A Wooster Geologist returns to the Jurassic of southwestern Utah

Mark Wilson April 16, 2018 4:16 am

St. George, Utah — This week I’m exploring the wonderful Middle Jurassic Carmel Formation exposed in southwestern Utah. It is a rare bit of solo fieldwork I’m doing to prepare for a Wooster Independent Study expedition here with students and Nick Wiesenberg in about a month. My colleagues, students and I last did research here almost two decades ago, so I wanted to make sure I knew how access and exposures have changed. Better to explore early than be surprised while leading a team! (One new thing in the above image: a lake where I used to wade across the Santa Clara River to get to the Carmel outcrops.)

The Carmel Formation is 100 to 300 meters thick, more or less, through parts of southern Utah. It is relatively thin by Utah Jurassic standards. It is a mostly marine unit, having been deposited in a narrow restricted seaway. I’ve long been fascinated by its fossils, which are almost entirely mollusks and traces of arthropods. It is time to revisit these exposures with new eyes and ideas.

This is a view looking north across typical Carmel Formation outcrops about a half-hour northwest of St. George. The rocks are exposed in strike valleys, which are great for finding bedding plane slabs with fossils and sedimentary features, but miserable for constructing stratigraphic columns. Luckily most of that tedious work is done. In the background are two iconic mountains for the area: Square Top and Jackson Peak. In April 1983, a B-52 bomber tragically crashed into Square Top.

The Carmel Formation is capped unconformably in this region by the Upper Cretaceous Iron Springs Formation, a conglomeratic sanadstone here. It is cemented well, capping the less resistant Carmel limestones and claystones below. This is a typical strike valley exposure of the top of the Carmel.

This is a Google Maps view of today’s field area, which is in the middle of the image stretching diagonally from the reservoir in the southeast (right) to where the dirt road bifurcates in the northwest.

One of the interesting features of the Carmel is a widespread carbonate hardground. Tim Palmer and I published on it a long time ago, but there are still many questions about its formation and the variety of borings on its surface. Above are two fragments found loose in a wadi.

The Carmel has beautiful sedimentary structures, like the ripples on the left, and cool trace fossils like the arthropod trackway (Gyrochorte) on the right.

I’m intrigued with the dominant oysters in the Carmel: Liostrea strigilecula. They formed “oyster balls” (ostreoliths) almost unique to the Carmel, and these large masses of unknown origin and significance. They seem to be small reef-like forms, but also show signs of occasional overturning. They hosted encrusting bryozoans and boring bivalves.

An early morning view of my field area. The reddish unit below is the Temple Cap Formation, with the base of the Carmel white turning into, shall we say, carmel-colored. The water is part of the Gunlock Reservoir.

Today I sorted out access to a few old localities, and found some new ones. Much has changed here in the last 20 years. There are new roads in and around the growing cities of St. George and Santa Clara, the Santa Clara river has been further managed with massive earthen works (in response to frequent flash floods, no doubt), and there seem to be new barbed-wire fences across some Carmel exposures. Nevertheless it felt like old times as I tramped across the gravelly hillsides scanning the ground for geological treasures.

I must add as a footnote an image of this ugly-but-simple bridge over the Santa Clara River at Miner’s Canyon. For years my students, colleagues and I waded through the river here because the water was too deep for our rental vehicles. This meant we had lots of walking to do once we were on the other side, including walking back loaded with rock samples. Now we can just drive across. I have a feeling, though, that this bridge will not survive the next flash flood!

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Climate Monday: Repeat Photography

acrawford April 15, 2018 8:08 pm

The semester is winding down, so we only have a few more of these climate visualization posts to go. Today, I want to highlight repeat photography. Taking a picture of the same place several or many years apart can be a striking demonstration of change and capture the imagination better than a sterile graph or abstract map.

