Gwen Howell Levey ERTH 365.01 Lecture #8 Notes April 2, 2020 OVERVIEW

● Further processes for warming and cooling the atmosphere ● Cold and warm core low pressure systems ● Hurricanes in depth ● review for Homework (supplemental notes)

WARMING & COOLING THE ATMOSPHERE

Another way of warming air:

● 1. Physicists tell us that when water vapor condenses, a certain amount of thermal energy is “given” to the atmosphere. In short, condensation is a warming process. ● 2. The amount of heating is proportional to the amount of water that condenses. At sea- level temperature and pressures, the warming is about 590 calories for each gram of water that condenses. The 590 calories is known as “latent heat" ○ The more that water condenses, the more heat goes into the atmosphere ● 3. Since air with 100% relative humidity at lower dew point temperatures holds less water vapor than air with 100% relative humidity at higher dew point temperatures, much more heat is liberated in cases which cloud development is occurring in high dew point environments. ○ The warmer the air, the more moisture that it can hold. ○ Much more heat will be released in a latent environment because of water vapor in the environment. ● EXAMPLE: ○ Air that has 100% relative humidity at 10˚C has about 8g of water vapor per kg of air, while air that has 100% relative humidity at 30˚C has about 32 g/kg. If the kilogram air parcel initially at 10˚C is lifted and cooled so that all of the water vapor condenses out of the parcel, approximately 4720 calories would be liberated. Similarly, if the 30˚C parcel were also lifted, 18880 calories would be liberated as it rose. ■ A lot more energy is released into the atmosphere in warmer environments when we have clouds forming. ○ The tremendous heating due to latent heat release makes the core of hurricane and monsoonal thermal lows that have access to humid air much warmer, say, at 500 mb level, than can be accounted for by the actual surface temperatures alone. ■ Condensation is heating up the middle levels of the atmosphere. ○ The same sort of heating also occurs when very humid air (with high surface dew points) is lofted in the warm sector of mid-latitude wave . This excess heating is so marked that the air parcels become like hot air balloons that accelerate their upward progress if they are warmer than the surrounding air at the same elevation. This accounts for the blossoming of cumulonimbus clouds (and therefore thunderstorms) in areas with high dew points.

Another way of cooling air:

● 1. Conditional Cooling ○ Air flows over a cold surface and is cooled by conduction (this process is termed “advection cooling”). If the cooling is sufficient to take the air parcel’s temperature to the dew point, the resulting condensation will produce a layered cloud on the ground. ■ APPLICATION: California’s coastal summer advection fog ● Warm air comes over the cold ocean. The ocean cools the air which causes the parcel of air to hit the dew point temperature. From here, fog will form. ● If the dew point temperature is not reached, then fog will not form. ○ Air “sits” on a surface that gets cold overnight. (This process is termed “radiation cooling” ). If the cooling is sufficient to take the air parcel’s temperature to the dew point, the resulting condensation will produce a layered cloud on the group. ■ APPLICATION: California’s Central Valley winter “tule”/radiation fog ● 2. Expansion Cooling ○ Air expands, molecules get “further apart”, do not strike each other as often, do not “vibrate” as much. Air expands the pressure around moving air parcels decreases markedly.

■ ○ APPLICATION: ■ Rising air experiences cooling at a “dry adiabatic rate” of 5.5˚F/1000 ft. This is one of the ways in which the air is cooled to the dew point. Air moving in vertical motion is a good example of this. ●

Review:

● Two types of vertical motion: ○ 1. Buoyant/Thermal/Warm Core ■ Air rises because it is less dense than its surroundings ■ Typically occurs in warm cores with low pressures ○ 2. Forced/Dynamic/Cold Core ■ Up over a hill ■ Warmer air over colder air ■ Horizontal convergence ● Cold Core Low Pressure ○ Rising air in all levels of atmosphere ○ Cover a relatively small synoptic scale area compared to high pressure systems. Their path can heavily influence precipitation totals ○ Developed cold core lows tilt to the northwest with height

■ ● The lines in this diagram represent constant surface level pressures going up into the atmosphere ● The main thing to gather from this is that air does not rise vertically. ○ Coldest temperatures are at center of low pressure system ○ Air is called by adiabatic expansion and evaporations cooling of rain and/or snow ○ Most mid-latitude cyclones are cold-core lows ■ 99% of mid-latitude cyclones are not hurricanes (they are cold cores) ○ They cause widespread precipitation ○ They are deep cored. Developed cold core lows will show at each mandatory level. They will have closed height contours in the low levels and show as a synoptic scale trough in the upper levels. ■ We see air rising and we know that it is rising in a slanted way in each of the levels of the atmosphere ● Warm Core Low Pressure ○ Type 1: Thermal Low ■ Thermal lows are shallow and most intense at the surface ■ Develop due to strong surface heating. Hot air due to intense thermal build-up results in positive buoyancy at the surface ● Air is less dense. ■ Mid and upper levels of the atmosphere are stable ■ ONLY FORM OVER LAND ■ Most common in SW US during Summer ■ Develop over land (especially dry land with little vegetation)

■ ● This diagram demonstrates the dip at the surface that occurs where the low pressure system resides. ● This dip is most intense at the surface. By the middle layers, there are no more kinks in the pressure layers. ● Air becomes stable above 850 mb. ○ Type 2: Tropical Low ■ Deeper than thermal low, although they do weaken with height in upper levels ■ Subsidence (sinking air) in center causes compressional warming ■ Air rises rapidly around edges of (eye-wall) ● Rises directly up into the upper levels of the atmosphere ■ ONLY FORM OVER WATER ■ Warm core low is strongest when vertically stacked. Significant wind shear will weaken warm core low. This is the opposite situation of a cold core low; strong cold core lows tilt with height.

