Ice Mass Variations Research Articles

Overview and sample applications of SMILES and Odin-SMR retrievals of upper tropospheric humidity and cloud ice mass

Abstract. Retrievals of cloud ice mass and humidity from the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) and the Odin-SMR (Sub-Millimetre Radiometer) limb sounder are presented and example applications of the data are given. SMILES data give an unprecedented view of the diurnal variation of cloud ice mass. Mean regional diurnal cycles are reported and compared to some global climate models. Some improvements in the models regarding diurnal timing and relative amplitude were noted, but the models' mean ice mass around 250 hPa is still low compared to the observations. The influence of the ENSO (El Niño–Southern Oscillation) state on the upper troposphere is demonstrated using 12 years of Odin-SMR data. The same retrieval scheme is applied for both sensors, and gives low systematic differences between the two data sets. A special feature of this Bayesian retrieval scheme, of Monte Carlo integration type, is that values are produced for all measurements but for some atmospheric states retrieved values only reflect a priori assumptions. However, this "all-weather" capability allows a direct statistical comparison to model data, in contrast to many other satellite data sets. Another strength of the retrievals is the detailed treatment of "beam filling" that otherwise would cause large systematic biases for these passive cloud ice mass retrievals. The main retrieval inputs are spectra around 635/525 GHz from tangent altitudes below 8/9 km for SMILES/Odin-SMR, respectively. For both sensors, the data cover the upper troposphere between 30° S and 30° N. Humidity is reported as both relative humidity and volume mixing ratio. The vertical coverage of SMILES is restricted to a single layer, while Odin-SMR gives some profiling capability between 300 and 150 hPa. Ice mass is given as the partial ice water path above 260 hPa, but for Odin-SMR ice water content, estimates are also provided. Besides a smaller contrast between most dry and wet cases, the agreement with Aura MLS (Microwave Limb Sounder) humidity data is good. In terms of tropical mean humidity, all three data sets agree within 3.5 %RHi. Mean ice mass is about a factor of 2 lower compared to CloudSat. This deviation is caused by the fact that different particle size distributions are assumed, combined with saturation and a priori influences in the SMILES and Odin-SMR data.

GRACE RL05-based ice mass changes in the typical regions of antarctica from 2004 to 2012

Abstract: The Antarctic ice sheet is the largest block of ice on Earth, a tiny change of its ice sheet will have a significant impact on sea level change, so it plays an important role in global climate change. The Gravity Recovery and Climate Experiment (GRACE) mission, launched in 2002, provides an alternative method to monitor the Antarctic ice mass variation. The latest Release Level 05 (RL05) version of GRACE time-variable gravity (TVG) data, derived from GRACE observations with improved quality and time-span over 10 years, were released by three GRACE data centers (CSR, JPL and GFZ) in April 2012, which gives us a chance to re-estimate the ice mass change over Antarctic more accurately. In this paper, we examine ice mass changes in regional scale, including Antarctic Peninsula (AP, West Antarctica), Amundsen Sea Embayment (ASE, West Antarctica), Lambert-Amery System (LAS, East Antarctica) and 27 drainage basins based on three data sets. The AP mass change rates are − 12. 03±0. 74 Gt/a (CSR, 2004–2012), − 13. 92±2. 33 Gt/a (JPL, 2004 − 2012), − 12. 28±0. 76 Gt/a (GFZ, 2005-2012), with an acceleration of − 1.50±0. 25 Gt/a 2 , − 1.54 ± 0. 26 Gt/a 2 , − 0. 46±0. 28 Gt/a 2 respectively, the ASE mass change rates are − 89. 22±1. 93 Gt/a, − 86. 28 ± 2. 20 Gt/a, − 83. 67±1. 76 Gt/a with an acceleration of − 10. 03±0. 65 Gt/a 2 , − 8. 74±0. 74 Gt/a 2 and -5. 69 ± 0. 68 Gt/a 2 , and the LAS mass change rates are − 4. 31±1. 95 Gt/a, − 7. 29±2. 84 Gt/a, 1. 20±1. 35 Gt/a with an acceleration of − 0. 18±0. 62 Gt/a 2 , 3. 55±0. 95 Gt/a 2 and 0. 97±0. 49 Gt/a 2 . The mass change rates derived from the three RL05 data are very close to each other both in AP and ASE with the uncertainties much smaller than the change rates, and mass losses are significantly accelerated since 2007 in AP and 2006 in ASE, respectively. However, the mass change rates are significantly different in LAS, negative rate from CSR and JPL data, but positive rate from GFZ data, the uncertainties are even larger than the correspondent change rates. With regard to the 27 drainage basins, seven basins (basin 3–9) located in the east Antaxctica show positive mass change rates, and the rest twenty basins are chamcterizecl by negative mass change rates during the time span of the three RL05 data.