The flashiest examples applying the idea to climate change come from productions like Chasing Ice by the Extreme Ice Survey or Chasing Coral by Exposure Labs. (Chasing Coral was recently featured here at the College of Wooster as part of the “Great Decisions” series.) The products can be truly fascinating, especially when many photographs are combined in a time lapse video.  For example, the video of the Extreme Ice Survey’s repeat photography of Mendenhall Glacier, embedded below, gives a better impression of glaciers as flowing masses of ice than any single photograph or model simulation.  It also shows the decline in mass at the toe of the glacier between May 2007 and August 2011.

Rules of Climate Change Repeat Photography

Showing climate change with repeat photography requires a few special considerations:

First, you need to have not only the same location, but the same angle for your shot, showing the same context around the feature of interest in each and every photograph being compared.  This is why the Extreme Ice Survey set automated stations with the cameras well-mounted rather than using hand-held cameras.  Much of the Chasing Ice documentary is about building and installing the equipment necessary to achieve this fundamental “rule” of repeat photography. The Chasing Coral team tried similar techniques, only with the added complication of being under water.  Needless to say, it was harder for the Chasing Coral team.

Second, any repeat photography of environmental phenomena had better avoid making natural seasonal cycles look like climate change.  The two pictures of Sub Lake in Rocky Mountain National Park above were taken in June 2015 and January 2013.  The difference between the two isn’t climate change; it’s winter. Another example: The Mendenhall Glacier video shown above is labeled as “May 2007 to August 2011”.  A red outline of the glacier in the first frame is compared to the outline of the glacier in the final frame, and that’s a little deceptive.  Just like snow cover and sea ice, the Menhendall Glacier has a greater extent and thickness at the end of winter than the end of summer — especially at the toe. So part of that difference you’re seeing is just the fact that a) over 80 inches of snow typically fall on the toe of the Mendenhall from October to March and b) the average high temperature is over 60°F in June, July and August in southeast Alaska.  It’s likely to look more robust in May than August, so the time lapse would be better starting and ending in the same month.

Image result

Cherry blossoms in Washington, D.C. (from the National Park Service)

Third, climate change is not the only factor that determines whether one year is cooler or warmer or wetter or drier than the last.  Climate change is not the only factor that determines whether coral bleaching will occur or whether a glacier will retreat.  For example, in Chasing Coral, a coral bleaching event in Australia is highlighted and attributed to climate change.  At the same time, though, an El Niño event was occurring. El Niño is a natural part of the climate system, but it can also lead to warming and coral bleaching. Was global warming a factor in this bleaching event? Absolutely, but the devastation depicted in Chasing Coral may have been less overwhelming in a La Niña or normal year. As another example, if you were trying to take pictures in Washington DC to show how the date of cherry trees blooming was coming earlier each year, you might be disappointed.   Although blooming is now occurring on average about a week earlier than in the 1970s, peak bloom was actually slightly later than average this year. The best way to get around this issue is to have several decades between the start and end of the repeat photography pair or sequence.

The Repeat Photography Project at Glacier National Park

With all these rules in mind, the United States Geological Survey (USGS) is currently undertaking a repeat photography project for the failing glaciers of Glacier National Park. They’re also soliciting help from visitors in a crowd-sourcing effort. The time spans exceed 50 or even 100 years for these photos, which is enough time to see some truly remarkable changes to Glacier National Park’s namesakes. It’s even long enough to avoid the seasonal issues discussed above. As an example of the output, below is repeat photography of Boulder Glacier (1932 to 2005) from the Northern Rocky Mountain Science Center (NOROCK).

Boulder Glacier - 1932 Boulder Glacier - 2005 color

 

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Climate Monday: Putting Recent Weather in Context

acrawford April 9, 2018 7:30 pm

It snowed in Wooster today. It also snowed in Pennsylvania, Michigan, Iowa, Maryland, and several other states. Across the Northeast and Midwest, baseball broadcasters, news anchors, my coworkers, and even random people on the street are remarking on how “It sure doesn’t feel like spring”, and “why won’t winter go away.”  Actually, this refrain has been happening since a series of big storms pummeled the East Coast in March.  So of course I wonder: how uncommon has the late winter/early spring weather been?

