Editing GRACE and GRACE-FO (section)

=== Oceanography, hydrology, and ice sheets ===
GRACE chiefly detected changes in the distribution of water across the planet. Scientists use GRACE data to estimate ocean bottom pressure (the combined weight of the ocean waters and atmosphere), which is as important to oceanographers as [[atmospheric pressure]] is to meteorologists.<ref name="nasa20151101">{{cite web |url=https://grace.jpl.nasa.gov/news/77/nasa-finds-new-way-to-track-ocean-currents-from-space/ |title=NASA Finds New Way to Track Ocean Currents from Space |publisher=NASA/Jet Propulsion Laboratory |first=Carol |last=Rasmussen |date=1 November 2015 |access-date=14 March 2018}}</ref> For example, measuring ocean pressure gradients allows scientists to estimate monthly changes in deep ocean currents.<ref>{{cite web |url=https://www.nasa.gov/audience/foreducators/k-4/features/F_Measuring_Gravity_With_Grace.html |title=Measuring Gravity With GRACE |publisher=NASA |first=Dan |last=Stillman |date=16 April 2007 |access-date=14 March 2018}}</ref> The limited resolution of GRACE is acceptable in this research because large ocean currents can also be estimated and verified by an ocean buoy network.<ref name="nasa20151101" /> Scientists have also detailed improved methods for using GRACE data to describe Earth's gravity field.<ref>{{cite journal |title=Improved methods for observing Earth's time variable mass distribution with GRACE using spherical cap mascons |journal=Journal of Geophysical Research: Solid Earth |first1=Michael M. |last1=Watkins |first2=David N. |last2=Weise |first3=Dah-Ning |last3=Yuan |first4=Carmen |last4=Boening |first5=Felix W. |last5=Landerer |display-authors=1 |volume=120 |issue=4 |pages=2648–2671 |date=April 2015 |doi=10.1002/2014JB011547 |bibcode=2015JGRB..120.2648W|doi-access=free }}</ref> GRACE data are critical in helping to determine the cause of [[sea level rise]], whether it is the result of mass being added to the ocean – from melting [[glacier]]s, for example – or from [[thermal expansion]] of warming water or changes in [[salinity]].<ref>{{cite web |url=http://www.jpl.nasa.gov/news/news.php?feature=1112 |title=NASA Missions Help Dissect Sea Level Rise |publisher=NASA/Jet Propulsion Laboratory |first=Rosemary |last=Sullivant |date=14 June 2006 |access-date=14 March 2018}}</ref>  High-resolution static gravity fields estimated from GRACE data have helped improve the understanding of global [[ocean current|ocean circulation]]. The hills and valleys in the ocean's surface ([[ocean surface topography]]) are due to currents and variations in Earth's gravity field. GRACE enables separation of those two effects to better measure ocean currents and their effect on climate.<ref name="oceanography">{{cite web |url=https://climate.nasa.gov/news/152/gravity-data-sheds-new-light-on-ocean-climate/ |title=Gravity data sheds new light on ocean, climate |publisher=NASA |first=Rosemary |last=Sullivant |date=26 August 2009 |access-date=14 March 2018}}</ref>

