Today's noaa19 overpass of Greenland at 1436z gave minimum surface temperature of -72.1C near 72.3N 37.9W, about one degree down on yesterday's values in mid afternoon and late evening, the latter sampled by the metop-a satellite, confirming the noaa19 value earlier in the day.
Further to yesterday's discussion on USW, the channel used for these measurements is the 11 micrometres IR channel 4. I think that the calibration data for the IR sensor is transmitted by the satellite along with the sensed data. I also think that these AVHRR instruments are capable of onboard calibration, so I would not expect to see much error in these measurements, especially as the principal source of error is contamination of the upwelling radiation by intervening cloud, which is absent over Greenland at the moment.
> Today's noaa19 overpass of Greenland at 1436z gave minimum surface > temperature of -72.1C near 72.3N 37.9W, about one degree down on > yesterday's values in mid afternoon and late evening, the latter sampled > by the metop-a satellite, confirming the noaa19 value earlier in the day.
> Further to yesterday's discussion on USW, the channel used for these > measurements is the 11 micrometres IR channel 4. I think that the > calibration data for the IR sensor is transmitted by the satellite along > with the sensed data. I also think that these AVHRR instruments are > capable of onboard calibration, so I would not expect to see much error in > these measurements, especially as the principal source of error is > contamination of the upwelling radiation by intervening cloud, which is > absent over Greenland at the moment.
Thanks Bernard, this is really most interesting. A student of mine many years ago presented a student lecture on the climate of Greenland (mainly coastal, but a bit of the plateau). I do not have the notes but IIRC these temperature values are very low for the time of year, exceptionally low? Not sure. Anyone?
If they are exceptional then it will have an affect on our weather, not directly of course, but synoptically.
> > Today's noaa19 overpass of Greenland at 1436z gave minimum surface
> > temperature of -72.1C near 72.3N 37.9W, about one degree down on
> > yesterday's values in mid afternoon and late evening, the latter sampled
> > by the metop-a satellite, confirming the noaa19 value earlier in the day.
> > Further to yesterday's discussion on USW, the channel used for these
> > measurements is the 11 micrometres IR channel 4. I think that the
> > calibration data for the IR sensor is transmitted by the satellite along
> > with the sensed data. I also think that these AVHRR instruments are
> > capable of onboard calibration, so I would not expect to see much error in
> > these measurements, especially as the principal source of error is
> > contamination of the upwelling radiation by intervening cloud, which is
> > absent over Greenland at the moment.
> Thanks Bernard, this is really most interesting. A student of mine many
> years ago presented a student lecture on the climate of Greenland (mainly
> coastal, but a bit of the plateau). I do not have the notes but IIRC these
> temperature values are very low for the time of year, exceptionally low? Not
> sure. Anyone?
> If they are exceptional then it will have an affect on our weather, not
> directly of course, but synoptically.
> > Today's noaa19 overpass of Greenland at 1436z gave minimum surface
> > temperature of -72.1C near 72.3N 37.9W, about one degree down on
> > yesterday's values in mid afternoon and late evening, the latter sampled
> > by the metop-a satellite, confirming the noaa19 value earlier in the > > day.
> > Further to yesterday's discussion on USW, the channel used for these
> > measurements is the 11 micrometres IR channel 4. I think that the
> > calibration data for the IR sensor is transmitted by the satellite along
> > with the sensed data. I also think that these AVHRR instruments are
> > capable of onboard calibration, so I would not expect to see much error > > in
> > these measurements, especially as the principal source of error is
> > contamination of the upwelling radiation by intervening cloud, which is
> > absent over Greenland at the moment.
> Thanks Bernard, this is really most interesting. A student of mine many
> years ago presented a student lecture on the climate of Greenland (mainly
> coastal, but a bit of the plateau). I do not have the notes but IIRC these
> temperature values are very low for the time of year, exceptionally low? > Not
> sure. Anyone?
> If they are exceptional then it will have an affect on our weather, not
> directly of course, but synoptically.
I didn't point this out before, but the temperature measured by the satellite sensor is the ice surface value, and as we are all aware from grass minimum thermometers over snow, the surface temperature can easily be 8C to 10C lower than the air temperature.
> > > Today's noaa19 overpass of Greenland at 1436z gave minimum surface
> > > temperature of -72.1C near 72.3N 37.9W, about one degree down on
> > > yesterday's values in mid afternoon and late evening, the latter sampled
> > > by the metop-a satellite, confirming the noaa19 value earlier in the
> > > day.
> > > Further to yesterday's discussion on USW, the channel used for these
> > > measurements is the 11 micrometres IR channel 4. I think that the
> > > calibration data for the IR sensor is transmitted by the satellite along
> > > with the sensed data. I also think that these AVHRR instruments are
> > > capable of onboard calibration, so I would not expect to see much error
> > > in
> > > these measurements, especially as the principal source of error is
> > > contamination of the upwelling radiation by intervening cloud, which is
> > > absent over Greenland at the moment.
> > Thanks Bernard, this is really most interesting. A student of mine many
> > years ago presented a student lecture on the climate of Greenland (mainly
> > coastal, but a bit of the plateau). I do not have the notes but IIRC these
> > temperature values are very low for the time of year, exceptionally low?
> > Not
> > sure. Anyone?
> > If they are exceptional then it will have an affect on our weather, not
> > directly of course, but synoptically.
> I didn't point this out before, but the temperature measured by the
> satellite sensor is the ice surface value, and as we are all aware from
> grass minimum thermometers over snow, the surface temperature can easily be
> 8C to 10C lower than the air temperature.
Ah, I have been puzzling the stability of Antarctica's system, coupled
with the heights involved at surface level there, it explains a lot.