I figure we can use this griping to highlight where to go to see past weather in context.  It’s all too easy to get a forecast for tomorrow, and it’s all too easy to complain that the weather “isn’t like it used to be”.  But let’s get critical here: Is this abnormal? Here’s a few places you can go to get an answer:

  1. Go to NOAA’s “Climate Data Snapshots“. You can quickly display the basics of climate (temperature and precipitation) for any month in the 21st century up to last month. There’s a few other options, too (like drought and climate change projections). Here’s their map for whether the USA was cooler (blue) or warmer (red) than normal last March:

So yes, the East Coast was a bit colder than normal, but only by a few degrees Fahrenheit in most places. Maybe people in eastern Montana had better reason to gripe about the weather than anybody in the Midwest or Northeast. In was 10°F colder than normal up there.

2. For a little more analysis, check out the NOAA News section. This week, they have the summary for March 2018. They provide some context in addition to the maps on this site.  They also use a different map for showing whether it’s been colder or warmer than normal.  This map is a percentile map; instead of showing how warm or cold compare to normal it was in °F, it asks, what percentage of Marches were colder (or warmer) than this one?

 

Here we can see that although eastern Montana was about 10°F colder than normal on average in March, that’s par for the course in Montana.  The temperature varies widely out there on the northern plains, so an erratic March is nothing new.  In North Carolina and Virginia, however, having a March that is 5 or 6°F colder than normal is something rare, so pockets of those states came in “much below average”.  In other words, just as the average temperature in Montana is colder than North Carolina, the temperature in Montana is also more variable than in North Carolina.

3. A third place you can go is to the professional weather and climate bloggers at Category 6 on Weather Underground. Bob Henson and Jeff Masters are more likely to put a personal spin on a story, but sometimes that’s even more interesting.  They often highlight NOAA’s maps and give their own flavor.  For example, they prefer to highlight the state-wide averages for temperature:

When you do that, the whole story of the East Coast be cold and snowy (and it was snowy, for sure) pops out even more distinctly than eastern Montana — because overall, the state of Montana was pretty average.  Some of the detail is lost for big states when state-level data are used, but they also have some appeal — it’s easier to think in states than the the divisions used in the previous two maps, after all.

So getting back to today, what do the numbers say for Wooster.  Well, Sunday April 8 was the coldest day recently, with a low temperature of 23.5°F at the weather station at the OARDC just south of town.  The record low for April 8 is 14°F, set in 1982.  The average is 33.0°F. So no, this wasn’t record cold for Wooster. But it was pretty low — only 12 years (about 10%) since 1900 had a lower daily minimum for April 8.  Also, of the 52 years with non-zero precipitation on April 8, a total of 11 of them had snow — that’s 21%.  (It drops to 19% for April 9.)  In other words, yes, it’s colder than normal…  and yes, snow is rare on April 9 in Ohio.  But not that rare.  The last time it did, in fact, was… 2016.

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A Wooster Paleontologist visits the Smithsonian’s National Museum of Natural History

Mark Wilson April 5, 2018 11:01 pm

Washington, DC — I have the privilege this semester of being on a research leave from teaching, so I thought I’d report on one of my activities. Without classroom responsibilities I can travel for research opportunities, especially now as the weather in the northeastern US marginally improves. (Despite the sunny view above, it was freezing!)

I visited the Paleobiology Department of the National Museum of Natural History in Washington to examine some particular fossils in the collections, and give a departmental seminar. This is typical for paleontological research, and I’m grateful to the generations of museum scientists who make it possible.

The Collections Manager at the NMNH Paleobiology Department is our own Kathy Hollis (’03). She does such a fine job she’s on a poster board in front of the museum, and she was featured in an excellent Wooster Magazine article on museum science.

