Ki-Weon Seo

Surface mass balance contributions to acceleration of Antarctic ice mass loss during 2003–2013

Abstract Recent observations from satellite gravimetry (the Gravity Recovery and Climate Experiment (GRACE) mission) suggest an acceleration of ice mass loss from the Antarctic Ice Sheet (AIS). The contribution of surface mass balance changes (due to variable precipitation) is compared with GRACE‐derived mass loss acceleration by assessing the estimated contribution of snow mass from meteorological reanalysis data. We find that over much of the continent, the acceleration can be explained by precipitation anomalies. However, on the Antarctic Peninsula and other parts of West Antarctica, mass changes are not explained by precipitation and are likely associated with ice discharge rate increases. The total apparent GRACE acceleration over all of the AIS between 2003 and 2013 is −13.6 ± 7.2 Gt/yr2. Of this total, we find that the surface mass balance component is −8.2 ± 2.0 Gt/yr2. However, the GRACE estimate appears to contain errors arising from the atmospheric pressure fields used to remove air mass effects. The estimated acceleration error from this effect is about 9.8 ± 5.8 Gt/yr2. Correcting for this yields an ice discharge acceleration of −15.1 ± 6.5 Gt/yr2.

Evidence of the recent decade change in global fresh water discharge and evapotranspiration revealed by reanalysis and satellite observations

Variations of global evapotranspiration (ET) and fresh water discharge from land to oceans (D) are important components of global climate change, but have not been well monitored. In this study, we present an estimate of twenty years (1989 to 2008) variations of global D and ET derived from satellite remote-sensed measurements and recent reanalysis products, ERA-Interim and CFSR, by using a novel application of the water balance equations separately over land and over oceans. Time series of annual mean global D and ET from both satellite observations and reanalyses show clear positive and negative trends, respectively, as a result of modest increase of oceanic evaporation (Eo). The inter-annual variations of D are similar to the in-situ-based observations, and the negative trend of ET supports the previous result that relative humidity has decreased while temperature has increased on land. The results suggest considerable sensitivity of the terrestrial hydrological cycles (e.g., D and ET) to small changes in precipitation and oceanic evaporation.

Correlated error reduction in GRACE data over Greenland using extended empirical orthogonal functions

Surface mass change estimates from Gravity Recovery and Climate Experiment (GRACE) spherical harmonic solutions are contaminated by North-South stripe noise due largely to aliasing of high frequency variations into monthly samples. These meridional stripes are especially troubling for ice mass balance studies of the Greenland Ice Sheet (GrIS) where large ice mass variations are known to occur along North-South trending coastlines. By assuming that mass variations and noise have different patterns in both space and time over Greenland, we use Extended Empirical Orthogonal Functions (EEOF) to filter out this noise. The method is compared with a conventional approach, by examining both continent-wide estimates, and regional changes. GRACE results are compared with independent regional estimates derived from a climate model. The EEOF filter is effective at separating ice mass change signals from meridional stripe noise, with better rejection of high temporal frequency noise and less signal attenuation and spatial smoothing compared to a conventional method. We use EEOF filtered GRACE data to examine regional seasonal variations. Consistent with surface and other data, results show ice mass loss along the West, South-West and East coasts during summer and gain in these regions during winter. In addition, there is summer ice mass gain in the central region of the GrIS.

Global sea level change signatures observed by GRACE satellite gravimetry

Ice mass loss on land results in sea level rise, but its rate varies regionally due to gravitational self-attraction effects. Observing regional sea level rates by ocean mass change using the Gravity Recovery and Climate Experiment (GRACE) gravity solutions is difficult due to GRACE’s spatial resolution (~a few hundred km) and other limitations. Here we estimate regional sea level mass change using GRACE data (without contributions from temperature and salinity variations) by addressing these limitations: restoring spatially spread and attenuated signals in post-processed GRACE data; constraining ocean mass distribution to conform to the changing geoid; and judging specific corrections applied to GRACE data including a new geocenter estimate. The estimated global sea level mass trend for 2003–2014 is 2.14 ± 0.12 mm/yr. Regional trends differ considerably among ocean basins, ranging from −0.5 mm/yr in the Arctic to about 2.4 mm/yr in the Indian and South Atlantic Oceans.

