07 March, 2015

Experiment and Result: How Salinity Affects Sea Surface Temperature

When you know you're in a devastating drought, what's the last type of weather forecast you'd ever want to hear when watching TV? If that drought is in the Midwest, it would be Chinook winds, would it not? In California, of course, which is already in its worst drought in 1200 years, that worst possible forecast would of course be the hellish Santa Ana winds. Yet those winds were exactly what were forecasted yesterday. Despite the fact that the subtropical jet is intensifying again and EPO is going positive, California was still not getting in on the action. So, I decided it was time to investigate, figure out what was going on, and take action to counter that myself.

For starters, I have seen some rather interesting photos of people floating on the surface of the Dead Sea without any flotation devices due to how dense that water is, and with explanations that the density is in turn due to the salinity. Also, I am fully aware that a combination of temperature and salinity, with salinity being by far on top, is what drives the thermohaline circulation, since warm water with dry air on top of it (which can be either hot/dry or cold/dry and still have the same effect) tends to evaporate faster, and since evaporation leaves all the salt behind, the water that is left behind becomes saltier, denser, and thus, more prone to downwelling.

Therefore, I thought of a rather ingenious hypothesis the night before (worship/post-worship fun night): What would happen to the sea surface temperatures off SoCal if the salinity of the local waters were to suddenly increase during a critical time when hot, dry air is blowing over those waters in the form of Santa Ana winds?

Early the following morning, the day those dry Santa Ana winds were forecast, I decided that it was the perfect opportunity to test that hypothesis. I biked to the beach (specifically Salt Creek Beach in Dana Point) to beat the heat, of course, but I also made a little pit stop on the way there. In Laguna Niguel, practically right on my route there, is a Walmart. I stopped there to see how expensive those one-liter cans of salt were. Sure enough, they cost only 78¢ per can. So, I got four of them, totaling 1 full gallon of pure salt, enough to double the salinity of 33.3 gallons of seawater. Then, I slipped that salt in my backpack, headed down to the beach, spotted a rip current, and dumped all that salt in the water at about 9AM, which is by far the perfect time on a day like that since it gives that increased salt time to force some of the local waters to downwell (and evaporate) prior to those hellish Santa Ana conditions.

From there, I rode back up to Laguna Niguel to have lunch, then went back to the beach, this time to Aliso Beach. When I got there, I got in the water, and noticed that its temperature had indeed risen. And when those (weak) Santa Ana winds then began blowing, the water didn't cool as it normally would have. No, because of the increased local salinity, it actually warmed due to the resulting feedback effect. Remember, when air is dry, water evaporates VERY rapidly. And when salt water evaporates, the vapor becomes fresh water, leaving the salt behind, making the water saltier and denser still. Since water that is dense becomes heavy and wants to downwell, that downwelling pulls heat down with it, making the water even warmer.

I then checked the sea surface temperature map this morning. When I had last checked it prior to that intervention ― sure enough, just before heading down to the beach ― it was indeed anomalously warm, but only in about the low 60's. This morning, however, this tongue of warm water in the upper 60's to low 70's (!) that didn't exist before suddenly stretched from Baja up the coast almost to Los Angeles. Then, as I zoomed out even further, I noticed an almost dead Kuroshio Current with exceptionally cold water choking it out, and also noticed more anomalous equatorial downwelling east of the Date Line, not to mention eastward movement of Asian water against the will of the Trade Winds (the calling card of El NiƱo).

I was stunned. How could I have known that busting this devastating drought would be that easy? Remember, water that comes in to replace that resulting anomalous downwelling naturally wants to curve to the right due to the Coriolis effect. That means from Mexico, around the tip of Baja, and ultimately northward. Consequently, warm water must also then flow eastward along the equator (which already has a level that is rather imbalanced) to replace THAT water, and so on and so forth. The results I spotted on that map matched perfectly with my hypothesis.

SST anomalies of that scale right off California may result in dry winters, to be fair, but when it comes to summer (read: hurricane season), they couldn't be more beneficial, to say the least. They not only enhance the hurricane season in the eastern Pacific but also the monsoon, which tends to cause a normally dry season to become a season of pop-up convective thunderstorms and dew points in the 70's. What's more, if the resulting SSTs reach a certain threshold (like they did in 2006, when a buoy stationed near Newport Beach reported 80-degree waters and another one further offshore in San Diego County reported SSTs near 83°F) ― 82.8°F ― they end up becoming fuel for tropical cyclones.

Last summer, Hurricane Marie was a storm for the record books, to say the least. It was the first tropical cyclone to reach Category 5 status in the Pacific east of the International Date Line (the dividing line between typhoons and hurricanes) since 2010's Hurricane Celia. Despite not even coming close to California shores and weakening to a tropical storm at the same latitude as Ensenada due to the exceptionally cold waters that normally serve to shield us Californians from hurricanes (that's exactly why you don't usually hear of hurricanes hitting California: cold water), Marie's 160mph sustained winds with 195mph gusts extending a whopping 400 miles out from the eye were enough to send 25-foot waves careening into the California coast from more than 1000 miles away. Surfers, of course, were absolutely loving it, but they were the only ones who were. Those who lived near the coast, especially low-lying regions such as Seal Beach, woke up to find several feet of salt water in their homes, and a lifeguard station up in Malibu was completely washed away into the ocean.

Should a storm like Marie actually take advantage of anomalous sea surface temperatures and make landfall in California at the perfect time, however, it would definitely be the ultimate drought-buster, to be sure. Then again, it's kind of a two-edged sword due to the amount of wind and (especially) flood damage that hurricanes cause, but it would definitely be a sure way to get those reservoirs full and our groundwater up to par. Then again, that's a topic for another post that won't be published until it actually occurs...