Weather Radar systems for mitigation of volcanic cloud hazards to aircraft Keflavik, Iceland Based on paper by C. Lacasse, S. Karlsdóttir, G Larsen, H Suusalu, W I Rose and G G J Ernst, 2003 Weather radar observations of the Hekla 2000 eruption cloud, Iceland, Bulletin of Volcanology 66: William I Rose Michigan Technological Univ Fall 2009 Ashfall Graduate Class lecture

Meteorological Radar Systems are designed to detect “large” (raindrop-sized) particles such as those found in thunderstorms. They are pulsed, active remote sensing systems which send and receive electromagnetic radiation with wavelengths of cm. The strength of radar return from a cloud is measured in dBz, a unit which is based on relative numbers of mm sized raindrops in a specific volume of cloud. Large particles produce MUCH stronger returns than small ones--the relationship scales to the SIXTH POWER of the radius. The detection is excellent for particles that are cm sized, and very poor for particles smaller than 1 mm….

Explosive Eruption +15 sec.+30 sec. +40 sec. +60 sec.+5 min.

Eruption Column Rise

Ash Fall Rate

Volcanic Clouds can only be distinguished by radar if large particles are present. But such particles must fall quickly… So radar mapping becomes problematic after the volcanic cloud is more than 30 min old and the large particles have fallen out. Practical Strategy: Use the radar during eruption and immediately after it. Obtain height information and determine the direction and speed of movement. Then, if you wish to track it after that--you need another tool (eg infrared satellite data).

Schneider et al, 1995, USGS Bull 2139: Sept 17-20, 1992

2000 Eruption of Hekla Hekla –Elongate Shield Volcano –Regular series of eruptions (1845, 1947, 1970, 1980, 1991) –Began eruption on Feb 26, 2000 at 1800 UT –Silicic explosive onset to eruptions –Brief explosions followed by fissure fed lava flows Explosive onset Fissure activity and lava flows--main phase Older Hekla silicic fall deposits

26 Feb UT Ground view of Hekla eruption column, as seen from Vik, Iceland, ~67 km SSE of the volcano (J. Erlendsson)

Remote sensing of the brief explosive phase of the eruption shows development of cold cloud with shadows, winds and temperatures reflecting the tropopause. DMSP VIS 2/26/ UT shadow Rose et al, 2003, AGU Geophys Monograph 139

Range-height diagram for Keflavik radar, applicable during the Hekla eruption. Shaded region shows detection limits.

The maximum height limit set on the Keflavik radar was determined based on meteorological, not volcanological criteria. Although there may be advantages during routine operations when there is no eruption, this decision unfortunately limited the ability of the radar to measure the maximum height of the eruption cloud. The farther the volcano is from the radar, the more the minimum height is affected---this is due to curvature of the earth. Thus the early onset of explosive eruptions will be missed for more distant volcanoes. The overall maximum range of the radar is listed at 480 km, but practically this is an overestimate, because of curvature.

100 km Hekla Vertical Maximum Intensity VMI “normal” before erupttion

Keflavik Radar 26 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology Hekla

Keflavik Radar 26 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 27 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 27 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 27 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 27 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 27 Feb UT VMI normal Lacasse et al, 2004, Bull Volcanology

Volcanic cloud rose quickly during eruption and expanded to the NE for several hours. The strength of the radar return is high (>60 dBz)--values that are consistent with very large raindrop-sized particles (lapilli). We expect this radar return to decay quickly (~30 min) from inevitable ash fallout as soon as the eruption wanes. In this case, the eruption wanes, but the radar reflection does not decline as quickly as expected… We infer that residual fine ash, still in the drifting cloud, but not itself detectable by radar, is nucleating ice formation and this process preserves the radar signal longer.

Hekla

Keflavik Radar 26 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology Hekla

26 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology Keflavik Radar

26 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 26 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 27 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 27 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 27 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 27 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Keflavik Radar 27 Feb UT EchoTop Lacasse et al, 2004, Bull Volcanology

Here successive radar images are used to measure the advancing, advecting volcanic cloud, reflecting the dispersion by winds. At left 4 successive images are superimposed with the leading edge of 15 dBz. At right are maps made from such images

Here a radar map 2 hrs after the eruption onset is compared with an ashfall map. They are similar, but ashfall occurred slightly westward of the radar position. We infer that the ash was advected westward during its fall through the troposphere by winds.

Radar observations, 26 February 2000, eruption of Hekla Column Height > 12 km Most Explosive Eruption duration 1-2 hrs, correllates with seismic record Cloud drifts to NNE, m/sec Radar reflections range up to >60 dBz above the volcano, fade after a few hours to near 0 Downwind portion of the volcanic cloud fades slowly, reflecting ice nucleation by finer ash Fallout of ash occurs in area which reflects advection of falling ash by lower level winds

Other references about radar detection of volcanic clouds Marzano, F S, G Vulpiani and W I Rose, 2006, Microphysical Characterization of Microwave Radar Reflectivity due to Volcanic Ash Clouds, IEEE Transactions on Geoscience and Remote Sensing 44: Marzano, F S, S Barbieri, G Vulpiani and W I Rose, 2006, Volcanic ash cloud retrieval by ground-based microwave weather radar, IEEE Trans on Geoscience and Remote Sensing 44:

Weather Radar online

The February-March 2000 Eruption of Hekla, Iceland from a satellite perspective W I Rose, Y Gu, I M Watson, T Yu, GJS Bluth, A J Prata, A J Krueger, N Krotkov, S Carn, M D Fromm, D E Hunton, G G J Ernst, A A Viggiano, T M Miller, J O Ballentin, J M Reeves, J C Wilson, B E Anderson and D E Flittner 2003, AGU Geophysical Monograph 139 (ed by A Robock and C Oppenheimer) A detailed study of the Hekla volcanic cloud was made using satellite remote sensing methods and was reported in a paper published last year…

Total mass of fine particles in the Hekla volcanic cloud peaks at ~ 10^6 tonnes and decreases after 10 hours.

28 Feb UT 7.3  m 0.16 Tg8.6  m Tg

Eruption Summary Magma erupted: 0.11 km 3 = 3 x 10 5 Tg, mostly long after explosive phase Ice in stratospheric cloud = 1 Tg SO 2 in stratospheric cloud kT (MODIS 7.3 and 8.6) Sulfate in stratospheric cloud 3-5 kT Fine ash mass ~100 kT --only detected in first hour