Impact of COSMIC observations in a whole atmosphere-ionosphere data assimilation model

Transcription

1 Impact of COSMIC observations in a whole atmosphere-ionosphere data assimilation model Nick Pedatella 1,2, Hanli Liu 1, Jing Liu 1, Jeffrey Anderson 3, and Kevin Raeder 3 1 High Altitude Observatory, NCAR 2 COSMIC Program Office, UCAR 3 Computational Information Systems Laboratory, NCAR

2 Motivation: Events in the lower atmosphere, such as sudden stratospheric warmings, are a significant source of ionosphere variability. Change in F-region Vertical Plasma Drift Velocity Jicamarca, Peru (75W, 12S) m/s Temp. (90 N, 10hPa) SSW ΔTEC TECU

3 Motivation: Events in the lower atmosphere, such as sudden stratospheric warmings, are a significant source of ionosphere variability. Change in F-region Vertical Plasma Drift Velocity Jicamarca, Peru (75W, 12S) m/s Temp. (90 N, 10hPa) SSW ΔTEC TECU To accurately model, and potentially forecast, the middle-upper atmosphere variability it is necessary to include lower atmospheric effects and constrain the model meteorology

4 Motivation: Development of a whole atmosphere-ionosphere data assimilation model offers the opportunity for extended ionosphere prediction due to predictability of the lower atmosphere. (Pedatella et al., 2018)

5 WACCMX WACCM TIEGCM Whole Atmosphere Community Climate Model extended (WACCMX) - WACCMX is built on top of the Whole Atmosphere Community Climate Model (WACCM), which is the high-top atmosphere model component of the Community Earth System Model (CESM) - Finite volume dynamical core (1.9º x 2.5º resolution) - Extends from surface to 4.1x10-10 hpa (~ km) - Gravity waves parameterized for orographic and nonorographic sources. - Comprehensive interactive chemistry package (MOZART) - Solar variability (long term & impulsive) - Latest version includes self-consistent ionospherethermosphere with electrodynamics - WACCMX enables study of variability due to both the lower atmosphere and solar/geomagnetic activity. Liu et al. (2018), Development and Validation of the Whole Atmosphere Community Climate Model with Thermosphere and Ionosphere Extension (WACCM-X 2.0), JAMES, doi: /2017ms

6 WACCMX+DART - Data assimilation in WACCMX is implemented using the Data Assimilation Research Testbed (DART) ensemble Kalman filter - Framework for WACCMX+DART is identical to WACCM+DART (next slide) - Same observations are assimilated in the troposphere, stratosphere, and mesosphere. - Main change between WACCMX+DART and WACCM+DART is increased damping in WACCMX. This was necessary for model stability, and to ensure that mixing from small scale waves introduced by the data assimilation do not excessively reduce thermosphere O/N 2 and electron density. - Changes made for model stability do have a slight negative impact on performance of the data assimilation in the troposphere-stratosphere. - Initial development and results focused on the 2009 sudden stratospheric warming: Pedatella, N. M., et al. (2018), Analysis and Hindcast Experiments of the 2009 Sudden Stratospheric Warming in WACCMX+DART, J. Geophys. Res., 123, doi: /2017ja

7 WACCM+DART - WACCM+DART provides an atmospheric reanalysis from the surface to the lower thermosphere (~145 km). - Conventional Lower Atmosphere Observations: Aircraft temperature and wind Radiosonde temperature and wind Satellite drift winds COSMIC GPS refractivity - Sparse Middle/Upper Atmosphere Observations: TIMED/SABER Temperature ( hpa) Aura MLS Temperature ( hpa) 500 hpa Geopotential Height 0000 UT 15 Nov., 2008 NCEP Reanalysis WACCM+DART - Typically use a 40-member ensemble, which is a tradeoff between computational expense and having a sufficiently large ensemble to capture a variety of atmospheric states. - WACCM+DART is useful for correcting model biases, studying dynamical variability due to sudden stratosphere warmings, and short-term tidal variability Pedatella, N. M., K. Raeder, J. L. Anderson, and H.-L. Liu (2014), Ensemble data assimilation in the Whole Atmosphere Community Climate Model, J. Geophys. Res., 119, doi: /2014JD

8 WACCMX+DART Observing System Simulation Experiments (OSSE) - Observing System Simulation Experiments (OSSE) are performed in WACCMX+DART in order to assess the importance of lower-middle atmosphere and ionosphere observations - Nature run is specified dynamics WACCMX, with the model dynamics constrained up to ~50 km by the NASA MERRA reanalysis for Dec to Feb All cases are initialized on Dec. 15, 2008 and are performed using 40 ensemble members with a 6-hour data assimilation cycle. Case CTL LA LA+C none Observations Lower-middle atmosphere obs. (0-100 km) Lower-middle atmosphere and COSMIC electron density observations

9 Middle atmosphere variability is captured in the LA and LA+C experiments, but is different in the CTL experiment

10 Middle atmosphere variability is captured in the LA and LA+C experiments, but is different in the CTL experiment CTL LA TRUTH

11 Ionosphere total electron content

12 Ionosphere total electron content LA and LA+C experiments capture the variability, but are biased low with respect to the truth

13 Equatorial average TEC variability is generally well captured by the CTL experiment except during the SSW time period CTL LA LA+C TRUTH

14 Wave variability in the mesosphere is larger when assimilating lower atmosphere observations, increasing the mixing in the MLT. Global U, hpa LA LA+C CTL TRUTH

15 Impact of enhanced wave variability is a decrease in atomic oxygen, in-turn decreasing the electron density. LA TRUTH

16 Impact of COSMIC Observations on Ionosphere Specification CTL (mean=0.98) LA (mean = 0.98) LA+C (mean = 0.90) Assimilation of COSMIC observations leads to ~10% reduction in TEC error

17 Impact of COSMIC Observations on Thermosphere Specification Global U (~300 km) RMSE CTL LA LA+C Assimilation of COSMIC observations leads to minor improvement in thermosphere neutral winds

18 Impact of COSMIC Observations on Thermosphere Specification Global U, ~300 km LA LA+C CTL LA LA+C TRUTH Assimilation of COSMIC observations leads to minor improvement in thermosphere neutral winds

19 Summary Recent developments in WACCMX support whole atmosphere data assimilation, providing a global view of the troposphere, stratosphere, mesosphere, thermosphere, and ionosphere state. WACCMX+DART enables the seamless assimilation of observations from the troposphere to the thermosphere-ionosphere, which is critical for upper atmosphere specification and forecasting during periods of strong lower atmospheric forcing. Initial assimilation of COSMIC observations is promising, and demonstrates that they lead to an ~10% reduction in global TEC RMSE. Noise introduced by lower atmosphere introduces a bias in the ionosphere, impacting the assimilation of ionospheric observations and may also degrade thermosphere specification In collaboration with NCKU, the assimilation of ground-based TEC is being incorporated into WACCMX+DART and is anticipated to further improve the ionosphere specification. Plan to implement COSMIC-2 data assimilation in WACCMX+DART for both GPS RO and IVM observations.