skip to main content


Title: Duration of Individual Relativistic Electron Microbursts: A Probe Into Their Scattering Mechanism
Abstract

We used the Solar Anomalous and Magnetospheric Particle Explorer to identify and quantify the duration of relativistic,MeV, electron microbursts. A typical relativistic microburst has amillisecond (ms) duration, and the interquartile range of the duration distribution is 70–140 ms. We investigated trends in the microburst duration as a function of geomagnetic activity, L‐shell, and magnetic local time (MLT). The clearest trend is in MLT: the median microburst duration doubles from 75 milliseconds at midnight to 140 milliseconds noon MLT. This trend is similar to the whistler mode chorus rising tone element duration trend, suggesting a possible relationship.

 
more » « less
NSF-PAR ID:
10374970
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
DOI PREFIX: 10.1029
Date Published:
Journal Name:
Geophysical Research Letters
Volume:
48
Issue:
17
ISSN:
0094-8276
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    The apparent end of the internally generated Martian magnetic field at 3.6–4.1 Ga is a key event in Martian history and has been linked to insufficient core cooling. We investigate the thermal and magnetic evolution of the Martian core and mantle using parameterized models and considered three improvements on previous studies. First, our models account for thermal stratification in the core. Second, the models are constrained by estimates for the present‐day areotherm. Third, we consider core thermal conductivity,, values in the range 5–40 Was suggested by recent experiments on iron alloys at Mars core conditions. The majority of our models indicate that the core of Mars is fully conductive at present with core temperatures greater than 1940 K. All of our models are consistent with the range ofW. Models with an activation volume of 6 (0)require a mantle reference viscosity of Pa s.

     
    more » « less
  2. Abstract

    As the abyssal oceans warm, stratification is also expected to change in response. This change may impact mixing and vertical transport by altering the buoyancy flux, internal wave generation, and turbulent dissipation. In this study, repeated surveys of three hydrographic sections in the Southwest Pacific Basin between the 1990s and 2010s are used to estimate the change in buoyancy frequency. We find that below the°C isotherm,is on average reduced by a scaling factor of, a 12% reduction, per decade that intensifies with depth. At°C, we observe the biggest change:, or a 29% reduction per decade. Within the same period, the magnitude of vertical diffusive heat flux is also reduced by about, although this estimate is sensitive to the choice of estimated diffusivity. Finally, implications of these results for the heat budget and global ocean circulation are qualitatively discussed.

     
    more » « less
  3. Abstract

    We present the average distribution of energetic electrons in Jupiter's plasma sheet and outer radiation belt near the magnetic equator during Juno's first 29 orbits. Juno observed a clear decrease of magnetic field amplitude and enhancement of energetic electron fluxes over 0.1–1,000 keV energies when traveling through the plasma sheet. In the radiation belts, Juno observed pancake‐shaped electron distributions with high fluxes at ∼90° pitch angle and whistler‐mode waves. Our survey indicates that the statistical electron flux at each energy tends to increase fromto. The equatorial pitch angle distributions are isotropic or field‐aligned in the plasma sheet and gradually become pancake‐shaped at. The electron phase space density gradients atMeV/G are relatively small atand become positive over, suggesting the dominant role of adiabatic radial transport at highershells, and the possible loss processes at lowershells.

     
    more » « less
  4. Abstract

    Experimental evidence shows that temperature‐humidity () similarity in the atmospheric surface layer (ASL) is reduced as Bowen ratio () increases over land. However, underlying physical mechanisms remain not well understood. With large‐eddy simulations,dissimilarity is investigated in the steady‐state, convective boundary layer (CBL) over homogeneous landscape with varying. Asincreases from 0.4 to 2.0, the entrainment ratio forslightly decreases but that forqlargely increases. As a result, local production of humidity variance is substantially enhanced in the upper CBL and transported to the lower CBL by vigorous large eddies, contributing significantly to nonlocal fraction. However, the increased temperature variance in the ASL associated with strong heat flux is larger than that transported from the upper CBL. Such asymmetry in vertical diffusion induced by varying partitioning of surface fluxes strongly regulatesdissimilarity even under perfect conditions valid for Monin‐Obukhov similarity theory.

     
    more » « less
  5. Abstract

    The mechanisms underlying observed global patterns of partitioning precipitation () to evapotranspiration () and runoff () are controversially debated. We test the hypothesis that asynchrony between climatic water supply and demand is sufficient to explain spatio‐temporal variability of water availability. We developed a simple analytical model forthat is determined by four dimensionless characteristics of intra‐annual water supply and demand asynchrony. The analytical model, populated with gridded climate data, accurately predicted global runoff patterns within 2%–4% of independent estimates from global climate models, with spatial patterns closely correlated to observations (). The supply‐demand asynchrony hypothesis provides a physically based explanation for variability of water availability using easily measurable characteristics of climate. The model revealed widespread responsiveness of water budgets to changes in climate asynchrony in almost every global region. Furthermore, the analytical model using global averages independently reproduced the Budyko curve () providing theoretical foundation for this widely used empirical relationship.

     
    more » « less