Mechanism of 2006 Augustine Eruption leading to Sudden Stratospheric Warming and Cyclogenesis

Mechanism of 2006 Augustine Eruption leading to Sudden Stratospheric Warming and Cyclogenesis.
On January 11, 2006 the Augustine volcano located in the Cook Inlet of Alaska entered its explosive phase of eruption sending a column of ash and steam upwards 6.5km at 4:44am and another 10.2km into the stratosphere at 5:12am. Wallace et al. These two events are the preliminary round continuing through January 28th of thirteen events culminating in a cumulative erupted volume of 149 million cubic yards (magma) and inflated eruptive volume of 58 million cubic yards (tephra & pyroclastic flows). Coombs et al. Volume of tephra fall alone was 28 million cubic yards for all 13 events. Mass of tephra fall was based on mass eruption rate for event 9 on January 17th: 6.9 x10⁶kg/s. The eruption of event 9 sent a column of ash and 13.5km into the stratosphere steam on the morning of January 17th at 7:58 am. A volcanic explosivity index (VEI) of 3 was assigned by USGS scientists Wallace et al. based on plume height and tephra fall.
PlumeRise, the Bristol model of volcanic plumes in a wind field was used to define event 9 of the 2006 Augustine eruption. Woodhouse et al. Data generated by PlumeRise model was very useful in supporting a comparison between event 9 and MERRA data (Modern Era Retrospective-Analysis for Research and Applications data for two levels of stratosphere). Annual Meteorological Statistics for the Northern Hemisphere (NASA). Data for two levels of stratosphere, 50hPa & 10hPa for the period January 1st to March1st were downloaded and compared with PlumeRise data. MERRA data for the parameters of zonal wind velocity (U), heat flux (VT), momentum flux (UV), Z1 & Z2 waves of geopotential heights were plotted against daily mean values of the AO (arctic oscillation). Sample sets were selected for expected trends of sea level pressure versus MERRA data. Correlations were found between each set of MERRA variables and AO variables. Scatterplots were made with transformed data to illustrate slope of trend lines. Transformation did not change correl coefficient or skew. The momentum flux along the centreline trajectory in the plume (UV) of the 2006 Augustine eruption reached a maximum of 1.9e3kg /ms² at 9313 meters on Jan 17th. See plumedata. Two days later on Jan 19th MERRA data indicates momentum flux (UV) 45 -75°N, a vector quantity between meridional and zonal wind speeds and direction generally poleward, reached a maximum (270 m^2/s^2). See AOvsMERRA10hPaAugJ06data1 in Appendix.
Minimum temperatures (Tmin) at 10hPa (lower stratosphere) 50-90 N rose steadily following event 9 eruption from a low of 196.27K to a high of 206.69K on Jan 27th, three days before SSW. Kinematic heat flux 45-75 N reached a peak 257 Km/s at 10hPa on Jan 20th, three days after event 9 eruption. True heat flux (Ht) from eruption at 9303m (270hPa) is 6.58e6Watts/m2 derived from plumerisedata. To evaluate the magnitude of the volcanic heat flux in comparison to kinematic heat flux involves the derivation of MERRA heat flux (Vk) 33.7 Km/s into true heat flux (Vt). Assuming atmospheric values of specific heat (1006 J/K kg) and density (0.236 kg/m3)at 150hPa: Vk x Cp x β = Vt = 8.0e3 W/m2. Direct solar radiation from 45-75N ranges from 168 to 50 W/m2 during January, Pacific Northwest and Anchorage respectively. Vt derivation is 48 times greater than 168W/m2. Volcanic heat flux is 2.25e6 W/s² at 150hPa, 280 times greater than atmos. MERRA flux 45-75N. Volcanic heat flux of this magnitude impacts the jetstream and slows down zonal winds considerably. MERRA kinematic heat flux 45-75 N peaks at 257K m/s on Jan 20th, three days after event 9 eruption. See heatfluxcalc & heatfluxdecay (Plumerise folder).
