although black carbon (BC) represented only 0.3%, 1.6%, and 3.3% of the particle mass, on average, it was present in 7%, 38%, and 47% of the total particle number concentration at 50, 80, and 120 nm, respectively, indicating that BC particles may contribute significantly to the total atmospheric aerosol population. Externally mixed BC was only occasionally observed with an effective density of 0.67–0.97 g cm−3. Aerosols sampled generally exhibited a relatively high CCN activity and hygroscopicity (κ = 0.35 ± 0.13). Both newly formed particles and freshly emitted BC particles were observed to age rapidly from photochemical processes, with a significant enhancement in the particle CCN activity and an increase in the effective density. Aerosols influenced by four different air masses presented similar CCN activation, indicating that CCN activation would be primarily dependent on the particle size rather than the particle origin (and hence original composition). Our results suggest that under highly active photochemical conditions as encountered in this study, particles from both local sources and regional transport can be rapidly converted into efficient CCN by photochemical aging, thereby making important contributions to the atmospheric CCN budget and exerting profound implications on aerosol indirect climate forcing.

A global MHD model is used to study the energy transfer from solar wind to magnetosphere through magnetopause under radial interplanetary magnetic fields (IMFs). We use the streamline method to determine the smooth surface of the magnetopause by searching the inner boundary of the solar-wind streamline and discuss the roles of magnetic reconnection and viscous interaction under radial IMFs, which we compare with cases of north–south IMFs. We find that (1) the energy transfer across the magnetopause is asymmetric between the northern and southern hemispheres due to different reconnection locations, particularly for electromagnetic energy; (2) for sunward IMF, the most significant area of the net input of mechanical energy occurs on the day side and near-Earth magnetotail, and the electromagnetic energy input in the northern hemisphere is much larger than in the southern hemisphere on the night side; (3) the mechanical and electromagnetic energy-transfer distribution in the northern (southern) hemisphere for earthward IMF is the same as that in the southern (northern) hemisphere for sunward IMF; (4) the electromagnetic energy input for radial IMF is two times larger than for northward IMF, but three times smaller than for southward IMF, the viscous effect is smaller than for northward IMF but comparable to that for southward IMF, the rate of energy transfer is 2.22% for radial IMF, which is lower than 4.95% for southward IMF, but higher than 1.7% for northward IMF; and (5) the Akasofu-type energy-coupling formula, ϵ, is not suitable for the solar-wind events dominated by IMF B x .

The aortic and ductal arch geometry and flow lead to the alterations in flow profile, velocity, pressure, and WSS in the aortic isthmus in normal and CoA models, which are conductive of ductal issue migration into these areas. A 55% reduction in the dimension of aortic isthmus is associated with exponential change in velocity, pressure, and WSS, a probable threshold for hemodynamically significant CoA.

The frozen-in interplanetary magnetic field (IMF) in the solar wind is one of the most important parameters affecting the Earth’s space weather. In the early studies of the IMF’s influence on space weather, significant effects of the north–south component of the IMF B Z were emphasized, while the radial component of the IMF B X was largely ignored. However, the IMF near the Earth is not always dominated by the north–south component of the IMF B Z , and the radial component of the IMF B X also plays an important role. However, while the effects of the IMF B X (cone angle) on the magnetopause have been studied in recent years, there has been much less effort to quantify the B X (cone angle) effects on the bow shock. In this paper, using the bow shock crossing data from multiple satellites, we investigate the IMF cone angle effect on the dayside and nightside of the bow shock. Our results show that under the radial IMF condition, the dayside of the bow shock is located closer to the Earth than the average. At the same time, on the nightside, the bow shock is farther away from the Earth than the average. The mechanism explaining the bow shock location under the radial IMF is not completely understood. We believe that the magnetosonic Mach number and unusual conditions of the magnetosheath, especially for low dynamic pressure, play an important role. In the future, more work is needed to describe the reactions of the Earth’s magnetosphere to different IMF orientations, especially to the radial IMF.