The low latitude ionosphere and its coupling to lower atmosphere such as (mesosphere,rnstratosphere and thermosphere)and high latitude ionosphere are investigated usingrnobservational and model data. The dominant modes of variability of low latitudernionosphere are linked to Equatorial Electrojet (EEJ), Counter Electrojet(CEJ) andrnPrereversal Enhancement(PRE). These are investigated using magnetometer data andrnEEJ models. The results of the analysis reveal that EEJ undergoes day and seasonalrnvariations. From the daily variation analysis, the EEJ value at Addis Ababa sharplyrnincreases to its peak value from 9.00-13.00 LT and dies out around 18.00 LT. EEJrnversus time graphs shows that the H-components of the magnetic eld at Addis Ababarnlocation varies by a factor of 2-4 times larger compared to Adigrat. Seasonally asrnboth measurements and model data revealed, EEJ has signi cantly increased duringrnE season compared to D and J seasons. Our observation also shows that counter CEJrnare more frequent on solstices than equinoxes and on the contrary Morning CounterrnElectrojets (MCEJ) occurs more frequently on equinoxes than solstices. Apart fromrnthat the localized EEJ, CEJ and PRE, low latitude ionosphere is dynamically coupledrnto lower atmosphere and high latitude ionosphere that control both low latitudernionospheric dynamics and chemistry during both quiet and storm-time. In this regard,rnthe storm-time low latitude ionospheric total electron content (TEC) variability andrnthe inrnuences of lower and high latitude ionsophere are investigated.rnThe TEC variation is characterized in relation to diurnal, seasonal, temporal, spatialrnand longitudinal behaviors. The diurnal characteristics of TEC can be explainedrnin terms of the Diurnal, Semidiurnal,Terdiurnal and Quterdiurnal tides. The TECrnviirnviiirnclimatology from NeQuick and ionosonde is also compared during both quiet and geomagneticallyrndisturbed days. Day time enhanced TEC value followed by night timerndepilation is a typical behavior of the ionosphere.rnA geomagnetic storm occurred during January 22-25, 2012. The Disturbancernstorm time (Dst) values for the period shows that it is a moderate intensity geomagneticrnstorm. The geomagnetic storm is characterized by di erent indices andrnindicators. The Symmetric H component of ring current (SYMÃƒÂ€Â€Â€H) value on Januaryrn22 shows a sudden increase to more than 50 nT at the Sudden Storm Commencementrn(SSC) and followed by sharp decrease to a value of -100 nT after which arnrecovering started. A second SSC on January 24 followed by a shock on Januaryrn25. These SSCs before the main storms on January 22 and 25 are evidences for thernoccurrence of Coronal Mass Ejection (CME). Moreover, the short recovery period,rnunlike that of Co-rotating Interaction Regions (CIR) driven geomagnetic storms, impliesrnthe geomagnetic storm is a CME-driven. The sudden jump of the solar windrndynamic pressure and the The southward Interplanetary Magnetic Field (IMF Bz)rnare also consistent with occurrence of CME. Our observational evidences of Protonrnrnuxes of high energy ranges and increase in proton density are also other indicatorsrnfor occurrence of CME. The high values Auroral Electrojet (AE) index on theserndates implies ionospheric perturbation in response to the storm. This is also rernectedrnin the Total Electron Content (TEC) change during the storm relative to quiet dayrnTEC over the polar regions. The response of the ionospheric to geomagnetic stormsrnis also investigated from amplitude modulation of wave components that account forrnthe majority of TEC variance during the period. The diurnal and semidiurnal TECrnvariances account upto a maximum of 83% and 30% of the TEC variance over fairlyrnexclusive ionospheric regions respectively. The diurnal variability dominates the subtropicalrnlatitude where the solar cycle is an important factor while the semidiurnalrnvariance is limited to higher latitudes. The diurnal and semidiurnal TEC variancesrnshow hemispheric asymmetries. The stationary planetary waves also account for TECrnvariances that exceed semidiurnal TEC variance and exhibit hemispheric asymmetryrnixrnof opposite sign to diurnal TEC variance. These features of TEC variance are climatologyrnof TEC variability irrespective of the storms. However, the impact of therngeomagnetic storms are distinctly marked in the daily time series of amplitudes ofrndiurnal and semidiurnal migrating tides and stationary planetary waves. The abruptrnchanges in amplitudes of diurnal (upto 5 TECU) and semidiurnal (upto 2 TECU)rnmigrating tides are observed within the 20oS-20oN latitude band and along 20oN respectivelyrnwhile that of stationary planetary wavenumber 1 is in the order of 3 TECUrnand is mainly localized along 20oS