Kathy sets me up deep in the fossil collections, endless rows of cabinets. The Paleobiology Department, in fact, has more than 10,000 of these, each with multiple drawers of treasures.

My work is pretty simple at this stage. I find fossils of interest in the collections (most of which I’ve identified from publications) and photograph them for future reference. I use this copy stand, which is the best in the business. (I want one, Department Chair.) The paper tray is filled with lead shot which is useful for positioning specimens at any angle under the camera.

Here’s an example specimen: the ambonychid bivalve Claudeonychia from the Upper Ordovician of the Cincinnatian region. The scale is in centimeters. The dark color is actually an encrusting bryozoan, a story I’ll tell later.

I meet many cool fossils along the way, including this magnificent specimen of Wilsonoceras from Wyoming. It is a nautiloid cephalopod I’ve always wanted to see purely for its name!

Here is the poster for my presentation to the Paleobiology Department. It is a tradition for visiting researchers to present a talk on their work.

This is the Cooper Room where the talks are held. I love its Old School ambiance, and the paleontological history it represents. It is a superb place to present ideas to colleagues in the discipline.

The field season is about to begin for Wooster Earth Scientists, so expect more posts. Again, it is a privilege to have such opportunities.

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Climate Monday: Climate Change Hot Spots

acrawford April 2, 2018 7:32 pm

It’s no secret that global warming does not simply mean more warm days and fewer cold ones. Warming is uneven, with some regions (like the Arctic) warming faster than others. Additionally, warming of the atmosphere and oceans has a cascading effect on other parts of the Earth system, from the amount of ice stored in Greenland to the variability of global wind patterns, to the extent of various habitats. The world is complex, and it the impacts of climate change myriad. With so many changes happening, what places or changes should humans focus adaptation and mitigation efforts? Enter the concept of “climate change hot spots”. Let’s examine three frameworks and how they’re visualized.

Example #1: One of the simplest frameworks for talking about climate change hot spots is to consider places where various physical aspects of the climate are projected to change the most (Kerr 2008). This was the tactic used by a group of climate modelers from the National Center for Atmospheric Research back in 2008.  They ran detailed, regional-scale climate models into the future and looked for a) places with the most change in average temperature and precipitation, and b) places with the most change in the variability of temperature and precipitation (in other words, heat waves, cold snaps, floods, and droughts).  The result was a relative index from low change to high change:

Figure 1: Map of the “relative responsiveness” of the USA and northern Mexico to climate change based on projected changes in temperature and precipitation under a suite of climate models. (Kerr 2008)

The nice thing about this measure is that it’s objective and gives a value of overall impact for everywhere in the lower 48.  It’s limited in it’s utility, though.  For one thing, it only measures temperature and precipitation, omitting related concepts like sea level rise and wildfire frequency/intensity.  It also is a projection of the future, which is problematic both because there’s less certainty about the future and because there are changes already happening that might be more pressing to address.

Example #2: That in mind, another way to define “climate hot spot” is a location that has already changed substantially. The Union of Concerned Scientists (2011) has compiled a map of locations that have “well-documented” changes already occurring. Here’s a snapshot, but the visualization is meant to be an interactive map, not a static image, which is certainly inviting.  The “well-documented” claim is supported by reference lists and descriptions for each event. In other words, these have been researched substantially.  Another interesting point is that the map shows a much broader view of “climate change” than the earlier climate model studies.  Sure, there’s “extreme wet” and “air temperature”, but there’s also “ecosystem” sections and “health” and “food” for people. This is definitely better suited for a broader audience and broader concerns.

Figure 2: Snapshot example of climate hot spots by the Union of Concerned Scientists (2011).

Still, the above example may seem lacking with regard to two elements (and maybe others): First, it is clearly focused on the USA.  There is a data bias, of course — the Union of Concerned Scientists has many American scientists, and many of them study the USA. But it may give the false impression that the USA has more dire situations than the rest of the world.  Second, there is still little sense of risk versus vulnerability.

