查看更多>>摘要：Precipitation in the Arctic is expected to increase with implications to ecosystems and changes to atmospheric circulation. In the Arctic strong southerly wind, often known as atmospheric rivers, supply enormous moisture and heat into the Arctic and is expected to increase in future warming scenarios. The impact of these events on Arctic climate change is not yet understood fully. In this study precipitation associated with such an event is studied for Ny Alesund, Svalbard for 2016 March. During the event, the high precipitation was noticed between 22 and 23 UTC and 6-9 UTC on 12th March and 13th March respectively. It has been shown that during these two time periods, downwelling longwave radiation increased due to clouds. The enhanced downwelling longwave radiation increased the surface temperature locally. Above the shallow planetary boundary, advection dominated the temperature changes and initiated a shallow convection in the atmosphere leading to intensified precipitation in the lower layers during the event. Enhanced vertical velocity in MRR could be a result of this convection. Thus, the largescale southerly winds, that developed into an atmospheric river has not only contributed to the supply of heat and moisture but also enhanced cloud radiative effects and resulted in local warming. The moisture sources for this event appears to be Norwegian Sea and the east coast of Greenland. The scenario we have investigated was characterised by a warm Arctic with southerly warm winds. Studies suggest that convective scale precipitation is increasing in Eurasia under warm conditions. Our study points to the change in precipitation regime that Arctic may characterise as the warming continues.
查看更多>>摘要：Short- and long-term variabilities of stationary planetary waves (SPW) in the middle atmosphere are investigated from temperatures obtained from two satellites (Formosa Satellite-3/Constellation Observing System for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED)) and a reanalysis dataset (ERA-Interim). COSMIC data analysis with a smaller window size enables investigation of short-term variabilities and wavelet analysis shows the presence of 30 to 120 days oscillations in the stratosphere during different years and are attributed to wave-mean flow interactions. This result in observational data is seen only due to the use of COSMIC data and its unique sampling pattern that enabled the extraction of short-term variability. Additionally, annual and quasi-biennial features are also observed. SABER analysis also shows similar long-term variations. The annual variation in both datasets shows linearly increasing spectral power indicating that the stratosphere is increasingly becoming chaotic and irregular and the dynamics are becoming stronger and expanding equatorward. Vertically upward propagation of SPW1 and SPW2 into the mesosphere is hindered during Sudden Stratospheric Warmings (SSW) due to the prevalent westward winds and smaller mesospheric amplitudes are observed. During no SSW years, larger SPW1 and SPW2 amplitudes are seen in the mesosphere. A positive correlation is observed between COSMIC SPW amplitudes and gravity wave (GW) potential energy (E-p) while the longitudes of maximum amplitudes are out of phase.
de Assis Honorato Muella, Marcio TadeuMacho, Eduardo PerezCorreia, EmiliaSpogli, Luca...
12页
查看更多>>摘要：Scintillations are caused by ionospheric irregularities and can affect the propagation of trans-ionospheric radio signals. One way to understand and predict the impact of such irregularities on Global Navigation Satellite System (GNSS) signals is through the spatial/temporal characterization of the scintillation's climatology during different phases of a solar cycle covering different latitudes and longitudes. This characterization is performed using amplitude scintillation index S-4, during the full solar cycle 24, in the South American (SA) sector. The investigation considers the diurnal, daily, and seasonal variation of S-4 index for climatological purpose, and the goal of this study is to investigate the scintillations covering a large spatial scale during the full solar cycle 24. The characterization shows a latitudinal asymmetry, whereas at the south, the scintillations were more frequent and their peak was more distant from the magnetic equator, which can be attributed by the South Atlantic Magnetic Anomaly (SAMA), and/or by the transequatorial meridional neutral winds. It also shows a longitudinal asymmetry, where the scintillations at the eastern sector occurred between November and February, while at the western sector, they occurred during the months of October, November, February and March, which can be attributed to the difference between the magnetic and geographic equators. The occurrence of scintillations during two distinct geomagnetic storms with similar storm time in the SA sector is also presented.
NSTL
Elsevier