2008 Workshop:Coupling of atmospheric regions during stratospheric sudden warmings
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Coupling of atmospheric regions during stratospheric sudden warmings
Contents |
Location
Davos
Date/Time
1600-1800 Friday 20 June 2008
Conveners
Format of the Workshop
scheduled short-presentations and discussions
Duration
2 hours (default)
Estimated attendance
50
Conflicts with other workshops
Ground-Space Models for Studying Atmospheric Coupling (Han-Li Liu, Dave Siskind, Bob Schunk)
Lower-Upper Atmosphere Coupling (Dave Fritts, Mike Taylor)
MLT Science Involving Lidars (Dave Fritts, Gary Swenson, Joe She, Xinzhao Chu)
Other MLT science
Special technology requests
none
Forum
Comments, Questions, Discussion Forum
Brief Initial Description
Recent research advances present new evidence of strong vertical coupling between different atmospheric regions. Multiple reports show variations in the mesosphere-thermosphere-ionosphere system related to such disparate phenomena as earthquakes, tsunami, thunderstorms or stratospheric sudden warmings. The goal of the workshop is to examine most recent experimental and modeling results related to such coupling, with particular emphasis on coupling during stratospheric sudden warmings.
A stratospheric sudden warming (SSW) is a dramatic large-scale event in the winter middle atmosphere lasting several days or weeks. It involves profound changes in temperature and wind system, with > 15 K warming at stratospheric altitudes and 20-50 K cooling at mesospheric altitudes. Simulations of SSW events predict 20-30 K warming in the lower thermosphere. Currently there is very little experimental evidence of variations in the thermosphere or ionosphere, though significant part of day-to-day variability in thermospheric and ionospheric parameters is thought to be related to coupling from lower altitudes. In order to extend studies of SSW effects to higher altitudes, a specially designated ISR World Day campaign was arranged during a very large SSW event in January 2008, when warming at stratospheric heights has reached or exceeded a 30-year record. This workshop will provide a forum where researchers can present their experimental and modeling results and address the SSW coupling challenges.
Presentation Resources
Upload presentation and link to it here. Links to other resources.
Chau et al. -> Evidence of SSW effects over Jicamarca Ionosphere
Agenda
Larisa Goncharenko (introduction)
Richard Collins (lidars)
Peter Hoffmann (MF/MR radars)
Michael Gerding (Lidar)
Han-Li Liu (TIMEGCM)
Chihoko Yamashita (TIMEGCM)
Irfan Azeem (MF radars)
Tao Yuan (lidar)
David Siskind (TIMED/SABER)
Jorge Chau - Jicamarca ISR
Tony van Eyken - Svalbard, EISCAT ISR
Mike Nicolls & Anja Stromme – PFISR, Sondrestrom
Larisa Goncharenko - Millstone Hill ISR, PFISR
Mike Sulzer - Arecibo ISR
Workshop summary
This workshop presented an opportunity for the CEDAR research community to review recent results related to variability in the mesosphere, lower and upper thermosphere and ionosphere during stratospheric sudden warmings (SSW).
Large variability in the MLT region is evident during SSW from both observations and numerical simulations. High latitude Rayleigh lidar data (Rich Collins, University of Alaska) indicate “elevated stratopause” (cooling at ~40-60km and warming at 65-75km) as well as decrease in the gravity wave activity during January 2004 SSW. South Pole Station rotational temperature data (Irfan Azeem, Embry-Riddle Aeron. Univ.) show mesopause cooling prior to 2002 SSW and concurrent abatement of gravity wave activity. As highlighted by Peter Hoffmann (Leibniz-Institute of Atmospheric Physics, Germany), mesospheric response to stratospheric warming events includes downward propagation of the wind reversal (i.e. stratwarming starts earlier in the mesosphere than in upper stratosphere) and reduced gravity wave activity and energy dissipation rate in the MLT region, which is consistent with the mesospheric cooling. Mid-latitude (54N, 12E) lidar data (Michael Gerding, Leibniz-Institute of Atmospheric Physics, Germany) shows average mesospheric cooling of the order of ~50% of stratospheric warming and a change in the altitude distribution of wind field from winter to summer-type pattern. As reported by Titus Yuan, mid-latitude lidar data (40oN, 105W) during January 2008 SSW indicates stronger westward and northward mean winds, increase in the 24-h diurnal tide for the meridional component and 12-h tide for the zonal component. Observations by Aura/MLS and TIMED/SABER (David Siskind, NRL) showed large temperature variation at high latitudes from the stratosphere to the lower thermosphere during the 2005-2006 major SSW, including an “elevated stratopause” around the peak warming. This feature is reproduced by a TIME-GCM/ECMWF simulation of this time period. Han-Li Liu (NCAR) presented analysis showing that the interaction between gravity wave and mean wind during the SSW is responsible for the observed temperature change in the MLT region, and that the “elevated stratopause” is caused by adiabatic warming, driven primarily by a westward gravity wave forcing, that initially started in the lower thermosphere in the early stage of SSW. The westward forcing, thus the adiabatic warming, descends after the peak warming as the eastward jet in the MLT weakens. Results from TIME-GCM and NOGAPS-ALPHA (David Siskind, NRL) simulations demonstrate the sensitivity of MLT variability to gravity wave parameters. SSW events could therefore be good cases for constraining gravity wave parameterization.