If we think of climate change as a natural hazard, just like a volcanic eruption or an earthquake or a hurricane, we can talk about both risk and vulnerability of populations.  For example, both the Netherlands and Florida are at great risk of sea level rise, but the Dutch are bettered prepared to adapt to rising seas because of past experience and current cultural, political, and physical infrastructure. The same risk can lead to more or less hardship depending on how vulnerable a place is — and assuming sea level rises about the same in both locations, Florida is likely to have more hardship from sea level rise than the Netherlands.

Example #3: This added concept of vulnerability is used to define “climate hot spots” in yet another way: as locations where “strong physical and ecological effects of climate change come together with large numbers of vulnerable and poor people and communities” (Neumann and Szabo 2016). Their map is still really a measure of risk, not vulnerability, but they use it to help highlight areas with high risk that also have special vulnerability (originally identified by De Souza et al. 2015):

  1. Deltas in Africa and South Asia that have large populations of poorer people. Groundwater extraction and other human activities that make deltas sink can exacerbate the effects of sea level rise.
  2. Semi-arid regions in parts of Africa, South Asia, and Central Asia that may become drier. Again, the lower economic resources in these regions make them more vulnerable.
  3. River basins dependent on glaciers and snowpacks as a water source, especially in the Himalaya, where there are large populations of poorer people.

Figure 3: Climate risks based on three factors: snow-dependence, semi-arid climate, and river deltas. (Neumann and Szabo 2016).

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Works Cited

De Souza, K., Kituyi, E., Harvey, B. et al.  (2015). Vulnerability to climate change in three hot spots in Africa and Asia: key issues for policy-relevant adaptation and resilience-building research. Reg Environ Change, 15: 747. https://doi.org/10.1007/s10113-015-0755-8

Kerr, R. (2008). Climate Change Hot Spots Mapped Across the United States. Science, 31: 909. http://science.sciencemag.org/content/sci/321/5891/909.full.pdf

Neumann, B. and Szabo, S. (2016). Climate change ‘hotspots’: why they matter and why we should invest in them. The Conversation. Accessed 2 Apr 2018. http://theconversation.com/climate-change-hotspots-why-they-matter-and-why-we-should-invest-in-them-68770

Union of Concerned Scientists (2011). Climate Hot Map. Accessed 2 Apr 2018. http://www.climatehotmap.org

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Climate Monday: Weather Forecast Maps

acrawford March 26, 2018 2:02 pm

The College of Wooster is now back in session for six more weeks, which means we have six more climate visualizations to share this semester. Today is bright, sunny, and quickly approaching 50°F in Indiana, Ohio, and Pennsylvania, but we’re due for a rainy week, so it seemed like a good time to highlight weather forecasts.  In the USA, we see forecasts for our localities frequently.  Maps or descriptions of current and future weather conditions are pervasive throughout the various forms of media, from phone apps to newspapers to radio broadcasts.

Below is the current weather surface according to The Weather Channel.  There’s high pressure currently centered over the northeast — hence the clear skies, but a storm is brewing over the Oklahoma panhandle.  Over the next few days, that low pressure center is going to move eastward and northward, shoving that precipitation you currently see over Missouri along with it and generating more along those fronts as it strengthens.  I like The Weather Channel current surface maps.  They’re neat, colorful, easy to read, and only show the essentials needed to understand the current weather state.  However, they don’t have a similar map for forecasts.

Current US Surface Weather Map

For example, if you go to the “Classic Weather Maps” section of their website, and then scroll down to learn what’s in store for Wednesday, I you see this:

Day 3 Forecast

 

That not too bad for many people.  Find a city near you, look at the symbol and the high temperature, and you get a good sense of how to dress. However, if you’re halfway between cities shown, like Wooster or the middle of Iowa or Oregon, this map is less helpful. Is is going to rain in Wooster like Cincinnati or just be cloudy like Detroit? Also, there’s a lack of context — there’s no marking of high and low pressure to help give a sense of the atmospheric circulation behind these weather forecasts.  If you’re interested in your locality, you probably want a map that’s zoomed in further, so this national map isn’t helpful. And if you’re a weather geek, you probably want more detail.  So this forecast map may not be what you’re looking for.