Northern PMC brightness zonal variability and its correlation with temperature and water vapor

AbstractPolar mesospheric clouds (PMCs) measured by the Cloud Imaging and Particle Size instrument on the AIM satellite show strong zonal asymmetries, with prominent planetary‐scale variations. The correlations between zonal variations of cloud brightness and temperature or water vapor (H2O) are determined in different stages of the PMC season. Aura Microwave Limb Sounder measured temperature and water vapor are used in the analysis. A zero‐dimensional (0‐D) PMC model was used to interpret the observation. Analyses of all days of the five northern seasons from 2007 to 2011 indicate that temperature and albedo daily zonal variations are anticorrelated in the season start and end, whereas in the core of the season the correlation is relatively poor. The albedo and H2O correlation in the zonal direction is poor throughout the season. Zero‐dimensional model physics indicates that when clouds are weaker, or the environment is warmer and drier, temperature plays an increasingly important role in determining the cloud ice mass variation, which explains the stronger correlation of temperature and albedo at the start and end of the season. Water vapor takes a strong role in determining the ice mass variation in the core of the season when the clouds are stronger and the environment is colder and wetter. However, on a daily basis the H2O depletion associated with the ice production will lead to significant shift of the ice maxima and “post‐ice” H2O maxima in the zonal direction, which leads to the poor correlation between the observed H2O and albedo.

Bedrock displacements in Greenland manifest ice mass variations, climate cycles and climate change

The Greenland GPS Network (GNET) uses the Global Positioning System (GPS) to measure the displacement of bedrock exposed near the margins of the Greenland ice sheet. The entire network is uplifting in response to past and present-day changes in ice mass. Crustal displacement is largely accounted for by an annual oscillation superimposed on a sustained trend. The oscillation is driven by earth's elastic response to seasonal variations in ice mass and air mass (i.e., atmospheric pressure). Observed vertical velocities are higher and often much higher than predicted rates of postglacial rebound (PGR), implying that uplift is usually dominated by the solid earth's instantaneous elastic response to contemporary losses in ice mass rather than PGR. Superimposed on longer-term trends, an anomalous 'pulse' of uplift accumulated at many GNET stations during an approximate six-month period in 2010. This anomalous uplift is spatially correlated with the 2010 melting day anomaly.

Expected improvements in determining continental hydrology, ice mass variations, ocean bottom pressure signals, and earthquakes using two pairs of dedicated satellites for temporal gravity recovery

[1] The Gravity Recovery and Climate Experiment mission has demonstrated the ability to quantify global mass variations at large spatial scales with monthly to sub-monthly temporal resolution. Future missions of this type taking advantage of improved measurement technologies will be limited by temporal aliasing errors. We suggest the addition of a second pair of satellites to reduce these errors. Using an optimized mission architecture consisting of a polar pair of satellites coupled with a lower inclined pair of satellites (72°), both in 13-day repeating orbits, we quantify the expected scientific improvements that having two pairs of satellites will provide over one pair. Numerical simulations to spherical harmonic degree 100 are run over one full year. Analysis using empirical orthogonal functions reveals that two satellite pairs determine annual mass variations in small basins which are undetected using one pair of satellites. Averaging kernels are used to show that two satellite pairs offer an 80% reduction in the level of error in determining mass variations in 53 hydrological basins and 12 Greenland basins over the year. After standard GRACE post-processing techniques have been applied to the one-pair solutions, it is seen that two satellite pairs (with no post-processing) still offer a 25%–75% improvement in determining the mass variations. Spatiospectral localization analysis is used to show increased spatial resolution and higher signal-to-noise ratios in recovering hydrology in the Amazon River basin, ocean bottom pressure signals in the Southeast Pacific basin, and a simulated earthquake signal representative of the 2010 Maule, Chile earthquake.

