Table 1. Summary of observations used in this study
LSWTMODIS (1 km2)70 pixels (41 lakes)2010.11.01–2012.05.31Objective analysisLSWTAATSR (1 km2)15 pixels (Lake Ladoga)April 2011Objective analysisLSWTFMI Marine ServicesaSwedish lakesa,bOct.–May, 2010–2012Objective analysisLake water temperatureSYKE measured27 Finnish lakes2010.11.01–2012.05.31Objective analysisFreeze-up/break-up datesSYKE visual observation27 Finnish lakes2010.11.01–2012.05.31EvaluationIce fractionMERIS (300 m2)Lake LadogaApril 2011Evaluation
Fig. 1
(a) Location of the MODIS pixels over the northern lakes. Independent lakes are marked with orange dots. (b) Location of 27 lakes (dark blue polygons) with SYKE measurement sites in Finland. (c) Detailed view of the selected MODIS and AATSR pixels over the lakes Ladoga (left) and Onega (right).
Table 2. Definition of the HIRLAM experiments
TRULAK2010.11.01–2012.05.31SYKEaFLake+6 hcNHFLAK2010.11.01–2012.05.31SYKEa+MODISbFLake+6 hcNHALAK2012.01.01–2012.05.31SYKEa+MODISbprevious analysisNHFLAA2011.04.01–2011.04.30SYKEa+AATSRdFLake+6 hcNHALAA2011.04.01–2011.04.30SYKEa+AATSRdPrevious analysis
Table 3. Freezing and melting dates of selected lakes given by observations (SYKE and MODIS) and analyses by experiments (TRULAK, NHALAK, NHFLAK as defined in Table 2)
Lappajärvi, Finland23.67E 63.14NMean depth 7 m SYKE2010050420101122201105032011123120120502 MODIS2010050520101105201105012011120320120429 TRULAK–20101108201104182011121720120424 NHFLAK–20101117201104212011121320120424 NHALAK––––20120429Inari, Finland28.10E 68.87NMean depth 14 m SYKE2010060320101126201106032011123020120531 MODIS2010051220101106201105152011120120120527 TRULAK–Before 20101101201105062011112120120509 NHFLAK–20101107201105072011112520120507 NHALAK––––20120526Ladoga,a Russia32.50E 60.82NMean depth 33 m MODIS2010051320110115201105082012012520120501 MERIS––20110509–– TRULAK–20101206–2011011120110404–162012012320120401–13 NHFLAK–20101213–20110101201104302012012720120428 NHALAK–––2012012820120511Vänern,b Sweden13.75E 59.15NMean depth 50 m MODIS201004102011020620110409–0429Partial icePartial ice TRULAK–2010110820110410–0430Almost no iceAlmost no ice NHFLAK–2010122320110412Almost no iceAlmost no ice NHALAK–––Almost no iceAlmost no iceBolmen, Sweden13.69E 56.87NMean depth 5 m MODIS2010040920101130201103282012011520120223 TRULAK–20101127201103202012012320120312 NHFLAK–20101127201103212012012320120312 NHALAK–––2012020620120226Hjälmaren, Sweden15.85E 59.24NMean depth 10 m MODIS2010041820101121201104142011010820120326 TRULAK–20101108–12022011040820120108–013020120316 NHFLAK–20101128201104042012011920120325 NHALAK–––2012020320120329Kuito, Russia31.42E 65.14NMean depth 19 m MODIS2010051420101115201105192011112120120513 TRULAK–20101105201104252011112920120417 NHFLAK–201011082011042720111122–2920120417 NHALAK––––20120516Valday, Russia33.31E 57.99NMean depth 14 m MODIS2010050720101122201005082011112220120412 TRULAK–20101127201104032011122520120327 NHFLAK–20101202201104042011122520120329 NHALAK––––20120420
[i] aLadoga, pixel 9, see Fig. 1 for map.
Fig. 2
Surface temperature on 12 April 2011: (a) MODIS visible image, (b) MERIS ice fraction, (c) AATSR surface temperature (between 8 and 10 AM local time), (d) MODIS daytime surface temperature (between 10 AM and 12 PM local time) and (e) MODIS nighttime (between 10 PM and 3 AM local time).
Fig. 3
HIRLAM ice fraction (0–1) on 12 April 2011, diagnosed from LSWT: (a) analysis, (b) background and (c) their differences. NHFLAK (SYKE, FLake, MODIS) at 00 UTC (upper panel) and at 12 UTC (middle panel), and NHFLAA (SYKE, MODIS) at 06 UTC (lower panel).
Fig. 4
LSWT observations used for HIRLAM analysis over Lake Ladoga on 12 April 2011: (a) MODIS for NHFLAK (SYKE, FLake, MODIS) at 00 UTC, (b) MODIS for NHFLAK at 12 UTC and (c) AATSR for NHFLAA (SYKE, FLake, AATSR) at 06 UTC.
Fig. 5
Analysis (red), background (black) and observation (blue) in the grid point nearest to pixel 7 over central Ladoga during April 2011 in the experiments (a) NHFLAA (SYKE, FLake, AATSR), (b) NHFLAK (SYKE, FLake, MODIS), (c) NHALAA (SYKE, AATSR) and (d) NHALAK (SYKE, MODIS). Only times when MODIS observations were available are shown. No data are rejected here.
Fig. 6
Same as in Fig. 5 but over Lake Lappajärvi (15 March – 31 May 2012) in the experiments (a) NHALAK (SYKE, MODIS) and (b) NHFLAK (SYKE, FLake, MODIS) for the selected MODIS pixel (23.70 E, 63.22 N), (c) NHALAK (SYKE, MODIS) and (d) NHFLAK (SYKE, FLake, MODIS) for the SYKE measurement point (23.67 E, 63.15 N).
Fig. 7
MODIS-Aqua visible images over Lake Lappajärvi on 25 April (left, 8:30–12:10 UTC) and 1 May (right, 9:50–11:30 UTC), 2012.
Fig. 8
Comparison of LSWT derived by MODIS with LSWT analysed by experiments NHFLAK (SYKE, FLake, MODIS), NHALAK (SYKE, MODIS) and TRULAK (SYKE, FLake) for (a) Lake Valday and (b) Lake Kuito.