GRACE data have provided a record of mass loss within the [[ice sheet]]s of Greenland and Antarctica.  Greenland has been found to lose {{val|280|58|ul=Gt}} of ice per year between 2003 and 2013, while Antarctica has lost {{val|67|44|ul=Gt}} per year in the same period.<ref name="Velicogna et al. (2014)">{{cite journal |last1=Velicogna |first1=Isabella |author-link=Isabella Velicogna|last2=Sutterly |first2=T.C. |last3=van den Broeke |first3=M.R. |title=Regional acceleration in ice mass loss from Greenland and Antarctica using GRACE time-variable gravity data |journal=J. Geophys. Res. Space Phys. |date=2014 |issue=119 |pages=8130–8137 |doi=10.1002/2014GL061052 |bibcode=2014GeoRL..41.8130V |volume=41 |hdl=1874/308354 |s2cid=53062626 |hdl-access=free}}</ref> These equate to a total of 0.9&nbsp;mm/yr of sea level rise.  Increases in [[ocean heat content]] resulting from [[Earth's Energy Imbalance]] of about 0.8&nbsp;W/m<sup>2</sup> were similarly found spanning 2002 thru 2019.<ref>{{cite journal |last1=Marti |first1=Florence |last2=Blazquez |first2=Alejandro |last3=Meyssignac |first3=Benoit |last4=Ablain |first4=Michaël |last5=Barnoud |first5=Anne |last6=Fraudeau |first6=Robin |last7=Jugier |first7=Rémi |last8=Chenal |first8=Jonathan |last9=Larnicol |first9=Gilles |last10=Pfeffer |first10=Julia |last11=Restano |first11=Marco |last12=Benveniste |first12=Jérôme |display-authors=5 |title=Monitoring the ocean heat content change and the Earth energy imbalance from space altimetry and space gravimetry |journal=Earth System Science Data |year=2021 |doi=10.5194/essd-2021-220 |doi-access=free}}</ref><ref>{{cite journal |last1=Hakuba |first1=M.Z. |last2=Frederikse |first2=T. |last3=Landerer |first3=F.W. |title=Earth's Energy Imbalance From the Ocean Perspective (2005–2019) |journal=Geophysical Research Letters |volume=48 |issue=16 |date=28 August 2021 |doi=10.1029/2021GL093624 |doi-access=free|bibcode=2021GeoRL..4893624H }}</ref>  

GRACE data have also provided insights into regional hydrology inaccessible to other forms of remote sensing: for example, [[overdrafting|groundwater depletion]] in India<ref>{{cite journal |last1=Tiwari |first1=V.M. |last2=Wahr |first2=J. |author-link2=John M. Wahr |last3=Swenson |first3=S. |title=Dwindling groundwater resources in northern India, from satellite gravity observations |journal=Geophysical Research Letters |date=2009 |volume=36 |issue=18 |at=L18401 |doi=10.1029/2009GL039401 |bibcode=2009GeoRL..3618401T|doi-access= }}</ref> and California.<ref name="Famiglietti et al. (2011)">{{cite journal |last1=Famiglietti |first1=J |title=Satellites measure recent rates of groundwater depletion in California's Central Valley |journal=Geophys. Res. Lett. |date=2011 |volume=38 |issue=3 |at=L03403 |doi=10.1029/2010GL046442 |bibcode=2011GeoRL..38.3403F |url=https://escholarship.org/content/qt8g651992/qt8g651992.pdf?t=n0u8a0|doi-access=free }}</ref>  The annual hydrology of the [[Amazon basin]] provides an especially strong signal when viewed by GRACE.<ref name="Tapley et al. (2004)">{{cite journal |last1=Tapley |first1=Byron D. |last2=Bettadpur |first2=Srinivas |last3=Ries |first3=John C. |last4=Thompson |first4=Paul F. |last5=Watkins |first5=Michael M. |title=GRACE Measurements of Mass Variability in the Earth System |journal=Science |date=2004 |volume=305 |issue=5683 |pages=503–505 |doi=10.1126/science.1099192 |bibcode=2004Sci...305..503T |pmid=15273390 |s2cid=7357519 |url=https://authors.library.caltech.edu/52043/7/Tapley.SOM.pdf}}</ref>  A [[University of California, Irvine]]-led study published in ''[[Water Resources Research]]'' on 16 June 2015 used GRACE data between 2003 and 2013 to conclude that 21 of the world's 37 largest aquifers "have exceeded sustainability tipping points and are being depleted" and thirteen of them are "considered significantly distressed." The most over-stressed is the [[Arabian Aquifer System]], upon which more than 60 million people depend for water.<ref name="NASA_GRACE">{{cite web |url=http://www.jpl.nasa.gov/news/news.php?feature=4626 |title=Study: Third of Big Groundwater Basins in Distress |publisher=NASA |date=16 June 2015 |access-date=26 June 2015}}</ref>