almost from the time of their discovery , the radiation belts have been understood to be composed of two distinct zones of trapped energetic particles separated by a lower intensity slot region [ van allen , 1959 ; van allen and frank , 1959 ] .
those early studies referred to all trapped energetic electrons as  radiation belt electrons . 
for example , characterized the energy and pitch angle distributions of radiation belt electrons in the inner and outer zones over energies from 50 to 4000  kev .
they described the structure of the radiation belts this way :  the inner edge of the inner zone is certainly determined by the upper atmosphere of the earth , and the outer part of the outer zone is determined by the magnetopause .
the distribution of particle intensities between these places seems to show a persistent vacancy called the slot .
 the inner magnetosphere contains a multitude of plasma and energetic particle populations each with different ( but intertwined ) dynamics .
these populations include the plasmasphere , the plasma sheet , substorm injection regions , electron and ion ring current , and the proton radiation belt in addition to the inner and outer zone radiation belt populations .
synonymously which raises the question of whether tens and hundreds of kev electrons are accurately described as radiation belt electrons or whether focusing on mev radiation belt electrons is too limited .
figure  1 shows a schematic of radiation belt processes that illustrates some of the populations and processes that are important for radiation belt dynamics .
mediumenergy ( i.e. , tens to hundreds kev ) electrons and ions from the plasma sheet and substorm injections e    b and gradientcurvature drift sunward and eastward or westward around the earth . if the distribution functions are unstable to the growth of waves , these electrons can become a  source population  providing the energy for waves that resonate with radiation belt electrons .
a particularly important process is the local acceleration of mev electrons in the outer zone consistent with acceleration by vlf whistler mode chorus waves [ summers et al . , 1998 ;
; chen et al . , 2007 ; reeves et al . , 2013 ; thorne et al . , 2013 ; reeves , 2015 , and references therein ] .
electrons with energies of hundreds of kev are often referred to as the  seed population  [ obara et al .
preexisting mev electrons are also further accelerated to even higher energies . a schematic illustration of radiation belt structures and processes [ from reeves et al . ,
the plasmasphere is a highdensity region that , typically , shows a steep density gradient at the plasmapause .
it fills a region where corotational e    b drift dominates over sunward e    b drift  a region that can vary greatly with the strength of the convection electric field .
first , the dramatic difference in densities inside and outside the plasmasphere affects both wave growth and radiation belt resonance conditions .
second , in steady state , the plasmapause defines a boundary that plasma sheet and substorminjected electrons can not penetrate . in reality
though , the different timedependent drifts of plasmasphere and plasma sheet / injection electrons can cause the populations to overlap in spatially and temporally localized regions .
third , the persistent presence of vlf whistler mode hiss inside the plasmasphere tends to scatter radiation belt electrons into the atmospheric loss cone which is thought to be the primary mechanism responsible for the formation of the radiation belt slot region [ lyons and thorne , 1973 ] .
analyzed monthly averages of > 2  mev electron fluxes from sampex ( the solar anomalous and magnetospheric particle explorer ) and found that over many years , the inner edge of the outer radiation belt tracked the average location of the plasmapause quite closely while goldstein et al .  
most of the attention on the radiation belts in recent decades has focused on the dynamics of >  1  mev electrons in the outer belt .
the excellent , longterm data sets from goes and sampex have been extensively studied and have focused particular attention on > 2  mev electrons . in contrast , the dynamics of tens to hundreds of kev electrons in the slot and inner zone have not been as extensively studied as the greater than mev electrons .
protons in the proton belt with energies greater than tens of mev can not be shielded out , and many intended electron measurements can be shown to be dominated by penetrating protons .
mev electrons can produce high backgrounds in two ways : by direct penetration above the instrument shielding threshold and by bremsstrahlung xray production in the instrument .
the van allen probes satellites [ mauk et al . , 2012 ] were designed to overcome those limitations and are able to provide high temporal resolution measurements of electrons from ev to mev . in this paper
we present initial observations of kev to mev electron dynamics in the slot and inner zone and consider potential implications for current theories of radiation belt and inner magnetospheric processes .
we discuss radiation belt dynamics as a function of l shell for different energies . in section 4
section 6 discusses how the radiation belt fluxes are enhanced and how some energies are transported or injected earthward into and through the slot region .
section 7 discusses energy and l shelldependent loss rates and how the belts decay back toward a quiescent state .