Detection of Long Period Seismic Events by Using a Portable Gravity Meter, gPhone

Abstract: A gravity meter has been used for exploring subsurface mineral resources and monitoring long-period eventssuch as Earth tides. Recently, researchers found several other intriguing features that we could even detect largeteleseismic earthquakes and monitor seismic ambient noise using gravimeters. The zero-length spring suspensiontechnology gives the gPhone (Micro-g LaCoste) excellent low frequency sensitivity, which may have implications forinvestigating much longer-period natural events (e.g., Earth’s hum, tsunami waves, etc.). In this study, we presentpreliminary results through temporary operation of the gPhone at Geumsan in South Korea for 9 months (Nov. 2008-Jul. 2009). The gPhone successfully recorded large teleseismic events and showed a clear seasonal variation of the Doublefrequency microseisms during its operation period.Keywords: gPhone, Teleseismic earthquake, Double frequency microseisms요약: 중력계는 주로 지하 광물자원 탐사 및 지구조석과 같은 장주기 이벤트를 관측하는데 사용되고 있다. 최근 연구자들은 이 중력계를 이용하여 대형 원거리 지진 및 지진상시잡음 관측과 같은 몇몇 새롭고 흥미로운 사실들을 발견하였다. Micro-g LaCoste사의 gPhone에 적용된 zero-length spring suspension 기술은 초저주파 신호도 훌륭히 관측 가능하게하며, 이는 Earth’s hum이나 심지어 대형 지진해일 등을 관측하는데 큰 도움을 줄 수 있음을 시사한다. 이 연구에서는 충남 금산에서 2008년 11월 부터 2009년 7월까지 9개월간 임시로 설치/운영하였던 gPhone 자료를 분석하여 원거리 대형지진관측 및 상시지진잡음의 계절적 변화에 관한 사전결과를 보고하고자 한다.주요어: gPhone, 원거리 지진, 상시지진잡음

Refinement of GRACE Gravity Model Including Earth's Mean Mass Variations

The Gravity Recovery and Climate Experiment (GRACE) has observed the Earths mass redistribution mainly caused by the variations of groundwater, ice sheet, and sea level since its launch in April 2002. The global gravity model estimated by the GRACE observation is corrected by barometric pressure, and thus represents the change of Earth mass on the Earths surface and below Earths surface excluding air mass. However, the total air mass varies due to the water exchange between the Earths surface and the atmosphere. As a result, the nominal GRACE gravity model should include the Earths gravity spectrum associated with the total air mass variations, degree 0 and order 0 coefficients of spherical harmonics ( C00). Because the water vapor content varies mainly on a seasonal time scale, a change of C00 ( δ C00) is particularly important to seasonal variations of sea level, and mass balance between northern and southern hemisphere. This result implies that δ C00 coefficients should be accounted for the examination of continental scale mass change possibly associated with the climate variations.

Installation of Very Broadband Seismic Stations to Observe Seismic and Cryogenic Signals, Antarctica

Korea Polar Research Institute (KOPRI) has successfully installed two autonomous very broadband three-component seismic stations at the King George Island (KGI), Antarctica, during the 24th KOPRI Antarctic Summer Expedition (2010 ~ 2011). The seismic observation system is originally designed by the Incorporated Research Institutions for Seismology Program for Array Seismic Studies of the Continental Lithosphere Instrument Center, which is fully compatible with the Polar Earth Observing Network seismic system. The installation is to achieve the following major goals: 1. Monitoring local earthquakes and icequakes in and around the KGI, 2. Validating the robustness of seismic system operation under harsh environment. For further intensive studies, we plan to move and install them adding a couple more stations at ice shelf system, e.g., Larsen Ice Shelf System, Antarctica, in 2013 to figure out ice dynamics and physical interaction between lithosphere and cryosphere. In this article, we evaluate seismic station performance and characteristics by examining ambient noise, and provide operational system information such as frequency response and State-Of-Health information.