Past and present-day ice mass variation on Svalbard revealed by superconducting gravimeter and GPS measurements

[1] We use Superconducting Gravimeter (SG) and Global Positioning System (GPS) measurements from Ny-Alesund, Svalbard, to infer changes in ice mass loss between September 1999 and September 2010. We find that during this period, the gravity rate and vertical crustal velocities are changing with time, adding to evidence about varying rates of ice mass loss. The gravity rate varies through 10 years of observation; −0.23 μGal/yr in 2000–2002, −3.22 μGal/yr in 2002–2005 and −1.10 μGal/yr in 2005–2010. The gravity changes agree well with the observed uplift rates measured by GPS, which are 4.4, 11.3 and 7.4 mm/yr, over the same periods. In addition, we generate model predictions which account for past and present-day ice mass variation. We find that the models under predict both the observed uplift rates and gravity changes.

The ice sheet height changes and mass variations in Antarctica by using ICESat and GRACE data

The Gravity Recovery and Climate Experiment (GRACE) satellite mission has provided the monthly earth's gravity field models since August 2002, from which the mass variations in Antarctica can be estimated. Because of the very low-degree spherical harmonic coefficients, especially the degree-2 zonal term J2 are not well determined by GRACE, more attention should be paid on the effects of J2 when the earth's mass variations are derived from spherical harmonic coefficients. To see the differences more clearly, wavelet transformation is applied to the J2 time series derived from GRACE measurements by different agencies, such as Centre National d’Études Spatiales/Groupe de Recher de Deodesie Spatiale, GeoForschungsZentrum Potsdam, University of Texas Center for Space Research and that from satellite laser ranging observations. Periodic signals can be seen from the wavelet spectra. A Gaussian smoothing with a radius of 300 km is used in the gravity model-based mass rate estimation. Meanwhile, NASA's Ice, Cloud, and land Elevation Satellite (ICESat) has provided repeated laser altimeter data, and the ice sheet height changes are estimated by using crossover analysis. The mass rates estimated from GRACE are compared to the ice sheet height changes from ICESat. The mass rate in Amundsen Sea Embayment is estimated up to −8 cm/yr from GRACE, while the ice sheet height changes observed from ICESat is up to −32 cm over more than 3 years, this shows the comparable results in this region.

Recent changes in the Earth's oblateness driven by Greenland and Antarctic ice mass loss

[1] We use temporal gravity variations from GRACE to investigate changes in a 34-year time series of Earth's oblateness (J2) observed by satellite laser ranging (SLR). We use 2002–2010 GRACE data to compute the effects of Greenland and Antarctic ice mass variations on J2 (2.0 and 1.7 × 10−11/year respectively). Their combined effect on the J2 trend during the GRACE mission is 3.7 × 10−11/year, which agrees well with the GIA-corrected SLR J2 trend over the same time period. The results suggest that at least since 2002, ice loss from Greenland and Antarctica has been the dominant contributor to the current GIA-corrected J2 trend, which apparently began sometime in the 1990s.

Design considerations for a dedicated gravity recovery satellite mission consisting of two pairs of satellites

Future satellite missions dedicated to measuring time-variable gravity will need to address the concern of temporal aliasing errors; i.e., errors due to high-frequency mass variations. These errors have been shown to be a limiting error source for future missions with improved sensors. One method of reducing them is to fly multiple satellite pairs, thus increasing the sampling frequency of the mission. While one could imagine a system architecture consisting of dozens of satellite pairs, this paper explores the more economically feasible option of optimizing the orbits of two pairs of satellites. While the search space for this problem is infinite by nature, steps have been made to reduce it via proper assumptions regarding some parameters and a large number of numerical simulations exploring appropriate ranges for other parameters. A search space originally consisting of 15 variables is reduced to two variables with the utmost impact on mission performance: the repeat period of both pairs of satellites (shown to be near-optimal when they are equal to each other), as well as the inclination of one of the satellite pairs (the other pair is assumed to be in a polar orbit). To arrive at this conclusion, we assume circular orbits, repeat groundtracks for both pairs of satellites, a 100-km inter-satellite separation distance, and a minimum allowable operational satellite altitude of 290 km based on a projected 10-year mission lifetime. Given the scientific objectives of determining time-variable hydrology, ice mass variations, and ocean bottom pressure signals with higher spatial resolution, we find that an optimal architecture consists of a polar pair of satellites coupled with a pair inclined at 72°, both in 13-day repeating orbits. This architecture provides a 67% reduction in error over one pair of satellites, in addition to reducing the longitudinal striping to such a level that minimal post-processing is required, permitting a substantial increase in the spatial resolution of the gravity field products. It should be emphasized that given different sets of scientific objectives for the mission, or a different minimum allowable satellite altitude, different architectures might be selected.

