Coupling of sudden stratospheric warmings up to the mesosphere and lower thermosphere.
One of the most dramatic meteorological perturbations in the middle atmosphere is the sudden stratospheric warming (SSW). This usually occurs at least once per Northern winter and can result in large (up to 50K) temperature increases, wind reversals and hemispheric transport perturbations. It is now understood that the effects of SSWs resonate up to much higher altitudes, including the mesosphere (up to 90 km) and possibly even the thermosphere (above 90 km). However the actual manifestation of these SSWs on the mesospheric and lower thermospheric temperature structure remains uncertain, with different models yielding different answers, probably related to the treatment of gravity waves. We examine this question with the Navy's operational forecast system which has been extended up to the lower thermosphere. This model, NOGAPS- ALPHA (Advanced Level Physics High Altitude) has been used to perform several case studies of different SSW events over the last several years. The results will be compared with observations from two NASA satellites, TIMED and AURA, both of which are measuring the temperature from the stratosphere to the lower thermosphere. Two events will be emphasized and compared. The first is the unusual and prolonged disturbance of January-February 2006. The second is the shorter minor warming of 2008. Both SSW's had effects which resonated to high altitudes, but they were very different in their specific manifestations.
Interannual Variability in the Mesospheric Quasi-2 day Wave in the NOGAPS-ALPHA High- Altitude Data Assimilation System
NOGAPS-ALPHA is a global numerical weather prediction and data assimilation system extending from the surface to the upper mesosphere that combines a spectral forecast model with NAVDAS, the NRL Atmospheric Variational Data Assimilation System. NAVDAS is a 3DVAR system that assimilates conventional meteorological observations in the troposphere and lower stratosphere plus temperature soundings from both the Aura MLS (Microwave Limb Sounder) and SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instruments over the region from ∼100-0.006 hPa (∼16-80 km altitude). The resulting meteorological analyses extend from the surface to the upper mesosphere. The assimilation system has been run for the periods of January-February 2006 and 2008. Space-time spectral analysis of the 4-times daily NOGAPS-ALPHA mesospheric wind, temperature, and constituent fields show the global structure and time evolution of westward propagating zonal wavenumber 3 disturbances with periods near 2 days. Peak amplitudes of the quasi-two day wave in mesospheric temperature, meridional wind, and water vapor volume mixing ratio of 8 K, 40 m/s and 0.5 ppmv, respectively, occur during January 2006 in the extratropical summer hemisphere. During January 2008, the corresponding peak 2-day wave amplitudes are less than half of their 2006 values. Stratospheric warmings took place in both January 2006 and January 2008. Planetary wave forcing in the extratropical winter stratosphere leading up to these warmings has been shown to affect the growth and development of the quasi-two day wave in past modeling and observational studies. The NOGAPS- ALPHA analyses indicate that the stronger two-day wave amplitudes in January 2006 can be explained by enhanced planetary wave breaking throughout this period compared to January 2008 , which triggered inertial instabilities near the tropical stratopause that provided additional forcing for the global two-day wave mode.
Vertical Coupling Between the Stratosphere and Mesosphere During IPY
The International Polar Year (IPY) was an international scientific program focused on intensive observations in the Arctic and Antarctic from March 2007 to March 2009. As part of this effort, we present results of an NSF funded project, 'Pan-Arctic Studies of the Coupled Tropospheric, Stratospheric, and Mesospheric Circulation'. Planetary and gravity waves are mechanisms by which the troposphere is coupled to the stratosphere and mesosphere. When planetary wave amplitudes are large they break and form intense anticyclones that occasionally extend from the upper troposphere to the middle mesosphere. In addition, the Arctic polar vortex provides a means by which the stratosphere is coupled, both chemically and dynamically, to the troposphere below and the mesosphere above. Three-dimensional animations of the Arctic vortex and anticyclones will be shown to illustrate this vertical coupling during major stratospheric warming events that occurred in 2007-2008 and 2008-2009. An unprecedented stratospheric warming and subsequent mesospheric cooling event in January and February 2009 will be emphasized. Following the warming event the vortex in the upper stratosphere strengthened similar to 2004 and 2006; record cold temperatures were observed in the vortex near 45 km, mesospheric air rapidly descended in the vortex, and the separated polar winter stratopause soared above 80 km. Lidar temperature measurements at multiple Arctic sites taken during the events are interpreted based on the air masses in which the instruments measured. The vertical temperature structure varies considerably depending on whether the polar vortex or the Aleutian anticyclone was sampled. A web site http://research.iarc.uaf.edu/IPY-CTSM/index.php has been established as an archive of the daily dynamical evolution of the Arctic troposphere, stratosphere, and mesosphere during the two IPY winters. This site has been maintained in near-real time and thus has been a useful resource to coordinate the timing, and aid in the interpretation, of single-site observations of temperature and chemical constituents.
