Journals
2018 EN
Jia Mingjiao · Xue Xianghui · Gu Shengyang
+5 more
Multiyear high‐frequency gravity wave (GW) momentum fluxes and variances in the mesosphere and lower thermosphere region are revealed using four meteor radars along 120°E longitude at Northern Hemisphere midlatitudes for the first time, which are located at Mohe (53.5°N, 122.3°E), Beijing (40.3°N, 116.2°E), Mengcheng (33.3°N, 116.5°E), and Wuhan (30.5°N, 114.2°E), respectively. The seasonal and latitudinal variations of GW momentum fluxes in the midlatitude are discussed. The directions of the monthly mean zonal momentum fluxes are mostly against the background mean zonal winds, which agree well with the selective filtering mechanism. The seasonal variations of meridional momentum fluxes have similar trends over all four stations. The latitudinal variations in the seasonal variation of GW momentum fluxes are mainly due to the latitudinal variations of background winds and GW sources. The unexpected eastward momentum fluxes in winter over Beijing are likely caused by the secondary GWs propagating eastward from the source region over the Tibetan Plateau (25°–40°N, 70–100°E). The GW variances show a V‐shaped structure indicating annual and semiannual variations over four stations in zonal component. A quasi‐4‐month oscillation was observed over Mohe, Mengcheng, and Wuhan in meridional component. The background winds play decisive roles in these GW variance structures.
Journals
2018 EN
Gu ShengYang · Ruan Haibing · Yang ChengYun
+3 more
Combined Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics (TIMED)/TIMED Doppler interferometer horizontal winds, Global Positioning System Total Electron Content maps, and Constellation Observing System for Meteorology, Ionosphere, and Climate electron density profiles are utilized to study the westward zonal wavenumber 1 quasi‐6‐day planetary wave in both the neutral atmosphere and F region ionosphere under solar minimum conditions in 2009. It is found that the zonal (meridional) wind perturbations maximize (minimize) in the geographic equatorial mesosphere and lower thermosphere region and are in phase (out of phase) between hemispheres, which agrees well with both the Upper Atmosphere Research Satellite/high‐resolution Doppler imager wind observations and (1, 1) Rossby normal mode. Analysis of the Total Electron Content maps and Constellation Observing System for Meteorology, Ionosphere, and Climate electron density profiles shows that the F region ionosphere exhibits wave spectra and temporal variations that are consistent with those of the neutral atmosphere. Specifically, the 6‐day oscillation in electron density is the highest during 1200–1800 LT in the equatorial ionospheric anomaly region (~20° geomagnetic latitude), with a minimum amplitude at the equator, which agrees well with the F region fountain effect. At 300 km, the amplitude of the electron density oscillation reaches ~1.2 × 10 4 cm −3 , which accounts for ~14% of the background value. In addition, the F 2 layer electron peak density and peak height also exhibit corresponding oscillations with amplitudes of ~9 × 10 4 cm −3 and ~12 km, respectively. The current work provides clear evidence for F region ionospheric responses to planetary waves in the mesosphere and lower thermosphere region.
Journals
2018 EN
Zou Zicheng · Xue Xianghui · Shen Chenglong
+4 more
A lot of solar proton events (SPEs) have happened during the ongoing solar cycle 24 including extremely large events. Seven large SPEs from 2012 to 2017 were chosen to find the response of polar atmosphere to them. Three SPEs happened in 2012, and the other four SPEs happened in 2013, 2014, 2015, and 2017, respectively. The National Oceanic and Atmospheric Administration Geostationary Operational Environmental Satellites 13 proton observations were used to illustrate the proton flux toward the Earth during each SPE. These energetic protons are deposited in the middle and upper atmosphere and ionize the neutral atmosphere constituents and create radicals HO x (H, OH, and HO 2 ). Enhancements in the upper atmospheric hydroperoxyl radical (HO 2 ) of both polar regions of over 1 ppbv are found in the Aura Microwave Limb Sounder measurements immediately after some SPEs happened. The Microwave Limb Sounder observations of ozone (O 3 ) show decreases of >10% in both polar middle and upper atmosphere for a few days with a peak value of >20–60% over 1–3 days. The compositions of HO 2 and ozone for all the selected SPEs indicate that the polar ozone depletions during the SPEs in a way are the result of the HO 2 enhancements.