Zonal wind (U) at 60N slows on Jan 20th and goes negative (easterly) on Jan 21st, reaching a peak -26.15m/s five days before SSWon Jan30th, remaining easterly for twenty five consecutive days. SeeMERRA10hPaJ06data.
The volume of entrained air in the plume was 1.6e11m³at tophat (top of plume) with a power of 115 e12 Joules per second. The total power generated 225 meters (1477m asl) above the crater is 15 TW equivalent to the power generated by 5 “average Atlantic” hurricanes (3TW). At 3148 meters asl., 1896m above the crater 30TW power generated is equivalent to a “Pacific super typhoon” Emanuel, K. A., (1999) The mass of steam, gases, ash above the crater is initially propelled at 5.3 times the speed of sound from the conduit. Petersen et al. The tremendous amount of heat contained in steam and ash entrains a massive amount of air from the ambient atmosphere, the volume of the plume increased by 352 times from crater to tophat. At 9.3 km asl, above the tropopause, momentum flux is at a peak and power generated is 101TW. At tophat 12.2 km power generated is 115TW equivalent to the power of 38 hurricanes or 3.8 super typhoons. The explosion of event 9 generated an upward propagating gravity wave into the stratosphere. The University of Alaska Infrasonic Array at Fairbanks detected a series of 12 infrasonic signals from the 2006 Augustine eruption occurring Jan 11 through the 28th. Olson et al. These signals were determined to have passed through the stratosphere and thermosphere on the way from Cook Inlet to Fairbanks, a distance of 675 km (sea level). The signals consisted of wave trains with period of three to ten minutes, in the range of gravity waves. Observed signal times correspond with explosive events on dates Jan 11, 13, 14, 17 and 28 as noted in Table 1 Olson et al & Table 4 of Chapter 9 USGS report Wallace et al. The shock waves of events 1-10 deposit kinetic energy and a ripple effect to the Rossby waves of the jetstream. It is evident by examining the waves of the 200mb upper wind analysis that a volcanic signal of the 2006 explosive events has an impact on the jetstream. An orange star is placed at the location of the Augustine eruption on each map. Spaces between isotachs widen (winds slow) and ripple where there is a star. The explosive events slow the winds aloft, amplify the low pressure at the surface and cause divergence aloft. The trough over North America to the east of the disturbance deepens strongly after event 9. Wave breaking can be seen over the Caspian Sea (1/13), Greece (1/14) and Europe (1/15). Wave blocking is evident over Kamchatka and Europe (1/27) & Siberia (1/30).
Volume of event 9 eruption plume was calculated using data derived from PlumeRise model and USGS reports. See Plumerisecalc & Plumerisepix. Volume of plume was calculated from a series of cones and conic sections. Volume data was put into Kineticenergy worksheet to calculate mass of plume at elevations and translational energy (Kt)upward. The upward thrust of energy Kt=½mu², accounted for less than 2% of total kinetic energy (KE) and a mean of less than 0.5%. Rotational kinetic energy (Kr) accounted for at least 98% at any elevation. Kr=½ Iω ² was calculated in steps. First, v= usinθ: tangential velocity at point on radius equals vertical velocity times sin of angle 360/2π. Second, angular velocity ω=v/r: tangential velocity/ radius. Third, vorticity of plume, angular acceleration: ω². Fourth, W/ω=τ: Watts/ angular velocity = torque. Fifth, I=τ /ω²: torque/ vorticity= inertia. Sixth, τ=Iω²: inertia x vorticity= torque. Skip step 6 & go to Kr=½ Iω ² or skip step 5 and go to Kr= τ/2. Total KE generated at ~300mb just below tropopause ~1.16PetaJoules, just above tropopause ~1.36PJ & ~3.7PJ at 200mb. The impact of an immense mass of air 8.6Megatonnes at 9253 m ~300mb deposits kinetic energy and puts a ripple in the Rossby wave. The ripple is amplified as it rises with less pressure in the atmosphere. Above 12.2 km the plume loses buoyancy and the cold mass 47 Megatonnes of air falls vertically and in a generally southwest direction by latitude with 176PJ kinetic energy. A deep trough in the Rossby wave develops directly after event 9 eruption as the cold mass of air falls.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s