( we frequently refer to the two satellites by their prelaunch designations radiation belt storm probe ( rbsp)a and rbspb . )
the satellites are in a nearequatorial orbit with apogee   5.8  re and an orbital period of   9  h and a spin period of   11  s. the van allen probes satellites carry an extensive suite of particle and fields measurements . in this study we present observations from two of the three particle instruments in the rbspenergetic particle , composition , and thermal plasma ( ect ) suite [ spence et al . ,
2013 ] , the helium oxygen proton electron ( hope ) plasma spectrometer [ funsten et al . , 2013 ] , and the magnetic electron ion spectrometer ( mageis ) [ blake et al . ,
hope measures electrons and ions ( with composition ) from 1  ev ( or spacecraft potential ) to 50  kev in 5 look directions and 72 energy steps with energy resolution e / e    15% .
it uses a spherical electrostatic analyzer followed by time of flight ( tof ) chambers and channel electron multipliers .
in addition , careful accounting start , stop , and tof signals actively reject backgrounds from radiation that does penetrate the shielding [ funsten et al .
mageis measures electrons from 20  kev to 4.8  mev using four magnetic spectrometers covering three overlapping energy ranges and ions from 55  kev to ~20  mev using a range telescope .
the magnetic spectrometers focus electrons within a selected energy pass band upon a focal plane of several silicon detectors where pulseheight analysis is used to determine if the energy of the incident electron is equivalent to the electron momentum selected by the magnet .
thus , each event is a twoparameter analysis , an approach leading to a greatly reduced background .
the solidstate detectors measure the full spectrum both inside and outside the energy passband selected by the spectrometer .
since the energy selection is strictly controlled by the magnetic spectrometer , signals outside the primary detector passband are all background [ blake et al . , 2013 ] .
groundbased processing software can then determine the signaltonoise ratio in each energy bin and actively subtract any backgrounds that contribute to the signal within the primary passband [ claudepierre et al .
in addition to their design features , both instruments are heavily shielded making the hope and mageis measurements the best to date for unambiguously measuring the dynamics of kev to mev electrons in the slot and inner zone .
( the third ect instrument , the relativistic electron proton spectrometer [ baker et al . , 2012 ] , provides similar measurements at higher energies than are used in the current study . ) in this analysis , for both instruments , we use release three of the spinaveraged , 11  s data available at http://www.rbspect.lanl.gov .
figure  2 shows electron flux as a function of l shell and time for the year 2013 .
figures  2a2e show five energies , 1553  kev , 459  kev , 234  kev , 110  kev , and 46  kev , respectively . to ease comparison ,
all fluxes are plotted on scales covering 3 orders of magnitude but with different absolute ranges .
figures  2f2h show solar wind speed , the interplanetary magnetic field ( imf ) bz , and the dst index from omniweb ( http://omniweb.gsfc.nasa.gov ) . a multienergy view of flux as a function of l shell and time from the van allen probes mission for 2013 .
( a  d ) backgroundcorrected mageis electron fluxes , ( e ) electron fluxes from hope , and ( f  h ) geomagnetic indices : solar wind speed , imf bz , and dst .
dramatic differences in radiation belt electron behavior are seen at different energies and from event to event .
the 1553  kev electron panel ( figure  2a ) shows relativistic electron dynamics that are familiar from observations by missions such as crres [ vampola et al . ,
1992 ] , polar [ blake et al . , 1995 ] , and sampex [ baker et al . , 1993 ] .
the dynamics of the outer zone are dominated by episodic events that enhance or deplete fluxes in response to geomagnetic activity : storms , southward imf , and high solar wind speed [ reeves et al . ,
these observations are some of the first , however , that are essentially free of background contamination from bremsstrahlung xrays and penetrating particles [ claudepierre et al . ,
et al .   have shown , the main feature that differs from the expected behavior is that there are essentially no > 1  mev electrons in the inner zone at levels above background .
we know that the inner zone occasionally gets replenished during high geomagnetic activity when mev electrons penetrate through the slot region , deep into the inner magnetosphere as was observed in the halloween 2003 event [ baker et al . ,
2004 ] . however , during 2013 no such events were observed and the inner edge of the outer zone mev electrons never penetrated deeper than l    3 [ baker et al . ,
kev ( figure  2b ) the radiation belts have the expected twozone structure with a very dynamic outer zone , a fairly stable inner zone , and a slot region .
figures  2c2e show electrons with energies of 234 , 110 , and 46  kev , i.e. , energies that are usually associated with  seed  or  source  populations . yet even at these relatively low energies radiation beltlike features still exist .