Journals
2018 EN
Dang Tong · Lei Jiuhou · Wang Wenbin
+7 more
Abstract It is commonly believed that solar eclipses have a great impact on the ionosphere‐thermosphere (I‐T) system within the eclipse shadow, but little attention has been paid to the global response to these events. In this study, we investigate the global upper atmospheric responses to the recent Great American Solar Eclipse that occurred on 21 August 2017 using a high‐resolution coupled ionosphere‐thermosphere‐electrodynamics model. The simulation results show that the ionosphere and thermosphere response to the eclipse is not just local but global. Large‐scale traveling atmospheric disturbances (TADs), seen in the thermospheric temperature and winds, were triggered from the eclipse region and propagated in a southeast direction when the eclipse ended. A large total electron content (TEC) enhancement occurred over South America after the eclipse was over. The TEC enhancement was primarily the result of transport by the thermospheric wind perturbations associated with the eclipse‐induced TADs. The perturbations of TEC, neutral temperature, and winds exhibited asymmetric distributions with respect to the totality path during the solar eclipse. Furthermore, ionospheric electrodynamic processes also play an important role in the global responses of the I‐T system to the solar eclipse. Unlike the case of large‐scale TADs propagating from the eclipse region to other locations in the globe, the ionospheric electric fields and plasma drifts began to show significant perturbations even during the local pre‐eclipse period when local wind and temperature had not been perturbed. This is related to the instantaneous global response of the ionospheric current system to changes in the ionospheric conductivity and winds in the eclipse region.
Journals
2018 EN
Gu ShengYang · Dou Xiankang · Pancheva Dora
+2 more
A quasi 2‐day wave (QTDW) during the austral summer period usually coincides with a sudden stratospheric warming (SSW) event in the winter hemisphere, while the SSW influences on QTDWs are not totally understood. In this work, the hourly Navy Operational Global Atmospheric Prediction System‐Advanced Level Physics High Altitude reanalysis data sets during January/February 2006 are utilized to study the contribution of a major SSW on the anomalous QTDW activities during the same period. Our new findings are generalized as follows: (1) The summer easterly is enhanced during a SSW event due to the interhemispheric coupling, which is clearly indicated by the anomalous cross‐equator circulation from the winter to summer mesosphere. (2) The enhanced summer easterly could sustain critical layers for QTDWs with larger phase speeds (e.g., smaller zonal wave number or shortwave period) and strengthen the summer easterly barotropic/baroclinic instabilities, which are essential for the QTDW amplification through wave‐mean flow interactions. This is why a strong westward QTDW with zonal wave number 2 is identified besides the conventionally dominant wave mode of wave number 3, and their periods are only ~42–45 hr during January 2006. (3) The strong winter planetary waves during SSW periods facilitate the occurrence of the nonlinear interaction between QTDWs and stationary planetary waves, which is strongly suggested by the abnormal temporal variations of wave number 2 and wave number 3 QTDWs. We conclude that the anomalous QTDW behaviors in summer mesosphere during January 2006 are associated with the major SSW event in the winter stratosphere.
Journals
2018 EN
Ren Dexin · Lei Jiuhou · Wang Wenbin
+3 more
In this study, the in situ electron density measurements from the Challenging Minisatellite Payload (CHAMP) and solar extreme ultraviolet (EUV) radiation from the Solar Extreme Ultraviolet Experiment instrument on board the Thermosphere Ionosphere Mesosphere Energetic and Dynamics satellite, both with a time resolution of 1.5 hr, are used to explore the peak response of the ionospheric F 2 region plasma to the peak of 27‐day solar EUV flux variation. The time delays of in situ electron density changes obtained from the CHAMP satellite in response to 27‐day solar EUV flux changes vary from 0 to about 3 days. Meanwhile, the Thermosphere Ionosphere Electrodynamics General Circulation Model simulations driven by the measured EUV flux and the actual geomagnetic activity show similar time delays as those observed in the CHAMP measurements. Further simulations reveal that the geomagnetic activity greatly affects the determination of the ionospheric time delay to the 27‐day solar EUV flux variations. Besides, the solar zenith angle change within the solar rotation interval can cause large latitudinal differences in the time delay. The ionospheric time delay to the pure 27‐day solar EUV flux variation is less than 1 day and slightly increases with latitude, when geomagnetic activity and seasonal variations are eliminated in the simulation. The simulation results further suggest that the ionospheric response time is associated with the photochemical, dynamic, and electrodynamic processes in the ionosphere‐thermosphere system.
Journals
2018 EN
Wu J. F. · Xue X. H. · Liu H. L.
+2 more
National Center for Atmospheric Research Whole Atmosphere Community Climate Model (WACCM) with quasi‐uniform grid of ∼25‐km horizontal resolution can resolve gravity waves (GWs) with horizontal scales down to ∼250 km. In this study, the scale interactions between the GWs resolved by WACCM and those with smaller scales, its potential impact on the resolved waves, and the dependence of wave characteristics on spatial resolution are examined. The Weather Research and Forecasting (WRF) simulations with five different spatial resolutions (25, 20, 15, 10, and 4 km) are performed, with the high‐resolution WACCM wind and temperature fields as initial and boundary conditions. Semicircular GWs excited by a tropical cyclone (TC) resolved by WACCM and WRF (25‐km resolution) are found at similar locations and have similar structures. In this study, the sensitivity of GW structure to the choice of model horizontal resolutions is examined. Although WRF is successful in generating semicircular GWs in each case, the simulation reveals more power at shorter horizontal wavelengths of GWs at finer resolutions. Furthermore, we evaluate the performance of all these simulations in resolving GWs induced by the tropical cyclone (TGWs). The magnitude of the zonal momentum flux calculated from the high‐resolution WACCM is greater than the WRF‐25 simulation, in addition, the magnitude is comparable to the results from the WRF‐15 and WRF‐10 simulations.