Another option is Weather Underground. This website is a bit geekier than The Weather Channel, and it’s especially cool that you can link up your own personal weather station data to their server for free and share it with the world.  Their main forecast map for Wednesday morning (shown below) is dominated by the precipitation.  No cities or cloud/sun symbols are shown, but you probably know where you live and can surmise that a place receiving that light green shade will be cloudy with some showers, whereas the dark green is a sure thing for steady rain at least part of the day.  It’s a little easier to gauge the broader context here, too.  That big band of rain from Texas to upstate New York is a classic signature of a winter storm (yes, “winter”… “extratropical cyclone” is more accurate, but also less commonly said) that’s moved across the Heartland and currently sits in the northeast, a big cold front extending down to the southwest.  But the front isn’t drawn; neither is the low pressure symbol.  There could be more.

Both The Weather Channel and Weather Underground are primarily weather communicators and collectors. They do not actually make the forecasts; rather, they receive forecasts from the National Weather Service (a branch of the National Oceanic and Atmospheric Administration, or NOAA). If you aim for Wednesday from NOAA, you get this map:

For the weather geeks, this is the best map.  It has the precipitation forecast, but it also shows the fronts and the pressure.  The context that can be inferred from other maps is plain and explicit here.  This is definitely not the prettiest map, and if you’re not a weather fan, it might seem pretty cluttered.  However, if you like clutter, check out this forecast map from Unisys:

NAM - US - SL Pres/Prec - 48hr

Personally, I think that is not a nice color scheme, and the number of “Highs” and “Lows” indicated is a tad excessive.  But there’s a lot of data on this map, and that can be useful for analysis even if it fails at communication. In the end, the map you choose likely depends on your personal preference!

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A geological and archaeological hike in northeastern Ohio on the last day of winter

Mark Wilson March 19, 2018 9:14 pm

It was a beautiful latest-winter day in Wooster. Nick Wiesenberg had the great idea of taking an afternoon to hike through Pee Wee Hollow, a wooded area of ravines, streams and rocky exposures a few miles northwest of Wooster near the village of Congress. Greg Wiles, his faithful dog Arrow, and I went along. We had an excellent time with no agenda but to explore. Above is Dr. Wiles standing at an outcrop of Lower Carboniferous sandstones, shales and conglomerates making up the Logan Formation. The rocks are similar to those exposed in Spangler Park.

Pee Wee Hollow has three small Native American mounds on an upper plateau. Nick and Arrow are standing on one above. They were excavated in the 1950s, and possibly pillaged long before that. Dr. Nick Kardulias, Dr. Wiles and several others wrote a paper on these mounds. I can quote the abstract entirely: “While a great deal is known about the many earthworks of central and southern Ohio, there is a gap in our data about such features in the northern part of the state. The present report is an effort to bring work on one such site in Wayne County into the literature. The Pee Wee Hollow Mound group consists of three small circular earthen structures and a possible fortification trench on a high bluff overlooking the main stream that drains the county. Systematic excavation by avocational archaeologists in the 1950s revealed the structure of the mounds and retrieved a small assemblage of artifacts, some charcoal, and pockets of red ochre. Recent analysis of the artifacts, coupled with radiocarbon dating, indicates that the site was a location of some local importance from the Late Archaic through the Middle to Late Woodland periods.” (Pennsylvania Archaeologist 84(1):62-75; 2014)

Another of the mounds with Greg and Arrow for scale.
The very fine sandstones of the Logan Formation are especially well exposed in the creek beds. Here are a set of joints our structural geologist Dr. Shelley Judge would appreciate.

There are even some nice Bigfoot field structures. Who knew?We spent most of our time walking up Shade Creek. The creek bed is mostly Logan Formation sandstones.