According to observations, gravity wave variance also changes during SSW. Chihoko Yamashita (NCAR student) analyzed the gravity wave variance change in the stratosphere and MLT using the TIME-GCM simulation of the 2002 Southern Hemisphere SSW. According to this analysis, the gravity wave variance peaks before the maximum warming in the stratosphere and after the peak warming in the MLT. The former is in general agreement with previous stratospheric observations. In the MLT region, however, observations have suggested decrease of variance. Analysis of model results also showed large spatial variability of the gravity wave variance in both stratosphere and mesosphere. This corroborates with Rich Collins results, indicating large spatial variability in the vortex structure during SSW. This has important implications for interpreting data from single site ground based observations.
Presentations by Koki Chau (Jicamarca), Mike Sulzer (Arecibo Observatory), Larisa Goncharenko (MIT, Haystack Observatory), Mike Nicolls (SRI International), Anja Stromme (SRI International) and Tony van Eiken (EISCAT Association) summarized observations by incoherent scatter radars during the January 2008 World Day campaign and all suggest that SSW may impact the ionosphere. At low latitude (Koki Chau, Jicamarca), a profound change in electric field occurred during the January 2008 SSW, January 2003 SSW and December 2000 SSW. This change includes significant increase in the F region vertical drift in the early morning and decrease in the afternoon. The F-region peak electron density is decreased due to a redistribution of electron density. At lower mid-latitude (Michael Sulzer, Arecibo), preliminary analysis of selected days indicates unusually strong daytime electric field and a daytime “collapse” of F-region electron density. Analysis of data at middle and high latitudes was focusing on SSW signatures in ion temperature. As presented by Larisa Goncharenko (Haystack Observatory, MIT), a cooling in the large altitude range (150-300km) and warming in a narrow altitude band (120-140km) was observed during stratospheric warming of January 2008 at middle latitude. The lower thermospheric warming is consistent with TIMEGCM predictions, albeit it is observed at lower latitude. At the high latitude, PFISR data (Michael Nicolls, SRI International) show cooling at 80-100km, which is consistent with previous mesospheric observations, as well as increased winds in the lower thermosphere. As indicated by Anja Stromme (SRI International) and Tony van Eiken (EISCAT), ionospheric parameters at high latitudes (EISCAT, Svalbard, Sondrestrom, PFISR radars) are strongly controlled by magnetospheric drivers, and search for SSW effects is more complicated than at lower latitudes.
The associated discussion indicated that although previous observational and numerical studies have suggested change of lower thermosphere temperature, O, and E region electron density, coupling with electrodynamics has not been explored. It was also recognized during discussion that both the Millstone Hill and Arecibo radar show large semi-diurnal signatures around the maximum warming in 2008.
From the presentations and the discussions, there are interests to further pursue the following issues:
1. The 2008 SSWs are well observed thanks to the IS radar observation campaign. This campaign also coincides with the 4-th Tidal Campaign (Dec 2007 – Jan 2008). This gives us an excellent opportunity to study the lower and upper atmosphere coupling. Numerical simulation using TIME-GCM is being planned for this time period.
2. What is responsible for the difference between observation and model simulation regarding gravity wave variance? What is a proper interpretation of the reduction of radar spectral width during SSW: decrease in temperature or decrease of turbulence intensity?
3. A challenge for the observational community is to determine the change in gravity wave characteristics and gravity wave momentum flux during SSW.
4. How different ionospheric and thermospheric parameters (winds, electric field, temperatures, electron density) respond to SSW? How the ionospheric response vary in time in relationship to SSW (lead or delay)? How does it vary with latitude/longitude?
5. The coupling with the ionosphere and electrodynamics will be explored using both observational and numerical results. What caused the ionosphere electron density “collapse” as observed by Arecibo ISR? Does semi-diurnal tide play a role? Is it related to SSW?