Journals
2018 EN
Wang Lingmin · Luan Xiaoli · Lei Jiuhou
+1 more
The Lyman‐Birge‐Hopfield‐long band dayglow emissions near 1,700 Å, which were observed by the ultraviolet imager on board Polar satellite, are characterized as a cosine‐like function of the solar zenith angle. These emissions are mainly excited by the solar extreme ultraviolet produced photoelectrons acting on the nitrogen molecules. The amplitude and phase factors are used to quantify the cosine‐like function and subsequently develop a dayglow model. In this study, a model is developed by considering broader dayglow emission areas outside the auroral oval, as the dayglow intensities in the dayside can exceed the auroral brightness, especially in summer. Also, this model is constructed by considering the seasonal variations of the two factors. It is demonstrated that, besides the strong solar cycle and universal time dependencies, the amplitude factors of the cosine‐like function show prominent seasonal variations, which are associated with the solar zenith angle changes. The amplitude factors are the largest in summer and smallest in winter. In addition, the dayglow phase factors show nearly constant values within each season, but throughout the year, they are higher in summer and equinoctial months and lower in winter. The dayglow model can benefit the investigation of global auroral patterns for all seasons.
American Geophysical Union
Journals
2018 EN
Xiaobing Dou · Songtao Li · Linfeng Hu
+5 more
Oxidative stress and TNFα are critically involved in the initiation and progression of non-alcoholic fatty liver disease (NAFLD). In this study, we investigated the effects of dysregulated glutathione homeostasis, a principal feature of oxidative stress, on TNFα-induced hepatotoxicity and its mechanistic implications in NAFLD progression. We showed that mice fed a high-fat diet (HFD) for 12 weeks developed hepatic steatosis and liver injuries, which were associated with not only TNFα overproduction but also hepatic glutathione dysregulation, characterized by GSH reduction and GSSG elevation. Moreover, consuming a HFD increased protein S-glutathionylation (protein-SSG formation) in the liver. Subsequent cell culture studies revealed that GSSG accumulation, as opposed to GSH reduction, sensitized hepatocytes to TNFα killing by reducing the TNFα-triggered NF-κB activity. GSSG prevented TNFα-induced activation of IKK-β, an upstream kinase in the NF-κB signaling pathway, by inducing IKK-β glutathionylation (IKK-β-SSG formation). In animal studies, in comparison to a control diet, HFD consumption resulted in increased hepatic IKK-β-SSG formation, leading to suppressed IKK-β activation and subsequent NF-κB suppression. Furthermore, we found that HFD consumption also led to decreased hepatic expression of glutaredoxin, a key enzyme for de-glutathionylation. Similarly, CdCl 2 , a chemical inhibitor of glutaredoxin, sensitized hepatocytes to TNFα-mediated cytotoxicity. In conclusion, our data suggest that GSSG is a potent and clinically relevant sensitizer for TNFα-induced hepatotoxicity in NAFLD, which represents a potential therapeutic target for NAFLD.
Journals
2018 EN
Yuning Liao · Xiaohong Xia · Ningning Liu
+8 more
It has been well known that androgen receptor (AR) is critical to prostate cancer development and progression. It has also been documented that AR is expressed in more than 60% of breast tumors, which promotes the growth of estrogen receptor-negative (ER - )/AR-positive (AR + ) breast cancer cells. Thus, AR might be a potential therapeutic target for AR-positive/ER-negative breast cancer patients. Previously we reported that in prostate cancer cells proteasome-associated deubiquitinase ubiquitin-specific protease 14 (USP14) stabilized AR protein level by removing its ubiquitin chain. In the current study, we studied the USP14-AR protein interaction and cell proliferation status after USP14 reduction or inhibition in breast cancer cells, and our results support the conclusion that targeting USP14 is a novel strategy for treating AR-responsive breast cancer. We found that inhibition of USP14 accelerated the K48-ubiquitination and proteasome-mediated degradation of AR protein. Additionally, both genetic and pharmacological inhibition of USP14 significantly suppressed cell proliferation in AR-responsive breast cancer cells by blocking G 0 /G 1 o S phase transition and inducing apoptosis. Moreover, AR overexpression inhibited USP14 inhibition-induced events, suggesting that AR deubiquitination by USP14 is critical for breast cancer growth and USP14 inhibition is a possible strategy to treat AR-positive breast cancer.