Satellite gravimetry observation of Antarctic snow accumulation related to ENSO

Interannual ice-mass variations along the Antarctic Peninsula (AP) and in the Amundsen Sea Sector (AS) are obtained for the years 2002 until 2009 using satellite data of the Gravity Recovery and Climate Experiment, that correlate well (r ≈ 0.7) with accumulation variations based on the net precipitation from the European Centre for Medium Range Weather Forecasts. Moreover, mass signals for AP and AS are anti-correlated in time (r ≈ − 0.4) and contain El Niño Southern Oscillation signatures related to the strength of the Amundsen Sea Low pressure system, that has a dominant influence on West Antarctic atmospheric moisture transports. The GRACE interannual mass variations exhibit root-mean squared amplitudes of: 16.4 ± 4.1 Gt (AP) and 28.6 ± 10.5 Gt (AS), which are significant compared to the mean annual mass loss of − 110.2 ± 6.7 Gt/a in coastal West Antarctica.

Climate effects on volcanism: influence on magmatic systems of loading and unloading from ice mass variations, with examples from Iceland

Pressure influences both magma production and the failure of magma chambers. Changes in pressure interact with the local tectonic settings and can affect magmatic activity. Present-day reduction in ice load on subglacial volcanoes due to global warming is modifying pressure conditions in magmatic systems. The large pulse in volcanic production at the end of the last glaciation in Iceland suggests a link between unloading and volcanism, and models of that process can help to evaluate future scenarios. A viscoelastic model of glacio-isostatic adjustment that considers melt generation demonstrates how surface unloading may lead to a pulse in magmatic activity. Iceland's ice caps have been thinning since 1890 and glacial rebound at rates exceeding 20 mm yr(-1) is ongoing. Modelling predicts a significant amount of 'additional' magma generation under Iceland due to ice retreat. The unloading also influences stress conditions in shallow magma chambers, modifying their failure conditions in a manner that depends critically on ice retreat, the shape and depth of magma chambers as well as the compressibility of the magma. An annual cycle of land elevation in Iceland, due to seasonal variation of ice mass, indicates an annual modulation of failure conditions in subglacial magma chambers.

Calculating trends from GRACE in the presence of large changes in continental ice storage and ocean mass

SUMMARY A simulation of monthly global gravity coefficients has been created that represents time-variable hydrology, ice mass loss and global mean sea level rise. Hydrology variations are from a numerical model, whereas the ice mass variations are based on recently observed rates and patterns of melt for glaciers, Greenland and Antarctica. A eustatic sea level variation consistent to balance the mass variations over land is added. This simulation is then used to test the capability of recovering trends in ocean mass, continental water storage and Greenland and Antarctica melting, using methods used to determine these from GRACE data. We find that ocean mass trends can be significantly biased low by the large melting rates from Greenland, Antarctica and glaciers, unless data within 300 km of continents is ignored. Any smoothing of the data beyond a truncation to degree/order 60 will also slightly bias the result. Trends of continental water storage and Antarctica mass loss also tend to be biased due to the sea level rise signal leaking into the estimate. Greenland melting rates are not affected.

Effects of ice-melt induced gravity changes and solid earth deformation in the Netherlands

Determining sea-level change caused by continental ice mass variations is a far more complicated matter than one might think. Even if effects like induced changes in ocean currents or thermal expansion of ocean water are neglected, melt water does not redistribute uniformly and homogeneously over the world’s oceans. If land ice melts, the gravity field of the earth changes due to the redistribution of the ice and melt water masses.

Antarctica seasonal mass variations detected by GRACE

The newly available GRGS-EIGEN-GL04-30day solutions computed by the GRGS group in Toulouse are used to study inter- and intra-annual mass variations in Antarctica. The series of gravity coefficients cover the period from July 2002 to March 2005. They are corrected for ocean tides, ocean high frequencies and atmospheric pressure, so the remaining signal mostly comes from ice mass variations and post-glacial rebound. The errors of these fields are estimated to be less than 2.4 cm of water height equivalent, with punctual values of only 0.5 cm. The polar Antarctica zone benefits from a low error level, which compensates for the weak gravity variations. The temporal signal computed over the whole continent shows a clear seasonal cycle, with a maximum of precipitation during winter months and a minimum during summer months. The ratio between winter and summer snow precipitation is also estimated to be 2.75 which accords well with previous studies. The gravity fields are developed to provide suitable information up to 666 km. The study could therefore focus on regional areas. The coastal zones exhibit higher variable signals with stronger snow accumulation rates than the central part, in agreement with climatologic models and in situ observations. The peninsula zone has the highest values, with a clear semi-annual component.

