For the millions of residents living within the Sacramento valley and surrounding areas, extreme summer heat with temperatures soaring above one hundred degrees is about as natural and native as the valley, interior live, and blue oaks that dot the foothills and the Sacramento valley floor. Though, something not so native or natural has managed to creep its way into the valley in the past century, growing and thriving in the heat just as the oaks do, but only proving harmful to residents. That unnatural thing is the haze that envelops Sacramento during those hot days: photochemical smog and ground-level ozone. Brown and grey, shrouding the valley in a toxic bubble, this invasive element has become so pervasive that Sacramento currently ranks within the top ten cities in the United States for the worst ozone pollution and within the top fifteen for short-term particle pollution. So what conditions in Sacramento are so prevalent as to cause this pollution?
As seen in a previous article regarding Sacramento’s pollution, the northern California topography plays a huge role in advancing Sacramento into the top ten cities for the worst air pollution. Though, what initiates the presence of this pollution in the first place is the abundance of nitrogen oxides within the atmosphere, churned out by the 1.3 million-plus cars registered in Sacramento county. With such a massive amount of cars concentrated in densely-populated, urban environment, thousands of tons of pollutants are dumped into the surrounding atmosphere each day, the primary being nitrogen oxide and dioxide which are produced as a result of the burning of fossil fuels. As ultraviolet sunlight reacts with these molecules, they are split apart, forming the constituents of photochemical smog such as ozone, aldehydes, and peroxyacetyl nitrates (PANS). Additionally, the dry, relatively arid climate of the Sacramento valley only further fuels this production as it provides a perfect breeding ground for ultraviolet light reactions with little water vapor to impede the pollution production.
As Sacramento continues to grow in population, the number of vehicles within the county may be expected to increase as well, leading to further pollution from photochemical smog and ground-level ozone. With more fossil fuel run engines belching out nitrogen oxides, pollution will only continue and likely compound, thus producing unhealthy air for the millions that reside within the county. Although photochemical smog and ground-level ozone are the main culprits of this haze and unhealthy air quality, other factors and secondary pollutants contribute to this as well, such as dust particulates stirred into the air from the vast agricultural fields that span the entire valley. As farmers begin to plow and till soil in preparation for planting, billows of dust are seen whirling across the fields and highways before seemingly disappearing through the means of a dust devil, contributing to the haze. Additionally, ash and PM 2.5 from California’s nearly-annual wildfires also help contribute to this haze, smoking out and infiltrating the skies as vegetation dries out and temperatures soar.
Although a common factor in the day to day life of Sacramentans, haze and pollution are not something that should at all be considered native and here to stay. Instead, it is a current, very serious problem, but one that the California Air Resources Board (CARB) and other agencies work diligently to battle. “Spare the Air” day warnings are a common tool used by this agency, encouraging residents to reduce their need for transportation or fossil fuel burning engines by taking public transit or ride-sharing. No-burn days are also issued, prohibiting citizens from burning any sort of fire in an effort to combat ash and PM 2.5 in the local atmosphere. Through these efforts and the cooperation and education of citizens, Sacramento haze may one day be a thing of the past, permitting unimpeded grand views of the oak-dotted foothills, the golden coastal mountains, and the snow-capped Sierra Nevadas once again.
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© 2019 Weather Forecaster Alexis Clouser
DISCUSSION: On the week of July 15, A massive humid heatwave struck much of the Central United States from Kansas and Oklahoma to Ohio and West Virginia. The heatwave started after the remnants of Hurricane Barry was absorbed by a trough of low pressure that came from Canada. After the trough moved out towards New York and the East Coast, a strong ridge of high pressure built over the area which cleared the skies mostly. In addition, the ridge of high pressure brought a strong southerly flow of warm moist air from the Gulf of Mexico all the way up to Minnesota, Wisconsin and South Dakota.
The warm humid air led to Excessive Heat watches and warnings across the areas. The warnings were issued as the heat index values for much of the Central United States were in the triple digits. The heat index is an apparent temperature which factors in temperature and humidity and the higher the humidity, the higher the heat index feels like. However, the extreme heat and humidity led to afternoon thunderstorms across some of the region due to the large amount of Convective Available Potential Energy (CAPE) that was present for much of the region. CAPE is the buoyancy of a parcel of air and is related to the vertical motion of thunderstorms. CAPE is higher when there is more warmth and temperature in the atmosphere. The area of the extreme heat also happens to be where most of the corn is growing in the United States, click here to find out more about how corn plays a factor in the humidity.
The hot and humid weather pattern expanded to New York and the East Coast by Friday and persisted for the weekend. However, the pattern shifted to be cooler as the new week began and the ridge of high shifted eastward. We at the Global Weather and Climate Center would like to remind you to stay hydrated and cool especially during the summer heat by drinking at least 8 cups of water a day especially during the warmest time of the day as well as staying in the shade as much as possible and to try to not do too much outside especially between the hours of 10 am and 5 pm as that is when the heat and sun is at the highest points.
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©2019 Meteorologist JP Kalb
A Case Study of the Great Plains Low-Level Jet: July 17-18, 2010 (Photo Credit: Sharon Sullivan, Weather Research and Forecasting Model - WRF)
Evolution of the low-level jet over the sloped Great Plains terrain at f14 (7 pm CDT July 17), f19 (midnight), and f24 (5 am CDT on July 18th).
A short case study is presented for July 17- July 18, 2010 to determine if there are characteristics present that define a classic summertime low-level jet. The nocturnal Great Plains Low-Level Jet (LLJ) is a fast-moving ribbon of air in the lowest level of the atmosphere (about half a mile above the surface). Wind speeds may increase to 40-60 miles per hour after midnight. The Great Plains Low-Level Jet is commonly found from Texas northward to Nebraska and centered geographically over the Oklahoma/Kansas border. Climatological analysis indicates that the low-level jet is most common in June and July, with a peak around mid-July.
There has been much debate over the past 50 years as to the mechanisms that initiate the low-level jet, but two main theories seem to emerge: Holton’s and Blackadar’s theory. Blackadar’s theory suggests that the low-level jet occurs as a result of the clockwise rotation of the nocturnal wind. Holton considered the diurnal variations of the heating and cooling of the sloping Kansas terrain to allow a pressure gradient to develop. During the daytime, a strong temperature gradient sets up from east to west along a constant height surface, where the strongest heating occurs above the highest slope of the terrain. At night, the pressure gradient reverses and the boundary layer begins to decouple from the surface layer. Both methods are acting in the LLJ, but the Blackadar method seems to dominate more.
A cross-section completed using the Weather Research and Forecasting (WRF) model, a mesoscale numerical weather prediction system, shows a weak low-level jet with a weakly-defined jet core. The wind speeds increase significantly over the region in the early morning hours, as one would expect to see with the presence of an LLJ. The jet starts to appear at f14 (7 p.m.) and reaches its maximum at f21 with wind speeds in excess of 45 mph. The jet core appears over Tescott, Kansas in this case at a height of ~3000 feet above the surface. The jet became weaker at f24 (5 a.m.) and can be seen propagating to the east. A few scattered showers developed overnight due to enhancement by the low-level jet with the tendency for the storms to move south of the low-level jet axis with time.
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© 2019 Meteorologist Sharon Sullivan