specifically , there is a highly dynamic outer zone region with episodic enhancements of electron fluxes , a much less dynamic inner zone that is replenished during some of the outer zone enhancement events , and a slotlike region where quiet time fluxes are orders of magnitude lower than in the inner or outer zones .
this suggests that electrons with energies as low as tens of kev can indeed be considered radiation belt electrons and are likely affected by at least some of the same processes that control radiation belt dynamics at mev energies . in figure  3
we compare the number of flux enhancement events as a function of energy and l shell for the first half of 2013 . as also seen in figure  2 , at any given l shell
for example , at l 3.5 there were 22 events observed at 46  kev and only 4 events at 1.5  mev .
we note that the events at higher energies are always a subset of the lower energy events ; i.e. , there were no events identified at higher energies that were not also present at lower energies .
figure  3 also shows that at any given energy , there are fewer events that penetrate to low l shells . at 459  kev
of those 13 ( 87% ) penetrated to l  =  4.5 and 9 ( 60% ) penetrated to 3.5 but only 4 ( 3% ) penetrated to 2.5 .
the number of radiation belt enhancement events in the first 6  months of 2013 as a function of energy at l shells ranging from 2.5 to 5.5 .
we identify enhancement events visually when line plots of fluxes at fixed l shell show rapid increase , slower decay , and exceed a fixed flux threshold . at all l shells
there are more events at lower energy than at higher energy . at a given energy
most events that penetrate to l  =  5.5 also penetrate to l  =  4.5 , but few of them penetrate to l  =  2.5 .
to further investigate the energy dependence of penetration into and through the slot region , we return to figure  2 . at 1.5 
mev none of the events in 2013 extended below about l  =  3 , and no enhancement events were observed at l  =  2.5 . at 459  kev at least seven events in 2013 show flux enhancements that inject particles that penetrate through the slot region and at 234  kev there were at least 24 . summarizing these observations : 
 outer zone enhancements : at lower energies there tend to be more electron enhancements than at higher energies . or , said another way , a given event is more likely to produce an enhancement of lower energy electrons than it is to produce an enhancement at the higher energies .
notice , for example , the quiet period in september when 234  kev electrons show three clear enhancements , but 1553  kev electrons show only one.slot : in any given enhancement event lower energy electrons are more likely to fill the slot region and penetrate into the inner zone .
similarly , even when they do not fill the slot , lower energy electrons penetrate to lower l shells than higherenergy electrons.inner zone : enhancements of electrons in the inner zone are more common at lower energies , but interestingly , not every slot filling event produces longlasting enhancements of inner zone fluxes .
in addition , even in quiet times , the inner zone extends to higher l shells for lower energies , and consequently , the slot region is also found at higher l shells . 
 
outer zone enhancements : at lower energies there tend to be more electron enhancements than at higher energies . or
, said another way , a given event is more likely to produce an enhancement of lower energy electrons than it is to produce an enhancement at the higher energies .
notice , for example , the quiet period in september when 234  kev electrons show three clear enhancements , but 1553  kev electrons show only one .
slot : in any given enhancement event lower energy electrons are more likely to fill the slot region and penetrate into the inner zone . similarly , even when they do not fill the slot , lower energy electrons penetrate to lower l shells than higherenergy electrons .
inner zone : enhancements of electrons in the inner zone are more common at lower energies , but interestingly , not every slot filling event produces longlasting enhancements of inner zone fluxes . in addition , even in quiet times , the inner zone extends to higher l shells for lower energies , and consequently , the slot region is also found at higher l shells .
finally , we note that essentially , every feature of the radiation belts is energy dependent and exhibit a striking coherence across a broad spectrum of energies .
we see energy dependence during flux enhancement events and in the relatively quiet times between enhancement events .
in this section we explore the energydependent structure of the radiation belts during relatively quiet times .
this provides a baseline against which to compare the episodic enhancement and transport of outer belt electrons into and through the slot region .
the features we will discuss are the typical features observed between enhancement events , but it is important to note that enhancement events come too frequently to call the quiescent conditions  equilibrium  states .
figure  4 provides a view on the energydependent structure of the radiation belts in a different format than is commonly used .
here we plot electron flux as a function of l shell over a very broad range of energies spanning 1  kev to 4  mev .
broadspectrum  format provides a complementary view to the more traditional plots of l shell and time at several fixed energies ( e.g. , figure  2 ) .