II: SOLID EARTH PHYSICS: Long Wavelength Sea Level and Solid Surface Perturbations Driven by Polar Ice Mass Variations: Fingerprinting Greenland and Antarctic Ice Sheet Flux

Rapid ice mass variations within the large polar ice sheets lead to distinct and highly non-uniform sea-level changes that have come to be known as ‘sea-level fingerprints’. We explore in detail the physics of these fingerprints by decomposing the total sea-level change into contributions from radial perturbations in the two bounding surfaces: the geoid (or sea surface) and the solid surface. In the case of a melting event, the sea-level fingerprint is characterized by a sea-level fall in the near-field of the ice complex and a gradually increasing sea-level rise (from 0.0 to 1.3 times the eustatic value) as one considers sites at progressively greater distances (up to ≈ 90° or so) from the ice sheet. The far-field redistribution is largely driven by the relaxation of the sea-surface as the gravitational pull of the ablating ice sheet weakens. The near-field sea-level fall is a consequence of both this relaxation and ocean-plus-ice unloading of the solid surface. We argue that the fingerprints provide a natural explanation for geographic variations in sea-level (e.g., tide gauge, satellite) observations. Therefore, they furnish a methodology for extending traditional analyses of these observations to estimate not only the globally averaged sea-level rate but also the individual contributions to this rate (i.e., the sources).

Toward global inverse solutions for current and past ice mass variations: Contribution of secular satellite gravity and topography change measurements

We investigate the accuracy and resolution of estimating global ice mass variations using secular gravity and ice elevation change observations by the planned Gravity Recovery and Climate Experiment (GRACE) and ICESat missions. The gravity and altimetry data combination can determine the total bedrock uplift rate with root‐mean‐square (RMS) errors of 0.2–1.3 mm/yr when Gaussian averaged over a half scale of 250 km. Moreover, covariance analyses indicate that the mean snow compaction error can be constrained to the level of 3 mm/yr in equivalent Antarctic ice thickness change. The mean Antarctic present‐day ice mass change could then be determined to about 4 mm/yr. For a known viscosity profile, such data sets provide a spatial estimate of a linear combination of the late Pleistocene deglaciation and a more recent past trend (last few thousand years) in the Greenland and Antarctica mass balance. For example, when the linear rate of the recent past trend is estimated solely for ice history, the RMS errors of the 450‐km Gaussian averages range between 1 and 3 cm/yr. Although contaminated by the signature of present‐day hydrological variations over the deglaciated areas, the 450‐km Gaussian‐averaged Last Glacial Maximum height of the ancient ice sheets can be determined to a RMS level of 300 m. The mean recovery errors are less than 100 m. However, the gravity/altimeter data cannot resolve the load history and lower mantle viscosity simultaneously. Additional data such as relative sea level records must be invoked to overcome this difficulty.

Carbon dioxide and the ?18O record of late-Quaternary climatic change: a global model

A dynamical model for the late-Quaternary global variations of δ18O, mean ocean surface tempeature τ, ice mass I, deep ocean temperature θ, and atmospheric carbon dioxide concentration μ, is constructed. This model consists of two diagnostic equations (for δ18O and τ), and three prognostic equations (for I, θ, and μ) of a form studied extensively in previous articles. The carbon dioxide equation includes forcing by a representation of the Milankovitch earth-orbital radiation effects, and contains a basic instability that drives a free oscillation of period near 100,000 years. The system is constrained to conserve mass and energy, contain physically plausible feedbacks including a system time constant no greater than 10.000 years, and be robust (i. e., structurally stable in the presence of expected noise levels and uncertainties in values of coefficients). Within the limits of these constraints, coefficients are chosen such that (i) the solution gives a good fit to the observed SPECMAP δ18O variations, and (ii) the ice mass variations are qualitatively similar to the δ18O variations. The predicted long term variations of sea surface temperature and atmospheric carbon dioxide are in reasonably good agreement with the limited observational evidence available for these quantities, while the predicted variations of deep ocean temperature remain to be verified when paleoclimatic estimates of this quantity become available. The relative contributions of ice mass changes and surface water temperature changes to the variations of δ18O at any time are given by the model.