■ ● This diagram shows that air is rising all the way to the middle and upper layers of the atmosphere. ● Air is sinking in the center of the low pressure. ■ Why is air sinking in the center (eye) of the low pressure system (hurricane)? ● Centrifugal force operate outwards and cancels the effect of friction once speeds reach 74 mph, so air can not cross the isobars right near the center

○ ● A partial vacuum is caused, so air must be replaced and sinks from above, causing clear, calm conditions. ● The last closed isobar is the eyewall. ● The air in the center is rising and leaving at the same time. This is why the vacuum effect is created. ●

HURRICANES IN DEPTH (TROPICAL )

● What is a ? ○ Warm core ○ Cyclonic system over tropical waters ○ ~5˚ to 25˚ N/S latitude ■ But not at Equator because there is no Coriolis Effect here (CF)=0 ○ Counter clockwise rotation in the Northern Hemisphere ○ Classification: ■ Tropical Disturbance ● No circulation ■ Tropical Depression ● Max sustained winds less than or equal to 38 mph ■ Tropical Storm ● 39 to 73 mph ● Occurs either post or pre hurricane ■ Tropical Cyclone (aka Hurricane) ● More than or equal to 74 mph

■ ● Tropical Cyclone Naming ○ Hurricane ■ Carib god ‘Hurican’, Mayan god ‘Hurukan' ■ Location: N Atlantic, Northeast Pacific Ocean ○ Worldwide called ■ (the NW Pacific Ocean) ■ Severe tropical cyclone (the SW Pacific or SE ) ■ Severe cyclonic storm (N Indian Ocean) ■ Tropical cyclone (SW Indian Ocean) ● Hurricane Season- based on sea-surface temperature ○ Atlantic Ocean (June 1-November 30) ○ Eastern Pacific (May 15-November 30) ○ Western Pacific (Year Round) ■ Sea surface temperatures here tend to remain above 82˚F ○ Indian Ocean (April-December) ● Tropical vs. Midlatitude Storms ○ Warm cores dependent on warm water ○ Cold cores dependent on differences in air-masses ○ Warm vs. cold core ○ Fronts vs. no fronts ○ ~ 1/3 size ● Tropical Cyclone Ingredients ○ Warm tropical waters (5˚ to 25˚ N/S latitude) ■ More than or equal to 82˚F or 28˚C ■ Gigantic heat engine ■ Release of latent heat ○ Weak upper winds ■ Little wind shear because we need a warm core low ■ More wind shear during typical El Niño, therefore, we don't have very many hurricanes ■ Air has to rise vertically ● Typical Atlantic Cyclone Regions ○ ● Tropical Cyclone Formation ○ Begin as Tropical Disturbances (Easterly Wave) ○ 90% die out before becoming a Tropical Depression ○ Small clusters of thunderstorms ○ Cape Verde is a favored region (especially in July and August) ○ Example of an Easterly Wind:

■ ● Hurricane Structure (Satellite Image) ○ ● Wind Field

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VERY IMPORTANT HURRICANE DIAGRAM

● FIRST: ○ ■ Inflow at the surface ■ Air is spiraling in towards the center of the hurricane ■ Regions of rain and no rain ■ In the upper levels, we see some outflow because air is rising in certain regions ● SECOND:

○ ■ Most important part of the hurricane is the eye ■ The strongest winds occur around the eye ● THIRD: ○ ■ Arrows going up are rising air in the spiraling cloud bands that come in towards the center of the hurricane. ● FOURTH:

○ ■ Air that goes up in the eye wall must be replaced ■ Air sinks in between regions where air is rising ■ Subsiding of air ● FIFTH:

○ ■ In the upper levels we have air that is being vented out ■ Air diverges ● ALL TOGETHER:

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Hurricane Eye

● Average 15 mi diameter ● Range 3.5 to 60 mi ● Eye Wall ○ Outer perimeter of eye ○ Most intense storm activity ○ Strongest winds, thickest cloud cover, most intense precipitation ● Inside Eye ○ Blue skies, calm winds, no precipitation, fair weather cumulu

○ ● Shrinking Eye= intensifying hurricane Cross Structure of a Hurricane

●

Hurricane Miscellany

● Length of time ○ Average= 8 days ○ Longest= 31 days Hurricane/Typhoon John 1994 ● Average forward speed= 14 mph ● Diameter ○ 50-500 miles ○ Average= 100-200 miles ● Most Intense ○ ■ 190 mph ■ 870 mb ■ 1400 mi diameter