hope electron fluxes from 1 to 50  kev ( < 1  kev hope data are not considered in this study ) and backgroundcorrected mageis data from 50  kev to 4  mev plotted as a function of energy and l shell .
this shows on pass through the radiation belts during quiet times : the inbound leg of rbspa orbit 485 ( 11:14 to 15:43 ut on 27 february ) .
figure  4 plots hope data from 1 to 50  kev ( < 1  kev hope data are not considered in this study ) and backgroundcorrected mageis data from 50  kev to 4  mev .
the gaps in mageis coverage are energy channels where the current background correction algorithm has not been fully validated .
extending the observations down to 1  kev highlights the fact that the inner zone is actually the dominant structure of the radiation belts during quiet times .
one of the clearest features of the inner zone population is its energydependent outer edge .
as was shown in figure  2 the outer edge of the inner belt is observed at low l shells for high energies and at higher l shells for lower energies . at ~  800  kev
the inner zone extends out to only l    2 while at ~50  kev it extends to l    4 .
this format also shows more clearly that the l dependence is continuous over a wide range of energies ; from ~800  kev down to as low as ~10  kev .
the outer zone electrons in this period are also clearly visible but since this was chosen as a relatively quiet time , their fluxes are relatively low .
there is an interesting , and somewhat unexpected , energy dependence to the inner edge of the outer zone . at l 
  4.5 ( in this case ) there is a minimum in flux as a function of energy which appears in this format as a 
the result is an inner boundary to the outer belt that could be described as  s shaped .
 the combined energydependent structures of the inner zone and outer zone create an energydependent slot region . at energies where there is a clear minimum in the slot ( 10  kev to   1  mev for this time )
the slot is wider and deeper at high energies and is narrower and shallower at low energies . where fluxes are substantially above background
, the location of the slot minimum is found at higher l shells for lower energies .
returning to figure  2 , it is apparent that the detailed energydependent state of the radiation belts is a function of the preceding enhancement event and the amount of time since that event . in the following sections we show that the features seen in figure  4 are produced by a combination of acceleration , transport , and loss processes .
in this section we discuss the energy and timedependent structure of the radiation belts spanning an enhancement event that started on 1 march 2013 .
figure  5 shows the solar wind speed , imf bz , ae index , dst index , and rbspa orbit from 21 february to 13 march 2013 .
the event started late on 28 february with a modest interval of southward imf and increasing solar wind speed .
the nextday solar wind speeds peaked at nearly 650  km / s and dst dipped below 50  nt .
solar wind speed , imf bz , ae , dst , and the orbital l shell for rbspa are shown for the 1 march 2013 radiation belt enhancement event .
figure  6 shows how the energydependent structures in the radiation belts develop and evolve during the 1 march enhancement event .
each plot shows data from the inbound half of the orbit ( i.e. , apogee to perigee ) for rbspa .
each orbit is separated in time by ~9  h , and each inbound pass takes ~4.5 
h. colorcoded mageis backgroundcorrected electron fluxes plotted as a function of energy and l shell .
( left column ) ( orbits 487491 ) the enhancement and transport of electrons over ~2  days .
( right column ) selected orbits over the ~4  days following the event when electron fluxes were decaying . figure  6 ( left column ) shows the enhancement of fluxes and transport into and through the slot region .
the enhancement and transport occur over five orbits that span the ~2  day interval from 28 february at 09:41 ut before the solar wind driving intensified through the main phase of the storm , ending 2 march at 02:03 ut .
orbits 487 and 488 show the quiet time structure that was discussed in the previous section .
the first signs of the enhancement event in figure  6 appear on orbit 489 as substorminjected electrons began to penetrate to lower l shells .
( substorm injection activity is presented in figure  8 and will be discussed in more detail later . ) by orbit 490 the flux of outer zone electrons at all energies below 1  mev had been enhanced , and the inner boundary was shifted to lower l shells .
substantial fluxes of 200  kev electrons were observed below l    3.5 , while on the previous orbit they only appeared above l    4.0 . at energies close to 1  mev
the change is subtle , but there is still an inward motion of the boundary of l    0.1 .
we note , however , that on orbit 490 , rbspa had not yet seen any enhancement of >  1  mev electrons . on orbits 491 and 492 , as geosynchronous substorm injection activity continued and dst remained low , the trends in the radiation belt enhancement continued . by then fluxes of > 1  mev electrons in the outer zone
were enhanced above preevent levels , while fluxes of electrons with energies less than 1  mev continued to penetrate to lower l shells . for this event , substantial filling of the slot region
was observed at all energies up to ~300  kev but not much above that energy .