Simulation of the Impact of a Sudden Stratospheric Warming on the Upper Atmosphere Using a Whole Atmosphere Model
It is now abundantly clear that upper atmosphere space weather, in both neutral and plasma density, is forced by the Sun, the lower atmosphere, and a range of internal processes. EUV and plasma forcing from the Sun has been the focus historically, and is still a major challenge. In contrast, characterizing the influence from the lower atmosphere drivers is a more recent focus. The lower atmosphere is a source of gravity waves, planetary waves, and tides for the upper atmosphere. During a sudden stratospheric warming (SWW) event the planetary wave numbers one and two grow in the middle atmosphere changing the propagation of waves that influence the dynamics and temperature structure in the mesosphere and lower thermosphere. To characterize and understand the impact of lower atmosphere dynamics on the upper atmosphere a new Whole Atmosphere Model (WAM) has been developed as part of a collaborative project Integrated Dynamics through Earth's Atmosphere (IDEA) between the National Weather Service's (NWS) Space Weather Prediction and Environmental Modeling Centers, and the University of Colorado. WAM is a 150-layer general circulation model based on the NWS operational weather prediction Global Forecast System (GFS) model, which is coupled self- consistently with a Global Ionosphere Plasmasphere (GIP) physics model. An annual run of the WAM model has been performed after initialization, the output of which represents "climatological weather". Since IDEA includes all the layers of the atmosphere, the annual run of the model generates SSW naturally and realistically, without the need for changes in external forcing or boundary conditions. The model shows the classic signatures of a SWW with warming in the winter stratosphere and cooling in the winter mesosphere. In the lower thermosphere, high latitude warming occurs in agreement with recent observations from ground- based radar and from the TIMED satellite. The dynamics in the lower thermosphere is also altered inducing a change in low latitude dynamo electric fields. A SSW is just one example of how lower atmosphere sources introduce variability in the upper atmosphere, and can be used to illustrate the various coupling processes.
The Equatorial Ionosphere over Jicamarca during the January 2009 Sudden Stratospheric Warming
Last year we reported a high correlation between anomalous daytime ionospheric electric fields over Jicamarca and parameters associated with January 2008 Sudden Stratospheric Warming (SSW) event. Such distinct pattern in the equatorial drifts has been observed in previous SSW campaigns over Jicamarca, but the correlation was not as high as in the January 2008 event. Our results indicate that there is a strong coupling between the lower atmospheric processes related to the SSW events and the low-latitude ionosphere, however, the effects appear to be longitudinally dependent. In this work we present the eleven days of Jicamarca observations around the recent January 2009 SSW event. Besides obtaining vertical drifts from the incoherent scatter radar, this time we used a new mode that allows also the measurement of zonal drifts, electron density profiles, electron to ion temperature ratio, and mesospheric winds. In addition, we operated a new ionosonde called VIPIR in high time resolution. Our preliminary results indicate that indeed the equatorial ionosphere got disturbed during the SSW event, presenting again anomalous vertical drifts and therefore anomalous electron density values and profiles.
High Latitude Observations of the Mesosphere and Lower Thermosphere Associated with a Sudden Stratospheric Warming
We present observations with the Poker Flat Incoherent Scatter Radar (PFISR) located in central Alaska during the time period leading up to, concurrent with, and after a Sudden Stratospheric Warming in January and February 2008. Temperature fluctuations were observed that seem to be correlated with stratospheric motions and temperature changes. Temperature fluctuations at altitudes of 90-100 km seem to be out-of phase with the stratospheric warmings, with the cooling slightly preceding the warming. This result implies that the cooling is a result of upward mean motion forced from below, which is consistent with ion-velocity measurements (used as a tracer of the neutral gas at these altitudes). Examination of zonal and meridional winds also suggest enhanced lower thermospheric mean zonal winds during the main stratospheric warming period as well as a strong meridional semi-diurnal tide during the main stratospheric cooling period. These results suggest strong coupling of the lower thermosphere to stratospheric motions.
Ionospheric Variations During Sudden Stratospheric Warmings
We summarize ionospheric and thermospheric variations observed by the Millstone Hill incoherent scatter radar (42.6N, 288.5E) during stratospheric warmings of January 2008 and January 2009. Cooler ion temperature is observed in the F-region in January 2009, consistent with earlier reported observations of cooling during stratospheric warming in January 2008. The usual behavior of winter daytime electron density, dominated by TIDs with periods 1-1.5 hours, is replaced by a three-peak structure in electron density in January 2009. Plasma drift data indicate that this behavior is related to the vertical plasma motion, which in case of January 2009 data presents a mix of 8-10 hour waves with shorter (~2-3 hour) waves. Analysis of GPS TEC data indicates that variations in electron density are observed in a large range of longitudes and latitudes, with especially pronounced changes at low latitudes. We discuss what part of this variability could be associated with stratospheric conditions and what are the plausible mechanisms for such association.