ALBERT

Description: Waves with frequencies in the vicinity of the oxygen cyclotron frequency and its harmonics have been regularly observed on the Van Allen Probes satellites during geomagnetic storms. We focus on properties of these waves and present events from the main phase of two storms on November 1, 2012 and March 17, 2013 and associated dropouts of ~ few MeV electron fluxes. They are electromagnetic, in the frequency range ~0.5 – several Hz, and amplitude ~0.1- a few nT in magnetic and ~0.1- a few mV/m in electric field, with both the wave velocity and the Poynting vector directed almost parallel to the background magnetic field. These properties are very similar to those of electromagnetic ion cyclotron (EMIC) waves, which are believed to contribute to loss of ring current ions and radiation belt electrons and therefore can be also important for inner magnetosphere dynamics.

Description: Up to now our understanding of the 11-year ozone solar cycle signal (SCS) in the upper stratosphere has been largely based on the SAGE II (v6.2) data record which indicated a large positive signal which could not be reproduced by models, calling into question our understanding of the chemistry of the upper stratosphere. Here we present an analysis of new v7.0 SAGE II data which shows a smaller upper stratosphere ozone SCS, due to a more realistic ozone-temperature anti-correlation. New simulations from a state-of-art 3-D chemical transport model show a small SCS in the upper stratosphere which is in agreement with SAGE v7.0 data, and the shorter HALOE and MLS records. However, despite these improvements in the SAGE II data, there are still large in current observational and meteorological reanalysis datasets, so accurate quantification of the influence of solar flux variability on the climate system remains an open scientific question.

Description: Aerosols and their effect on the radiative properties of clouds are one of the largest sources of uncertainty in calculations of the Earth's energy budget. Here the sensitivity of aerosol cloud-albedo effect forcing to 31 aerosol parameters is quantified. Sensitivities are compared over three periods; 1850-2008, 1978-2008 and 1998-2008. Despite declining global anthropogenic SO2 emissions during 1978-2008, a cancellation of regional positive and negative forcings leads to a near-zero global mean cloud-albedo effect forcing. In contrast to existing negative estimates, our results suggest that the aerosol cloud-albedo effect was likely positive (0.006 to 0.028 Wm -2 ) in the recent decade, making it harder to explain the temperature hiatus as a forced response. Proportional contributions to forcing variance from aerosol processes and natural and anthropogenic emissions are found to be period dependent. To better constrain forcing estimates, the processes that dominate uncertainty on the timescale of interest must be better understood.

Description: We have extensively evaluated the response of cloud-base drizzle rate ( R cb ; mm day –1 ) in warm clouds to liquid water path (LWP; g m –2 ) and to cloud condensation nuclei (CCN) number concentration ( N CCN ; cm –3 ), an aerosol proxy. This evaluation is based on a 19-month long dataset of Doppler radar, lidar, microwave radiometers and aerosol observing systems from the Atmospheric Radiation Measurement (ARM) Mobile Facility deployments at the Azores and in Germany. Assuming 0.55% supersaturation to calculate N CCN , we found a power law , indicating that R cb decreases by a factor of 2–3 as N CCN increases from 200 to 1000 cm –3 for fixed LWP. Additionally, the precipitation susceptibility to N CCN ranges between 0.5 and 0.9, in agreement with values from simulations and aircraft measurements. Surprisingly, the susceptibility of the probability of precipitation from our analysis is much higher than that from CloudSat estimates, but agrees well with simulations from a multi-scale high-resolution aerosol-climate model. Although scale issues are not completely resolved in the intercomparisons, our results are encouraging, suggesting that it is possible for multi-scale models to accurately simulate the response of LWP to aerosol perturbations.

Description: Electromagnetic ion cyclotron (EMIC) waves are transverse plasma waves generated by anisotropic proton distributions with Tperp 〉 Tpara. They are believed to play an important role in the dynamics of the ring current and potentially, of the radiation belts. Therefore it is important to know their localization in the magnetosphere and the magnetospheric and solar wind conditions which lead to their generation. Our earlier observations from three Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes demonstrated that strong magnetospheric compressions associated with high solar wind dynamic pressure (Pdyn) may drive EMIC waves in the inner dayside magnetosphere, just inside the plasmapause. Previously, magnetospheric compressions were found to generate EMIC waves mainly close to the magnetopause. In this work we use an automated detection algorithm of EMIC Pc1 waves observed by THEMIS between May 2007 to December 2011 and present the occurrence rate of those waves as a function of L-shell, magnetic local time (MLT), Pdyn, AE, and SYMH. Consistent with earlier studies we find that the dayside (sunward of the terminator) outer magnetosphere is a preferential location for EMIC activity, with the occurrence rate in this region being strongly controlled by solar wind dynamic pressure. High EMIC occurrence, preferentially at 12–15 MLT, is also associated with high AE. Our analysis of 26 magnetic storms with Dst  〈 −50 nT showed that the storm-time EMIC occurrence rate in the inner magnetosphere remains low (