orbit 491 ended at 02:05 on 2 march by which time the enhanced structure of the radiation belts could be called  fully developed .
 the characteristics of the fully developed 1 march enhancement event include ( a ) enhanced fluxes in the outer belt at energies up to > 3  mev and ( b ) filling of the slot region at and enhanced fluxes of electrons in the inner zone at energies up to ~300  kev , but ( c ) no filling of the slot or change in the fluxes of inner zone electrons above ~300  kev .
we also note , in particular , a rather unexpected feature of the outer zone electrons .
the inner edge of the activetime outer belt is highly energy dependent and can be fit quite well with a straight line in log(energy ) versus l shell . to quantify the energy dependence of the boundary
, we used the steepest slope on the radial gradient to define the energy dependence more quantitatively .
for the 336  kev channel the steepest gradient is located between 3  <  l  <  4 with a midpoint of l    3.5 . in the 737  kev channel the steep gradient lies between 3.5  <  l  <  4.2 with a midpoint at l    3.8 and a midpoint of the 2.2  mev channel at l    4.5 . as is also suggested by the color contours in figure  6 , those points define a straight line in log(energy ) versus l , specifically l 
 min  =  0.3  +  1.2 log(e ) with e in kev .
figure  6 ( right column ) shows the evolution of the radiation belts over the next ~4  days .
the decay of electron fluxes in the slot region begins almost immediately and quickly returns the belts to a quiescent state quite similar to the state the existed prior to the enhancement event .
the intent of this paper is primarily to document , observationally , the energy and l shelldependent states of the radiation belts and the transitions from quiescent to enhanced and back to quiescent .
it is , however , natural to ask why the enhancement and transport of electrons to low l , into the slot , and/or into the inner zone are so energy dependent , why they vary from event to event , and what physical processes are responsible ? answering those questions will , no doubt , take further observational , theoretical , and modeling studies .
but , here we explore , briefly , the possible roles that storm time convection and substormlike injections might play .
figure  7 shows four electron energies as line plots that highlight the flux enhancements and earthward transport .
the lines are color coded by orbit running from orbit 487 in blue to orbit 491 in red .
the outbound and inbound legs are at different local times , so both spatial and temporal differences can be seen  particularly at low energies .
28 at 5:11 ut ( blue ) ; orbit 488 ( cyan ) ; orbit 489 ( green ) ; orbit 490 ( orange ) ; and orbit 491 , ending march 2 at 02:00 ut ( red ) .
each orbit takes ~9 hours . the inbound and outbound legs sample different local times .
substorm injections , filling of the slot region , and earthward penetration of the outer zone are all apparent .
for all four energies there is a distinct slot at the beginning of the interval on orbit 487 ( blue lines ) . by orbit 491 ( red lines , 36  h later )
the slot is completely filled at energies up to at least 146  kev and large increases of fluxes in the slot are observed up to at least 336  kev .
each orbit is only 9  h , and the entire interval plotted is only 45  h ( 28 february , 5:11 ut to 2 march , 2:00 ut ) .
figures  7 ( first panel ) and 7 ( second panel ) show quite dynamic variations from passtopass down to at least l 
presented a case study that clearly linked an injection seen at l    2.5 to substorm activity seen at geosynchronous orbit and beyond .
figure  8 presents substorm injection activity on 1 march 2015 from six los alamos national laboratory ( lanl)geo satellites along with data from van allen probes ( a and b ) .
it does not appear in figure  6 because rbspa was at perigee at the time .
injection frequency increased again starting around 08:00 ut and continued for the remainder of the day and into 2 march when dst began to recover ( figure  5 ) .
substorm injection activity on 1 march 2013 measured at geosynchronous orbit and by the two van allen probes satellites in elliptical orbits .
the lanlgeo synchronous orbit particle analyzers ( sopa ) electron data spans ~50 to ~500  kev and rbsp data spans ~40 to ~600  kev .
previous studies have shown that the  injection front  ( the earthward edge of the dispersionless injection region ) moves earthward inside geosynchronous orbit with a speed of tens of km / s [ reeves et al . , 1996 ;
malaspina et al . , 2014 ] at least to the vicinity of l    4.5 [ friedel et al . ,
1996 ] , but it is hard to imagine that the inductive fields that produce dispersionless substorm injections extend down to l    2.5 .