Greg is standing here on a bedding planes of sandstone with nice ancient ripple marks. Note, by the way, the chunk of ice above his head. Still winter, but not for long.

Here’s a closer view of those ripples.Arrow here contemplates a thick exposure of dark gray shale. Greg found some nice crinoid columns in it, and I found several molds of bivalves.

The more resistant units in the Logan have the best fossils. This slab of very fine sandstone cemented with iron carbonates (a type of siderite concretion) has several internal molds of brachiopods and white calcitic crinoid columns. I described the remarkable preservation of similar crinoids in an earlier series of blog posts.

A nice, uncomplicated walk in a beautiful bit of nature.

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Climate Monday: Visualizing the South Asian Monsoon

acrawford March 5, 2018 9:05 pm

Last Monday I posted some diagrams, animations, and predictions for El Niño and La Niña. So this week we’ll shift from the Pacific Ocean to the Indian Ocean and check in on the South Asian monsoon.  “Monsoon” is really just another word (of Arabic origin) for “season”, but it’s typically used to describe places with distinct wet and dry seasons caused by a reversal in the dominant regional winds.  There are several factors that impact any monsoon, and in India three important ones are:

  1. The position of the “Intertropical Convergence Zone” (ITCZ)
  2. Land heats up and cools down much more easily than water.
  3. The Himalaya

Although the relative importance of #1 & #2 for South Asia is still debatable, most traditional explanations focus on #2, possibly because it is easier to explain…

Figure 1 is a diagram from Thomas Reuters that depicts the traditional explanation for why monsoons in South Asia (and elsewhere) occur.  The theory goes that:

  1. Land heats up rapidly during summer, while the ocean heats up slowly, so the land surface ends up hotter than the ocean surface.
  2. Hot air is less dense, making it buoyant and likely to rise.
  3. Rising air over land is replaced by cooler ocean air from the southwest, which brings ample moisture with it.
  4. This moisture-bearing air then rises over the Indian sub-continent, cooling down, which causes condensation (cloud formation) and rain, rain, rain.

In winter, this all works in the opposite direction:

  1. Land cools down more quickly than the ocean, so by mid-winter the air over the ocean is warmer.
  2. Rising air is limited to the ocean, and India experiences sinking air instead.
  3. On top of that, winds blow from the northeast over India to replace the air that’s rising to the south, and those northeasterly winds are dry because they come from interior Asia.

In this way, land-sea contrasts help form the monsoon — a seasonal oscillation of southwest to northeast winds and wet to dry seasons.  You’ll see this same description in many animations of the monsoon, too, like this one from NASA:

However, these explanations are incomplete.  Land-sea contrasts are just one factor impacting monsoons.  If they were the only factor, we’d expect monsoons to exist everywhere with a strong warm/cold season and a land/sea boundary. We’d also expect monsoons to be absent anywhere without a strong land/sea contrast or warm/cold season.  Neither of these is true.  The Sahel in Chad is far from any ocean but has a monsoon climate, and islands like the Galápagos and New Caledonia have a monsoon despite being surrounded by the Pacific Ocean.  Meanwhile, places like North Carolina and France have strong winter/summer contrasts in temperature but no clear wet/dry season, and even coastal places like San Francisco, USA or Luanda, Angola, which have distinct wet/dry seasons, lack the wind reversal characteristic of a monsoon.

Figure 2: Seasonal shifts in the Intertropical Convergence Zone (ITCZ) — the main tropical rain belt. (Image Credit: Mats Halldin)

The South Asian monsoon cannot be understood without another aspect: the Intertropical Convergence Zone (ITCZ). This is a zone of hot, rising air throughout the tropics.  This air cools at it rises, causing condensation and rainfall.  It occurs primarily because the tropics receive more direct sunlight than anywhere else in the world, and because of that solar control, the ITCZ drifts northward in May through July and southward in November through January, following the Sun.  It happens over land and water alike, but the shifting tends to be more prominent over land areas, which can heat up and cool down more quickly. In other words, when you combine the concept of land-sea contrast with the concept of the ITCZ, its understandable that the monsoon in South Asian is particularly strong. Both are working in concert.

