Daylight returns to Alaska

March 14th, 2008 |

AKmovie.gif
The visible image comparison shown above includes two images centered on Fairbanks AK (the green box in the center). The images are from the same time — 1730 UTC — one is from 14 March, and one is from 4 March, 11 days earlier. Sunrises [and daylight duration] at Barrow (yellow box), Fairbanks and Anchorage (red box) on 4 March were 17:41 [9 h, 56 m], 16:48 [10 h, 32 m], and 16:49 UTC [10 h, 45 m]. Eleven days later, sunrises [and daylight duration] were 16:52 [11 h, 31 m], 16:11 [11 h, 39 m] and 16:18 [11 h, 43m]. Thus the length of day increased by 95, 67 and 58 minutes, respectively, in those 11 days.

More daylight over northern North America has important consequences. When incoming radiation can exceed outgoing radiation — an event far more likely when the Sun is up — the land will not cool down. It is increasingly difficult to generate cold air over North America as the days lengthen, and at this time of year, the speed at which the days lengthen over Alaska approaches 10 minutes daily.

The later of the two images, shown here, is of a particularly clear day over southern Alaska, and the rugged terrain of both the Alaska Range and the Brooks Range is apparent. Denali, or Mt. McKinley, is visible just to the left of a line connecting Anchorage and Barrow.

White Sands, New Mexico: a source of blowing…sand

March 14th, 2008 |

GOES-12 visible images (Animated GIF)

The large (275 square mile) White Sands National Monument is an very familiar landmark on satellite imagery — the world’s largest surface deposit of gypsum sand stands out as a prominent white feature against the surrounding mountains and valleys of southern New Mexico. Strong winds across that region on 14 March 2008 (gusts as high as 66 mph were reported at Ruidoso) created a plume of blowing sand whose obvious source was White Sands. An animation of GOES-12 visible images (above) shows the development of the plume during the 17:45 – 22:45 UTC (11:45 AM – 4:45 PM local time) period.

MODIS true color image (Google Earth)

A 250-meter resolution Aqua MODIS true color image from the SSEC MODIS Today site (viewed using Google Earth, above) shows greater detail of the plume at around 19:20 UTC (1:20 PM local time). The surface visibility at Alamogordo, New Mexico (station identifier KALM, located about 20 mi or 37 km east of White Sands National Monument) was reduced to 2 miles during the late morning hours on 14 March, as winds increased and gusted to 44 mph.

NOAA ARL forward trajectories

So where did this airborne dust/sand go? NOAA ARL HYSPLIT forward trajectories (above) suggest that lower-tropospheric air parcels originating over the White Sands area at 21:00 UTC on 14 March were transported eastward and then southeastward, reaching the extreme northwestern portion of the Gulf of Mexico on 15 March. Did some of this dust then get entrained into the circulation of a undular bore that moved southward across the Gulf of Mexico on 15 March?