Incoherent Scatter Radar Study of the E region Ionosphere at Arecibo

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1 Incoherent Scatter Radar Study of the E region Ionosphere at Arecibo TheionosphericE regionliesinthealtituderangeof90to150km.thisregionsupportsawide rangeofwaves,includinggravitywaves,tides,andplanetarywaves.inthisregion,theionized andneutralparticlestransitfromcompletelycoupledinthelowere regiontoveryweakly coupledattheuppere region.thisistheregionwherethinionizationlayersareformeddueto themagneticfieldandtherapidaltitudinalvariationoftheneutralwind.fluiddynamics, electrodynamicsandtheircouplingarefullymanifestedinthisregion.thegreatsensitivityof theareciboincoherentscatterradar(isr)providesthemostaccuratemeasurementsof electronconcentration,iondrift,andionandelectrontemperatures,neutralwindsand electricalfieldwithveryhightimeandheightresolutions.theareciboisrhasplayedavitalrole instudyingtheenergetics,dynamics,couplingandcompositionsinthee region.withaslewof co locatedopticalandradiosensors,theareciboisrwillcontinueitspivotalroleinthestudyof theionosphereandtheatmosphere.thefollowingsummarizesafewtopicsthatcanbebest carriedoutatarecibo. Study of Gravity Waves, Tides and Planetary Waves Gravitywavescanhaveaperiodofasshortasafewminutes.ThefactthatAreciboISRcan measuretheelectronconcentrationwithatimeresolutionofafewsecondsmakesitthe primary,ifnottheonly,instrumenttostudye regiongravitywaves.figure1showselectron densityprofilesobtainedbydjuthetal.(1997)usingtheplasmalinetechnique.djuthetal. havefurtherstudiedtherelationshipoftheverticalwavelengthofthegravitywavesasa functionofaltitude,whichisshowninfigure2.thegeneraltrendisthatthevertical wavelengthincreaseswithaltitudes.subsequentstudiesrevealthatgravitywavesare ubiquitousatarecibo(djuthetal.2004). TheAreciboISRisanimportantground basedtoolinstudyingtides.thetidalwavescanbe seeninthewindobservationsaswellasintemperatureobservations,asillustratedinfigure3 (Zhouetal.1997).Itisgenerallyregardedthatdiurnalandsemidiurnaltides(withaperiodof 24and12hrrespectively)arethedominanttidalmodes.ArecentstudyatAreciboshowsthat terdiurnaltide(8hrperiod)cancompetewiththediurnalandsemidiurnaltides(gongand Zhou2011).Figure4showsthepowerspectralanalysisofthemeridionalwindmeasuredat Arecibo.Otherthantidalperiods,aplanetarywavewithaperiodof2 daycanalsobeseen. Further,spectralpeakat1.5/daymaybearesultofnon linearinteractionbetweenatwo day planetarywaveandthediurnaltide.figure5revealstheimpactofa2 dayplanetarywaveon electronconcentration.thepenetrationofelectronstoloweraltitudesonodddaysaround90 kmisduetoverticaltransportoflong livedions mostlikelymetallicions(zhou1998). ScientificquestionsthatcanbemosteffectivelypursuedbytheAreciboincoherentscatter radarinclude: Whatarethegenerationmechanismsandpropagationcharacteristicsofthegravity waves,tidesandplanetarywaves?

2 Howdogravitywaves,tides,planetarywavesandmeanflowinteractwitheachother? Howdothedifferentwavesandtheirinteractionsaffecttheenergetics,composition andtemperaturestructures? Study of Layered Phenomena Oneofthemostinterestingphenomenaintheionosphereistheformationofthinionization layers,oftencalledsporadice soreslayers.whilesporadice smayvaryinintensity,their occurrenceatareciboisquiteregular.itsgenerationiswellunderstoodtobeduetowinds pushingtheionsacrossthegeomagneticfieldlinesinoppositedirections.figure6showsion layersobservedatarecibo(mathewsetal.,1997).rapidmodulationoftheeslayershavebeen showntobeassociatedwiththequasi periodicechoesobservedbyvhfcoherentscatter radars(hyselletal.,2004).thesethinionizationlayershavealsobeenobservedtobe associatedwithneutralatomlayers,suchasna,fe,kandca(e.g.zhouetal.2008).thecolocatedresonancelidarsandopticalinstrumentsmakeareciboobservatoryaprimarysiteto studynotonlytheeslayersbutalsotheneutralmetalliclayersinthelowerpartofthee region, aswellastheirconnectionswithmeteoricinput. AnothertypeofthinionizationlayersfrequentlyobservedatAreciboistheso called intermediatelayers.thistypeoflayerisformedattheupperpartofthee regionandbecomes partoftheessystemoncedescendingintothelowerpartofthee region,asshowninfigure6. Onequestionregardingtheintermediatelayerisitscomposition.Eslayersaregenerally understoodtobecomposedofmetallicionsgeneratedthroughmeteoricablations. Intermediatelayers,asshownbyRoddyetal.(2004),maycontainalargefractionofmetallic ionsaswell.howdometallicionsgetuptothealtitudeswellabovemeteoricablationheightsis stillnotwellunderstood. Study of E region Electric Field Electricfieldintheionospherealongthegeomagneticfieldlineisgenerallyregardedtobe negligiblebecauseofthehighconductanceinthisdirection.asaresult,theelectricfield perpendiculartothefieldlineisheightinvariant.thispropertyisthoughttoapplytoboththe F andthee regionwhereelectrondensityishighenoughandion neutralcollisionislow enoughfortheionospheretobehighlyanisotropic.arecentstudybyzhouetal.(2011), however,showsstrongevidencethatthee regionelectricfieldisnotheightinvariant.figure6 showsthededucedelectricfieldatarecibo.aheightvariantelectricfieldchallengesour fundamentalunderstandingofthephysicsoccurringintheionosphere.areciboobservatory s location(dipangle~45 o )anditsaccurateandhighresolutionmeasurementsmakeitbest suitedforthistypesofstudies.