turner et al .   attributed the deep injection to a twostep process involving dispersionless substorm injections and further transport by a fast magnetosonic wave at pi2 frequencies .
a third mechanism that may play an important role is enhanced crosstail electric fields driven by dayside reconnection .
enhanced storm time convection increases the sunward directed convective flow and pushes the ( energydependent ) alfvn boundaries earthward on the nightside .
thaller et al .   analyzed the event on 1 june 2013 and found ~12  mv / m electric fields down to l shells as low as ~2.3 .
there is no question that this strong convective transport can , in principal , open up drift paths that bring ions and electrons deep into the inner magnetosphere .
the differences between electron and ion dynamics , however , suggest that enhanced storm time convection alone can not produce the observed slotfilling effects .
this can be seen by comparing the ion fluxes plotted in figure  9 with the electrons plotted in figures  2 and 6 . at 20  kev ,
electrons , protons , oxygen , and helium can all be injected to very low l. but , in 2013 , 140  kev protons are never injected below l    3 whereas electrons of the same energy routinely are .
for the 1 march event , 140  kev ions fluxes were only enhanced down to l    4 whereas 146  kev electrons fluxes were enhanced down to l    2.5 .
the competing effects of corotation and gradientcurvature drifts should , if anything , bring ions deeper into the magnetosphere than electrons .
ion fluxes as a function of l shell and time along with solar wind speed , bz , and dst plotted in the same format in figure  2 .
( c  e ) 20  kev protons , helium ions , and oxygen ions .
ions with 20 and 45  kev energies penetrate more deeply and decay more quickly than at 140  kev .
comparison with figures  2 and 7 shows that ~140  kev electrons fill the slot quite frequently in 2013 while 140  kev ions were not injected below l    3 .
we also considered if charge exchange losses could mask possible ion injection signatures at low l. if charge exchange were faster than transport , then ions might be lost before they could be injected whereas electrons would not be .
this does not seem to be the explanation though . since 20  kev protons are injected below l    3 , earthward transport of 20  kev protons
charge exchange is slower even slower for 140  kev protons than it is for 20  kev protons , so if earthward transport is faster than losses at 20  kev , then earthward transport is much faster than losses at 140  kev .
it is likely that 140  kev protons do not penetrate as deeply as 20  kev protons because gradientcurvature drifts become dominant .
however , gradientcurvature drifts also affect electrons , so the difference between ion and electron behavior must be attributed to some other transport or acceleration processes that act on electrons but not ions . local acceleration by waveparticle interactions is one such process .
the observations of the 1 march 2013 event does show characteristics that may be consistent with local acceleration  particularly at energies above those that penetrate the slot .
however , the energydependent earthward boundary of the outer zone is difficult to reconcile with local acceleration alone .
chorus should accelerate electrons over a wide range of energies wherever chorus is present . while it may be possible for chorus acceleration to produce an inner edge of the outer belt that is linear in log(energy ) versus l shell , it is not readily apparent how that would happen .
since no one mechanism seems able to account for the observations , it is probable that several different mechanisms are acting together .
direct substorm injections , enhanced earthward convection , local acceleration and some additional earthward transport process such as magnetosonic wave resonance may all act in combination to produce the energydependent earthward transport of radiation belt electrons , filling of the slot region , and injection into the inner zone .
we now consider the recovery of the 1 march 2013 event from enhanced to quiescent states and discuss the role of electron losses , pitch angle scattering , and plasmaspheric hiss .
figure  6 shows the evolution of the slot region over the ~4  days immediately following the enhancement .
the decay of electron fluxes in the region l    2.54 begins almost immediately .
it is apparent that the rate of decay depends both on l shell and on energy .
for example , at l  =  4.5 the fluxes of 70  kev electrons decrease more quickly than at 700  kev .
specifically , figure  10 shows the flux as a function of time for four energies and two l shells . at l 
=  5 , in the heart of the outer belt , lifetimes become longer and longer with increasing energy . in contrast , at l  =  4 the lifetimes at 146 and 336  kev are shorter than they are at higher ( 737  kev ) or at lower ( 57  kev ) energies .
it is these energy and l shelldependent loss rates that create the biteout and sshaped outer belt boundary that was discussed previously .
flux as a function of time for four different electron energies ( 57737  kev ) at l  =  5 and l  =  4 .
