ABSTRACT.A simpl e mi crowave-emlSSlOn m odel is used to simul a te 37 GHz brightn ess tempera tures associa ted with snow pack-melt co nditio ns for locati ons ac ross th e Greenl a nd ice sheet. Th e simulated va lu es a re utilized as threshold valu es a nd co mpa red to d a il y, gridd ed SMMR and SSM / I passive-microwa ve d a ta, in ord er to reveal reg ion .. experiencing melt. The spa ti a l ex tent of th e a rea cl ass ifi ed as melting is exa mined o n a daily, monthl y a nd seasona l (M ay-August) basis for 1979 9 1. Th e typical seaso na l cycle of melt coverage shows melt beginning in la te April , a ra pid in crease in the melting a rea from mid-May to mid-Jul y, a r a pid dec rease in m elt ex tent from la te Jul y throug h mid-August, a nd cessation of melt in late September. Seaso nal ave r ages of th e d a il y melt extents demonstrate an a ppa rent increase in melt coverage ove r th e 13 year peri od of approxim a tely 3.8 % a nnu a ll y (signili ca nt a t th e 95% confid en ce interval). This in crease is d o min a ted by sta tisti call y sig nifi ca nt positi ve tre nds in melt coverage during Jul y a nd August in th e west a nd so uthwe t of the ice shee t. 'V e lind th a t a lin ea r co rrela ti on be twee n microwa\'e-d eri ved melt ex te nt a nd a surface meas ure of a bl a ti o n ra te is sig nili cant inJun e a nd Jul y but not Au g ust, so ca ution mu. t be exercised in usin g th e mi crowave-d erived melt extents in Au g ust. Nevertheless, kn owledge of th e va ri a bility of snow pack melt on th e Gree nla nd ice shee t a deri ved from mi crowave d a ta should prove usc ful in dctecting clim a te cha nge in th e Arctic and exa mining the impac t of clim a te ch a nge on th e ice shee t.

We present a homogenized Greenland blocking index (GBI) daily record from 1851 to 2015, therefore significantly extending our previously published monthly/seasonal GBI analysis. This new time series is analysed for evidence of changes in extreme events, and we investigate the underlying thermodynamic and dynamic precursors. We compare occurrences and changes in extreme events between our GBI record and a recently published, temporally similar daily North Atlantic Oscillation (NAO) series, and use this comparison to test dynamic meteorology hypotheses relating negative NAO to Greenland blocking. We also compare daily GBI changes and extreme events with long‐running indices of England and Wales temperature and precipitation, to assess potential downstream effects of Greenland blocking on UK extreme weather events and climate change. In this extended analysis we show that there have been sustained periods of positive GBI during 1870–1900 and from the late 1990s to present. A clustering of extreme high GBI events since 2000 is not consistently reflected by a similar grouping of extreme low NAO events. Case studies of North Atlantic atmospheric circulation changes linked with extreme high and low daily GBI episodes are used to shed light on potential linkages between Greenland blocking and jet‐stream changes. Particularly noteworthy is a clustering of extreme high GBI events during mid‐October in 4 out of 5 years during 2002–2006, which we investigate from both cryospheric and dynamic meteorology perspectives. Supporting evidence suggests that these autumn extreme GBI episodes may have been influenced by regional sea‐ice anomalies off west Greenland but were probably largely forced by increases in Rossby‐wave train activity originating from the tropical Pacific. However, more generally our results indicate that high GBI winter anomalies are co‐located with sea‐ice anomalies, while there seems to be minimal influence of sea‐ice anomalies on the recent significant increase in summer GBI.

Editor’s note: For easy download the posted pdf of the State of the Climate for 2019 is a low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.

We provide an updated analysis of instrumental Greenland monthly temperature data to 2019, focusing mainly on coastal stations but also analysing icesheet records from Swiss Camp and Summit. Significant summer (winter) coastal warming of $1.7 (4.4) C occurred from 1991-2019, but since 2001 overall temperature trends are generally flat and insignificant due to a cooling pattern over the last 6-7 years. Inland and coastal stations show broadly similar temperature trends for summer. Greenland temperature changes are more strongly correlated with Greenland Blocking than with North Atlantic Oscillation changes. In quantifying the association between Greenland coastal temperatures and Greenland Ice Sheet (GrIS) mass-balance changes, we show a stronger link of temperatures with total mass balance rather than surface mass balance. Based on Greenland coastal temperatures and modelled mass balance for the 1972-2018 period, each 1 C of summer warming corresponds to $(91) 116 GtÁyr −1 of GrIS (surface) mass loss and a 26 GtÁyr −1 increase in solid ice discharge. Given an estimated 4.0-6.6 C of further Greenland summer warming according to the regional model MAR projections run under CMIP6

Editor’s note: For easy download the posted pdf of the State of the Climate for 2017 is a low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.