Hurricane Climatology

● Atlantic Basin ○ Average: ■ Tropical Storms: 10 ■ Hurricanes: 6 ■ Major Hurricanes: 2 ○ Most: 2005 ■ Tropical Storms: 27 ■ Beta, Gamma, Delta, Epsilon, Zeta ■ Hurricanes: 13 ■ Major Hurricanes: 7 ● US Hurricane Climatology ○ Deadliest: ■ 8,000-12,000 Galveston (1900) ■ 1,836 Lake Okeechobee (1928) ■ 1,336 ○ Costliest ■ $75B- Hurricane Katrina (2005) ■ $60B- (2012) ■ $45B- (1992) ■ $13B- (2011)

Tropical Cyclone Tracks

●

Hurricane Tracks

● ● Mostly follow a C shaped pattern ● Most do not make landfall ● Some Hurricanes do some crazy things and do not follow the C shaped pattern:

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Tropical Cyclone Regions

● Only case where there was a Hurricane in the South Atlantic:

○ ● Central Pacific (Hawaii) ○

Cyclone Tracks

● June

○ ● July

○ ● August ○ ● September

○ ● October

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Hurricane Season ● ● Why do most hurricanes occur in September? Because this is when the Atlantic Ocean is the warmest it will be all year.

US Landfalling Hurricanes

● Most of them are in the Gulf of Mexico, Florida, and the coastlines of South and North Carolina

●

Hurricane Naming

● Saint’s names in Latin America ● WW2 Military names ● 1950-1952 Phonetic alphabet ● 1953-1978 Women’s names ● 1978-present ○ Mixed names by WMO ○ Male/Female ○ Anglo, Latin, French

● ● Retired Hurricane Names:

○ ○ A total of 77 names have been retired since 1954

California Tropical Storms

● Only One Hurricane ○ October 2, 1858 ○ San Diego ● Only one tropical storm ○ September 25, 1939 ○ Long Beach ○ 45 fatalities, most fishermen ○ One of 4 1939 storms impacting CA ● Our water temperature is too cold

Saffir-Simpson Scale

● Category 1 ○ 74-95 mph ○ > 980 mb ○ Flooded coastal roads ○ Minor pier damage ○ Surge 4-5 feet ● Category 2 ○ 96-110 mph ○ 965-979 mb ○ Flooding 24 hours before eye, piers damaged ○ Surge 6-8 feet ● Category 3 (MAJOR) ○ 111-130 mph ○ 945-964 mb ○ Small buildings destroyed, flooding 3-5 hours prior ○ Surge 9-12 feet ● Category 4 (MAJOR) ○ 131-155 mph ○ 920-944 mb ○ Major flooding, major damage ○ Surge 13-18 feet ● Category 5 (MAJOR) ○ > 155 mph ○ < 920 mb ○ Flooding, extreme damage ○ Surge > 18 feet ● Frequency: ○

Tropical Cyclone Hazards

● Storm Surges ○ Ocean can rise up to 25 feet ○ Surface wind converges ○ Surface water diverges ○ Huge “dome” of water pushed ahead of storm

○ ● High Winds ○ Gusts up to 200 mph ○ Hurricanes are right handed: and winds are higher on right side:

■ ● Flooding from Rainfall ○ Up to 40 inches of rain ● Tornadoes ○ Spawned by the hurricane up to 1000 miles inland ○ Clusters of Tornadoes ○ Most often right front quadrant ○ Occur away from center ○ Landfall spawns tornadoes

Hurricane Fatalities

●

Worst Storms

● Galveston Texas ○ 1900, Galveston Island, Texas ○ 9 foot Storm Surge ○ Single Deadliest Natural Disaster in US History ■ Over 6,000 people drown in rising seas ■ Few took the warning ■ Visitors went to see the waves ● Bangladesh (East Pakistan) ○ 1970- 500,000 killed by Cyclone Bhola ○ 1991- 130,000 Killed ○ Near sea level ○ Poor construction ○ Most people killed by flooding ● Andrew (1992) ○ Hit south of Miami ● (1998) ○ Came ashore in Honduras ● Hurricane Isabel (2003) ○ Came ashore in the Carolinas ● Hurricane Katrina (2005) ○ Worst hurricane to ever make landfall in the ● Tropical (May 2008)

Hurricane Forecasting

● Tropical Prediction Center, Coral Gables, FL ● “Hurricane Hunters” fly into storms ○ Radar and Dropsondes ● Computer Models (NWP) ○ Statistical Uses information from past hurricanes ○ Dynamic Current information plus laws of physics ○ Hybrid Combination of both

Hurricane Watches & Warnings

● Hurricane Watches & Warnings ○ Watch ■ Landfall predicted in more than 24 hours ■ Shown by a pink line on weather maps ○ Warnings ■ Landfall predicted in less than 24 hours ■ Shown by a red line on weather maps ○ Unpredictability makes decision difficult ■ Evacuation ■ People killed ■ Costs

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