Description: [1]  Recently, electromagnetic ion cyclotron (EMIC) wave generation in plasmaspheric plumes has been the subject of extensive discussion. Theory predicts that regions of detached cold, dense plasma immersed in relatively low background magnetic field should aid EMIC wave growth and may provide conditions for interaction between the EMIC waves and relativistic (MeV) electrons leading to energetic particle loss into the atmosphere. Since plasmaspheric plumes are specific to disturbed geomagnetic conditions, the link between EMIC waves and plumes may be especially important for radiation belt dynamics during magnetic storms. In this work, we present an in-situ survey of EMIC waves in plasmaspheric plumes using data from the Cluster satellites and will address the question of whether plumes are important for EMIC wave generation from a statistical perspective. We used a survey of plasmaspheric plumes between 2001–2006 identified from the WHISPER sounder measurements. We further identified EMIC waves from simultaneous (with WHISPER) magnetic field measurements by the FGM instruments and investigated the relationship between these two data sets. Only 10% of the time when Cluster observed plumes along its orbit did we also observe EMIC waves. The wave occurrence outside plumes is further significantly reduced and is ~20 times lower in immediately adjacent regions than inside plumes. We found that cold plasma density was not a good predictor of EMIC occurrence inside the plumes and that the absolute density does not affect the EMIC probability. On the other hand, enhanced solar wind dynamic pressure significantly increases EMIC wave occurrence rate inside the plumes.

Description: [1]   Abstract : We report on internal , magnetospheric processes related to markedly different storm-time responses of phase space density ( PSD ) in invariant coordinates corresponding to equatorially mirroring , relativistic electrons in Earth ’ s outer radiation belt . Two storms are studied in detail , selected from a database of 53 events ( Dst min  〈 - 40 nT ) during the THEMIS era thus far ( Dec . 2007 - Aug . 2012 ). These storms are well-covered by a number of in situ THEMIS spacecraft and complemented by additional ground-based and in situ observatories , and they epitomize the divergent behaviors that the outer radiation belt electrons can exhibit during active periods , even during otherwise similar Dst and auroral electrojet ( AE ) profiles . From our statistical results with the full database , the changes in the radial profile peak in PSD reveal notably consistent behavior with prior studies : 58 % of geomagnetic storms resulted in PSD peak enhancements , 17 % resulted in PSD peak depletions , and 25 % resulted in no significant change in the PSD peak after the storm . For the two case studies , we examined the PSD at multiple equatorial locations ( using THEMIS ), trapped and precipitating fluxes from low-Earth orbit ( using POES ), and chorus , hiss , EMIC , and ULF waves ( using THEMIS spacecraft , ground observatories , and the GOES spacecraft ). We show that : 1 ) peaks in PSD were collocated with observed chorus waves outside of the plasmapause during the most active periods of the PSD-enhancing storm , but not during the PSD-depleting storm , providing evidence for the importance of local acceleration by wave-particle interactions with chorus ; 2 ) outer belt dropouts occurred following solar wind pressure enhancements during both storms and were consistent with losses from magnetopause shadowing and subsequent outward radial transport ; during the PSD-enhancing storm , this revealed how the outer belt can replenish itself seemingly independently of the remnant of the pre-existing belt leftover after a dropout , which in this case resulted in a double-peaked outer belt distribution ; 3 ) slow decay in PSD was associated with corresponding locations in L * and enhanced wave amplitudes of plasmaspheric hiss ; 4 ) precipitation loss associated with wave-particle interactions with hiss and EMIC waves appeared to be significantly more important during the PSD-depleting storm than the PSD-enhancing storm ; and 5 ) PSD transport during the recovery phase of both storms and throughout the PSD-enhancing storm was consistent with ULF-wave driven radial diffusion away from maxima in PSD ; this indicates the importance of ULF waves in redistributing outer belt PSD after local acceleration occurs . We conclude that these source , transport , and loss processes , individually well characterized by previous studies , do indeed appear to act in concert , leading to predominance of local acceleration in one case and loss in another . These processes can therefore conspire towards optimal source or loss of outer belt electrons under suitable external drivers , and the conditions resulting in wave growth for these acceleration and loss mechanisms are therefore an important area of future research .

Description: Long-lasting (〉 20 h) EMIC Pc1-2 waves were observed by the Athabasca ( L = ∼4.6) induction magnetometer and CARISMA ( L = ∼4-6) fluxgate magnetometers on 5 April 2007. These waves showed a systematic frequency change with local time; the minimum frequency near dusk and the maximum frequency near dawn. Assuming the plasmapause as a potential source region of the waves, we estimated the plasmapause location from localized proton enhancement (LPE) events observed at NOAA-POES and METOP-2 satellites. We found that the longitudinal frequency variation of EMIC waves has a clear correlation with the estimated plasmapause location and that the waves are in the frequency band between the equatorial helium and oxygen gyrofrequencies at the estimated plasmapause. With our analysis results we suggest that the LPE events are caused by wave-particle interaction with the helium-band EMIC waves generated near the plasmapause.