Ionosphere Variability at Mid Latitudes during Sudden Stratosphere Warmings

Transcription

1 Ionosphere Variability at Mid Latitudes during Sudden Stratosphere Warmings Nick Pedatella 1 and Astrid Maute 2 1 COSMIC Program Office, University Corporation for Atmospheric Research 2 High Altitude Observatory, National Center for Atmospheric Research 3 rd International Conference on GPS Radio Occultation March 9, 2016

2 Sudden stratosphere warmings are dynamical disturbances in the high latitude wintertime stratosphere, mesosphere, and lower thermosphere. Characteristic features of SSWs: 1. Warming of the high latitude stratosphere 2. Cooling of the mesosphere 3. Warming of the lower thermosphere 4. Deceleration and/or reversal of stratospheric winds Zonal Mean Temperature, 70 N SSW ΔT (Day 0 Day 20)

3 Although the dynamical changes associated with SSW occur in the high latitude stratosphere and mesosphere, observations reveal large changes in the equatorial ionosphere occur during SSWs. Change in F-region Vertical Plasma Drift Velocity Jicamarca, Peru (75W, 12S) m/s Stratosphere Temp. The changes in equatorial plasma drifts will impact low latitude ionosphere electron densities (Chau et al., 2010)

4 Consistent changes occur in equatorial vertical drifts and low-latitude electron densities Change in F-region Vertical Plasma Drift Velocity Jicamarca, Peru (75W, 12S) SSW ΔTEC

5 In addition to the equatorial ionosphere variability, model simulations reveal large changes in the thermosphere winds during SSW Pre-SSW SSW Difference Pre-SSW SSW (Liu et al., 2014)

6 Due to their impact on the F-region peak height, the changes in thermosphere neutral winds are a potential source of mid-latitude ionosphere variability during SSWs U V U U V U Equatorward wind in Southern Hemisphere will increase hmf2 *opposite response in Northern Hemisphere Poleward wind in Southern Hemisphere will decrease hmf2 U: Neutral wind U : Field-aligned neutral wind V : Field-aligned plasma velocity Pre-SSW SSW Objective: Investigate mid-latitude hmf2 variability during SSWs, and its connection to variability in thermosphere neutral winds

7 Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) simulations of the 2009 SSW - TIME-GCM simulates from the stratosphere (10 hpa) to the upper thermosphere (4.6x10-10 hpa, ~ km), including a comprehensive ionosphere with self-consistent electrodynamics - To reproduce the middle atmosphere dynamics during the 2009 SSW, TIME-GCM is nudged towards WACCMX simulations, which are constrained by a reanalysis, up to ~95 km - Simulations are performed both with and without the migrating semidiurnal lunar tide (M2) - Simulations are performed with constant low solar and geomagnetic activity (F107 = 75 sfu) - Results are compared with COSMIC hmf2 observations Reference: Pedatella, N. M., H.-L. Liu, F. Sassi, J. Lei, J. L. Chau, and X. Zhang (2014), Ionosphere variability during the 2009 SSW: Influence of the lunar semidiurnal tide and mechanisms producing electron density variability, J. Geophys. Res., 119, , doi: /2014ja019849

8 The simulations are run with and without the lunar tide since this was previously demonstrated to improve the simulated variability in the equatorial region (Pedatella et al., 2014)

9 The TIME-GCM simulation with lunar tide forcing reproduces the observed short-term hmf2 variability COSMIC Obs. TIME-GCM without M2 TIME-GCM with M2 Results based on five day zonal mean

10 Perturbations in hmf2 reveal not only equatorial variability, but also variability at middle to high latitudes in the Southern Hemisphere. COSMIC Obs. TIME-GCM without M2 TIME-GCM with M2 Equatorial variability driven by ExB drifts Mid latitude variability driven by neutral winds?

11 The field aligned neutral wind (U ) exhibits significant variability at middle to high latitudes in the Southern Hemisphere TIME-GCM without M2 TIME-GCM with M2

12 The Southern Hemisphere hmf2 perturbations correspond to changes in U, indicating that changes in thermosphere neutral winds drive the mid latitude ionosphere variability. Results from simulation with lunar tide forcing

13 Why do perturbations occur primarily in the Southern Hemisphere? 360 km Global scale wave model (GSWM) simulations by Forbes and Zhang [2013] show largest increase in M2 occurs in the Southern Hemisphere thermosphere during the 2009 SSW. TIME-GCM simulations reveal most notable hmf2 perturbations with inclusion of the lunar tide We hypothesize that changes in the middle atmosphere during SSWs result in an enhanced M2 in the Southern Hemisphere thermosphere, leading to the ionosphere variability

14 Analysis of the TIME-GCM simulation results reveals large changes in the thermosphere M2 occur during the SSW time periods, and are largest in the Southern Hemisphere VN, M2 Amplitude DOY 010, 2009 VN, M2 Amplitude DOY 029, 2009 Pre-SSW SSW Difference DOY , 2009

15 Summary and Conclusions - COSMIC observations and TIME-GCM simulations both reveal large variability in the mid latitude ionosphere F-region peak height during SSWs - The hmf2 changes are indicative of the thermosphere neutral wind variability, and we find good agreement between the perturbations in hmf2 and the field aligned neutral wind Pre-SSW SSW - The mid latitude ionosphere-thermosphere variability is largest in the Southern Hemisphere - The thermosphere wind variability appears to be driven by the enhanced propagation of tides into the thermosphere during SSWs, especially the M2 lunar tide - Similar variations are seen during the 2013 SSW, suggesting that the middle latitude ionosphere-thermosphere variability is a consistent feature of SSWs

16 UCAR/COSMIC POSTDOCTORAL FELLOWSHIPS Support early career scientists with an interest in GNSS remote sensing Appointment Term: Up to two years Areas of Research Numerical Weather Prediction Climate Space Weather Weather and Water GNSS and RO retrieval development Emerging GNSS research opportunities, including GNSS reflectometry Location: Boulder, Colorado Apply by 15 April 2016 for maximum consideration Please see: For questions, please contact Dr. John Braun at