all curves show the exponential decay expected for losses from pitch angle scattering by whistler mode waves . at l 
=  5 lifetimes are shorter for lower energies and longer for higher energies , but at l  =  4 the lifetime of 146 and 336  kev electrons are shorter than at higher ( 737  kev ) or lower ( 57  kev ) energies .
the minimum lifetimes at a few 100  kev at l  =  4 are consistent with expectations from hiss and are what produce the bite out of fluxes in that range of energyl space as seen in , e.g. , figure  4 .
similar energy and l dependencies to the loss rates create the inner zone . for example , at l  =  3 the fluxes of 200  kev electrons decrease more quickly than the fluxes of 50  kev electrons leaving a sharp boundary to the inner zone that can be described approximately by l 
 max  =  72 log(e ) with e in kev .
the different loss rates as a function of energy and l shell discussed here are based only on observations and do not depend on any particular physical mechanism .
we note , however , that losses at these energies and l shells have often been attributed to pitch angle scattering from whistler mode hiss [ lyons et al . , 1972 ; lyons and thorne , 1973 ; santolk et al . , 2001 ; meredith et al . , 2006 , 2007 ; summers et al . , 2007 ;
meredith et al .   calculated electron lifetimes for plasmaspheric hiss as a function of energy and l and found that at l  =  4 the minimum lifetime occurred for ~200  kev consistent with our results .
they also found that at lower l shells , the lifetimes for a given energy got progressively longer which likely explains the energy dependence of the inner zone population .
( highly resolved effects of whistlermode hiss waves in march 2013 , journal of geophysical research , manuscript in preparation , 2015 ) used van allen probes plasma and wave observations for the same 1 march 2013 event to calculate electron lifetimes as a function of energy and l shell and found good agreement with the observed lifetimes presented here .
we have presented an analysis of the dynamics of the radiation belts from the van allen probes mission .
newly available data that have had penetrating background removed enables studies in the slot and inner zone that were previously ambiguous or difficult to interpret .
the highenergyresolution measurements from hope and mageis show that radiation belt dynamics are coherent across a broad range of energies down as low as a few tens of kev .
even tens and hundreds of kev electrons show a spatial structure with an inner zone , slot , and outer zone commonly thought to be typical of the radiation belts , but above 1  mev the  typical  inner zone is absent throughout 2013 .
we investigated the energydependent dynamics of radiation belt enhancements at multiple energies ( figures  2 and 3 ) .
we found that ( 1 ) at any given l shell there are more enhancement events at lower energy than there are at higher energies ; ( 2 ) enhancement events therefore appear to have an upper energy limit that varies from event to event ; ( 3 ) at any given energy the number of events observed decreases with l but some events penetrate more deeply than others ; ( 4 ) therefore , in any given event lower energy electrons are more likely to fill the slot region and penetrate into the inner zone ; ( 5 ) electrons that do penetrate through the slot have an upper energy  threshold ,  but the maximum energy varies from event to event ; and ( 6 ) enhancements in the inner zone are also more common at lower energies , but not every slotfilling event produces longlasting enhancements of inner zone fluxes .
broadspectrum plots of flux as a function of energy and l shell show additional energydependent features that are not as readily apparent in multienergy plots of flux as a function of l shell and time .
figure  11 summarizes our results for quiet and active conditions . during quiet conditions the inner zone has an outer boundary
versus l and the outer zone has an inner boundary that is s shaped with a bite out of fluxes at a few 100  kev . during active conditions electrons
are injected into ( and/or accelerated within ) the slot region and fill the slot up to some maximum energy threshold . above that threshold lower energies penetrate still penetrate to lower forming an energydependent inner boundary to the active outer belt that is also often remarkably linear in log(energy ) versus l thus forming a pair of boundaries shaped something like a  v. 
subsequent energydependent losses remove the electrons that were injected into the slot and reform a linear inner zone boundary and an sshaped outer zone boundary .
flux as a function of energy and l shell for quiet ( inbound orbit 484 ) and active ( inbound orbit 492 ) conditions . under quiet conditions
the inner zone has a triangular shape with an outer boundary that is nearly linear in log(energy ) versus l. during 2013 the inner zone population only extended up to energies   1  mev .
the energyl structure implies that over some range , higher energy electrons have higher fluxes than lower energy electrons as seen in the line plot . in quiet times
there is a flux minimum in the slot region down to energies of tens of kev . in active conditions outer zone electron fluxes
are enhanced producing an inner boundary that is closer to the earth at lower energies than at higher energies .