3 References: Djuth, F. T., M. P. Sulzer, J. H. Elder, V. B. Wickwar, High-resolution studies of atmosphere-ionosphere coupling at Arecibo Observatory, Puerto Rico, RADIO SCIENCE 32, pp.: , Djuth, F, T., Sulzer, M. P., S. A. Gonzales, Mathews, J. D., Elder, J. H, Walterscheid, R. L, A continuum of gravity waves in the Arecibo thermosphere? Geophysical Research Letters, Vol 31, DOI: /2003GL019376, Gong, Y., and Q. Zhou, Incoherent scatter radar study of the terdiurnal tide in the E- and F-region heights at Arecibo, 38, L15101, doi: /2011gl048318, Hysell, D., M. Larsen, and Q. Zhou, Common volume coherent and incoherent scatter radar observations of midlatitude sporadic E layer echoes and QP echoes, Annales Geophysicae, 22, , Mathews, J. D., M. P. Sulzer, and P. Perillat, Aspects of layer electrodynamics inferred from highresolution ISR observations of the km ionosphere, Geophysical Research Letters, VOL. 24, NO.11, PAGES , JUNE 1, Roddy, P. A., G. D. Earle, C. M. Swenson, C. G. Carlson, and T. W. Bullett, Relative concentrations of molecular and metallic ions in midlatitude intermediate and sporadic-e layers, Geophysical Research Letters, VOL. 31, L19807, doi: /2004gl020604, Zhou, Q., M. P. Sulzer, and C. A. Tepley, An analysis of tidal and planetary waves in the neutral winds and temperature observed at the E-region, J. Geophys. Res., 102, 11,491-11,505, Zhou, Q., Two-day oscillation of electron concentration in the lower ionosphere, J. Atmos. Solar-Terr. Phys., 60, , Zhou, Q., S. Raizada, C. Tepley, J. Plane, Seasonal and diurnal variation of electron and iron densities at the meteor heights above Arecibo, J. Atmo. Solar-Terr. Phys., 70, 49-60, Zhou, Q. H., Y. T. Morton, C. M. Huang, N. Aponte, M. Sulzer, and S. Gonzalez, Incoherent scatter radar observation of E-region vertical electric field at Arecibo, Geophys. Res. Lett., 38, L01101, doi: /2010gl045549, 2011.

4 Figure1.Residualelectrondensityprofilesexpressedasapercentageofthemeanprofile.Thedouble arrowindicatesthemagnitudeofa2%fluctuation.timeperiodsareinunitesofminutesandare referencedto13:51ltonjuly10,1992.(fromdjuthetal.1997) Figure2.Verticalhalfwavelengthasafunction ofaltitudeobservedabove Arecibo(Djuthetal., 1997).

5 Figure3.IontemperatureasafunctionoftimeandaltitudeaboveinJanuary1993.Theredline indicatesthegeneralphaseprogressionresultedfromtides.(fromzhouetal.,1997) k ( e d u t i t l A (a) Frequency (1/24hrs) Figure4.PowerspectralanalysisofmeridionalwindmeasureatAreciboduringJan.14 23,2010.Tidal andplanetarywaveperiodsdominatethespectra.(fromgongandzhou,2011) 0

6 Figure5.ElectronconcentrationatAreciboduringJan.21toJan.28,1993.Penetrationofelectronsto loweraltitudesonodddaysisaresultofa2 dayplanetarywave.(fromzhou,1998) Figure6.SporadicEandintermediatelayersobservedatArecibo.(FromMathewsetal.,1997)

7 Figure7.DerivedverticalelectricfieldatArecibo(Zhouetal.2011).Theheightvaryingelectricfieldis notwellunderstood.