LIDAR OBSERVATION OF THE 2014 KELUT VOLCANIC STRATOSPHERIC AEROSOLS AT KOTOTABANG , INDONESIA

The Kelut (Kelud) volcano (7.9S, 112.3E) in the Java island of Indonesia erupted on 13 February 2014. The CALIOP observed that the eruption cloud reached 26km above sea level. We have observed this stratospheric aerosol from 28 February 2014 at equatorial lidar site located in the Sumatra island of Indonesia (0.2S, 100.3E). We observed the depolarization maximum to be up to 2km below the backscatter maximum in April 2014. We also observed the vertical transportation process of stratospheric aerosol to troposphere by equatorial Kelvin wave.


INTRODUCTION
Stratospheric aerosols play important roles in climate regulation and atmospheric chemistry.The volcanic eruption of Mt.Pinatubo (15.14N, 120.35E) on 15 June 1991 injected huge amounts of SO2 and ash into the stratosphere.The Volcanic Explosivity Index (VEI) was 6.The eruption injected into the stratosphere an amount of SO2 estimated to be about 20 Tg [1].The injected SO2 was oxidized to sulfuric acid particles through homogeneous nucleation [2].Based on some satellite data, the stratospheric aerosol optical thickness (AOT) increased after 2000 as the result of a series of moderate but increasingly intense volcanic eruptions [3].
At 16:15 UTC, Mt.Kelut in East Java, Indonesia, erupted a mixture of gas, ash and water.The eruption was short lived and no subsequent explosions have been reported.VEI was 4. From CALIOP data, the inertial plume ejected material up to 26 km in the tropical stratosphere, but most of the plume remained at 19-20 km [4].A number of sensors continued to track the plume over the next few days.As the plume continued to move west over the Indian Ocean, it thinned and spread out, following local atmospheric circulation.Aerosol index returns show that much of the ash injected into the atmosphere was removed by three days after the eruption.The SO2 plume remained more coherent and could still be seen clearly in OMI and OMPS data 4 days after the eruption.OMI estimates suggest that SO2 is being removed from the plume at a rate of roughly 0.01 Tg per day.IASI data suggests that the removal is happening more rapidly, at a rate of 0.02 -0.03 Tg per day, however IASI reported higher initial concentrations of SO2 than OMI [5].Although most of the SO2 was injected into the stratosphere, the total SO2 mass measured was ~0.2 Tg (confirmed by multiple sensors including OMI, AIRS and IASI), making this eruption fairly modest in terms of SO2 release [6].
In this paper we report observations of stratospheric aerosols following the volcanic eruption of Mt.Kelut (7.9S, 112.3E) in February 2014 at lidar site in Kototabang (0.2S, 100.3E),Indonesia.

LIDAR SYSTEM
We had constructed the lidar facility for survey of atmospheric structure over troposphere, stratosphere, mesosphere and low thermosphere over Kototabang (100.3E,0.2S), Indonesia in the equatorial region [7].The lidar system consists of the Mie and Raman lidars for tropospheric aerosol, water vapor and cirrus cloud measurements, the Rayleigh lidar for stratospheric and mesospheric temperature measurements and the Resonance lidar for metallic species in the mesopause region.The most parts of this lidar system are remotely controlled via the Internet from Japan.The full lidar observations started from 2004.The routine observations of clouds and aerosol in the troposphere and stratosphere are continued now.We have installed DIAL (differential absorption lidar) system for highresolution measurements of vertical ozone profiles in the equatorial tropopause region in 2013 and We used the nearest operational radiosonde data to calculate the atmospheric molecular density.The lidar backscattered signal was interactively normalized to unity around 27-32 km, where aerosol-free conditions could be assumed.The total linear depolarization ratio d is defined as d= S/(P +S) x 100(%) where P and S are the parallel and perpendicular components of the backscattered signals [8].

RESULTS
Over Kototabang, stratospheric aerosol layers were observed on 28 February 2014 about 15 days after the eruption (Figure 1(a)).The peak values of scattering ratio was 4 at 19 km and the values of depolarization ratio was 4% at 19 km.Nonspherical ash particles were probably included in the layers with sulfuric acid particles that were produced from SO2 through chemical reactions.
Non-spherical particles were also present in the lower region (13-17km) of the aerosol layer.
On 29 April 2014 (2 months after the eruption), the peak altitude of scattering ratio move upward to 21 km but the peak altitude of depolarization ratio was still at 19 km (Figure 1

CONCLUSIONS
We have observed 2014 Kelut volcanic stratospheric aerosol from 28 February 2014 at equatorial lidar site located in the Sumatra island of Indonesia (0.2S, 100.3E).We observed the depolarization maximum to be up to 2km below the backscatter maximum in April 2014.We also observed the vertical transportation process of stratospheric aerosol to troposphere by equatorial Kelvin wave instability.
From CALIOP data, Kelut aelosol cloud movement of eastward by equatorial Kelvin wave was cleary seen.Aelosol layer was spread in the longitude direction with the lapse of time but the spread in the latitude direction is slower.
As the SO2 mass injected into the stratosphere by Kelut eruption is moderate, these observations are good example of transportation of materials from the equatorial stratosphere to the troposphere.
system for stratospheric aerosol monitoring in 2014.A polarizer divided photons at 2 into components parallel (P) and perpendicular (S) to the transmitted laser polarization plane.The received photons were converted to electrical signals by photomultiplier tubes (PMT).A photon counter is used to process the output signals of the PMTs.

Figure 1 Figure 2
Figure 1 Profiles of scattering ratio (dotted) and depolarization ratio (solid) on (a) 15 days after the eruption, (b) 2 months after the eruption, (c) 4 months after the eruption.