fluxes in the slot region are enhanced over a broad range of energies , and up to some threshold energy , the slot is completely filled in . at energies above that threshold the inner zone fluxes are replenished , while above that threshold the inner zone fluxes are unaffected .
figure  12 presents this broadspectrum view for six additional events from march to june 2013 as marked in figure  12a . in figures  12b12 m
figures  12b , 12d , 12f , 12h , 12j , and 12l show the quiescent state before the storm , and figures  12c , 12e , 12 g , 12i , 12k , and 12 m show the active conditions near the peak of the storm . while there are important and interesting differences , all six events show striking similarities to the 1 march event .
in particular , in active conditions ( figures  12c , 12e , 12 g , 12i , 12k , and 12 m ) all events show an inner boundary for the outer belt that is strongly energy dependent . in order to better see the penetration and filling of the slot region ,
we have drawn a straight line approximating the energy dependence of the enhanced outer zone fluxes and reproduced same lines on the plots of the quiescent states before the events .
interestingly , for the 24 april and 1 may events , the preexisting population of highenergy electrons at low l shells ( i.e. , to the left of the dashed line ) is relatively unaffected by the enhancement event .
( a ) 459  kev flux as a function of l and time along with the dst index .
( b  m ) flux as a function of energy and l shell for individual orbits prior to an enhancement event ( figures  12b , 12d , 12f , 12h , 12j , and 12l ) and during the active part of the event ( figures  12c , 12e , 12 g , 12i , 12k , and 12 m ) . figures  12b12 m use arbitrary color scales that keep the dynamic range approximately the same for each event .
the orbits plotted are figure  12b : 529 ; figure  12c : 535 ; figure  12d : 633 ; figure  12e : 637 ; figure  12f : 651 ; figure  12 g : 655 ; figure  12h : 713 ; figure  12i : 718 ; figure  12j : 732 ; figure  12k : 737 ; figure  12l : 748 ; and figure  12 m : 753 . the quiescent conditions before these events show more variation than the active conditions do . as can be seen from figure  12a , this is at least in part a function of the intensity of the previous enhancement and the length of time between events when the electron fluxes are decaying .
for example , prior to the 17 march and 24 april events the slot was much broader in l and extended to lower energies than the 1 and 7 june events . at times the upper and lower portions of the sshaped boundary are highly asymmetric but retain the characteristic bite out that defines the lower portion of the s. it is also interesting to consider sequential events .
figure  12j shows the quiet state of the radiation belts before the event on 1 june , but it is also the quiet state resulting from the decay of the event on 25 may ( figure  12i ) .
the broadspectrum plots in figures  11 and 12 all show qualitatively similar energy dependencies and behaviors both in active conditions when fluxes are accelerated and injected and in the quiet conditions when fluxes are decaying .
the strong coherence across a broad range of energies and the qualitative similarities among events need to be better understood .
they must also provide clues about the underlying processes that may be common to all radiation belt enhancement events but that are obscured by the strong differences among events when viewed at fixed energies or spatial locations .
 abstractwe present observations of the radiation belts from the helium oxygen proton electron and magnetic electron ion spectrometer particle detectors on the van allen probes satellites that illustrate the energy dependence and l shell dependence of radiation belt enhancements and decays . 
 we survey events in 2013 and analyze an event on 1 march in more detail . 
 the observations show the following : ( a ) at all l shells , lower energy electrons are enhanced more often than higher energies ; ( b ) events that fill the slot region are more common at lower energies ; ( c ) enhancements of electrons in the inner zone are more common at lower energies ; and ( d ) even when events do not fully fill the slot region , enhancements at lower energies tend to extend to lower l shells than higher energies . during enhancement events the outer zone extends to lower l shells at lower energies while being confined to higher l shells at higher energies . 
 the inner zone shows the opposite with an outer boundary at higher l shells for lower energies . 
 both boundaries are nearly straight in log(energy ) versus l shell space . at energies below a few 100  kev , radiation belt electron penetration through the slot region into the inner zone is commonplace , but the number and frequency of  slot filling  
 events decreases with increasing energy . 
 the inner zone is enhanced only at energies that penetrate through the slot . 
 energy and l shelldependent losses ( that are consistent with whistler hiss interactions ) return the belts to more quiescent conditions . 
Introduction
Van Allen Probes Data
EnergyDependent Dynamics
Quiet Time Structure
The 1 March 2013 Enhancement Event
Radiation Belt Enhancement and Transport Through the Slot
Recovery From Enhanced to Quiescent States (Losses)
Conclusions