Days getting longer, more sun energy coming in

Those new to the blog may not have seen my “geochron” style maps of daylight on earth like the one above. They basically show where on earth there is daylight, at a given time and date. They are seen often in movies (“The Hunt for Red October” and other Clancy, “Three Days of the Condor”) and in some TV shows (“NCIS”). The key thing to notice above is that now we are into Spring and the sun is north of the equator, most of the sunlight is now in the Northern Hemisphere! Notice that the days are a little longer right now in Arctic regions than at the equator…that difference will change as the sun’s position moves north in April, May, and most of June. The sun will also spread out over more of the Northern Hemisphere, meaning our days will get longer.

You can see that, as shown on the “geochron” image, the sun is fairly evenly distributed north-to-south right now, only slightly concentrated in the N. Hemisphere on the satellite loop below, showing visible satellite pictures as the sun rose over the Atlantic and eastern US this morning.

As I mentioned earlier, our days are getting longer. Below is a plot of the length of daylight in Birmingham by day of year. Below it is the change in daylight per day (for math geeks like me, the derivative of the top graph, since the top one is basically -cosine, the second one is sine).

We are gaining about 2 minutes of daylight per day right now. Due to the longer days and the higher sun angle, the amount of solar energy coming in every day is increasing rapidly, also. Back on Dec 21, 4.81 kilowatt hours (per square meter of ground surface) of sun energy were coming in every day (assuming full sunshine). Today, 9.26 kWh will come in, and by June 21, 11.92 kWh will come in. However, we have already almost doubled the sun energy coming in every day, partially explaining why it is warming up, and even when cold air comes in, it can’t last as long because the sun heats it up so fast.

As James points out below, we can still have a freeze, or especially a frost, before the spring is over. One cold front could make it through and drop our temperatures briefly into the upper 20s and lower 30s sometime in the next 2 or 3 weeks. But, the likelihood for freezing temperatures after April 20 is very low.

Category: Met 101/Weather History