You can see the progression of the monsoon northward across India throughout June and July (Figure 3).  It’s mostly a south-to-north progression, but also largely east to west.  Again, this is due to a convergence of factors, not just land/ocean heating contrasts.

Figure 3: Progress of the 2016 summer monsoon in India compared to normal. (It was a late monsoon year.) Source: India Meteorological Department.

However, the South Asian monsoon also would not be nearly so strong without the Himalaya — the highest mountains in the world.  These mountains are so imposing that they effectively block advancement of winds blowing from the southwest.  Warm, moist air from the Indian Ocean stalls out in the Himalayan foothills, making Bangladesh the wettest place on Earth.

This video and animation from JeetoBharat, an Indian mentoring and test-prep organization, does a better job incorporating the multiple facets of the South Asian monsoon:

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Climate Monday: Visualizing El Niño and La Niña

acrawford February 26, 2018 1:20 pm

Continuing our survey of climate and weather visualizations, this week we have a few ways of visualizing El Niño and La Niña, which are two flavors of the El Niño-Southern Oscillation (or ENSO).  This is a relevant topic for this winter, because the world is currently experiencing a La Niña episode.

The best way to fully grasp the El Niño Southern Oscillation is probably through animations that can give a 3-dimensional perspective, because the whole system depends on interactions between the ocean and atmosphere throughout the entire equatorial Pacific Ocean — which stretches for a little under 1/2 of the entire Equator.  It’s a complicated system, and using just words is inadequate.  Here’s one example from Keith Meldahl, a professor at MiraCosta College:

If you prefer a British accent and a more formal presentation, here’s an animation from the UK Met Office:

To summarize, these animations are showing how ENSO works and how it impacts precipitation in the tropical Pacific. Normally, ocean currents and wind at the surface both bring air and water  from east to west, pulling water away from South America.  This keeps the coast of Peru and Ecuador cooler and drier than you might expect, because cold water from the south and from deep in the ocean moves in to replace the water being pushed to the west.  Meanwhile, Indonesia, Papua New Guinea, and Oceania receive ample rain from the warm currents and warm winds.  This hints at a key concept in hydrology and meteorology: air that starts out cold is unlikely to provide much rain, but air that starts out warm and then rises and cools? That’s a rainmaker. During an El Niño event, the winds and ocean currents are weaker, so there’s less pushing of the warm air to the west, and the area where rain occurs drifts to the east.  During a La Niña event, the winds and currents are stronger, so there’s more pushing to the west, and the area where rain occurs drifts west.

That’s great for visualizing the physics, but to see what’s going on right now, a great place to visit is the National Oceanic and Atmospheric Administration’s ENSO website. The easiest way to measure whether we’re in neutral conditions, El Niño, or La Niña is to measure the temperature of the ocean surface (a.k.a. “sea surface temperature” or SST) using satellites. When El Niño occurs, there’s weaker currents and less upwelling of cold water off the coast of Peru, so the sea surface is warmer than normal.  When La Niña occurs, there’s more upwelling of cold water than normal, and the sea surface is colder than normal.  We’re are in a modest La Niña right now, and it’s starting to weaken. Here’s the data from January 2018:

This map shows how sea surface temperatures along the Equator compared to normal for January of 2018. Blue color shows that the sea surface was colder than normal along the Equator — a La Niña event (from NOAA). Data come from a combination of satellites managed by the USA, Japan, and Europe.

The last question we might consider is: Does this have any impact on the USA?  The answer is: some impact, but it’s indirect.  El Niño and La Niña influence the location of the jet streams, narrow regions of strong winds that direct most of our weather in the USA. The jet streams bring rain. The USA is mostly dominated by the polar jet stream, but during El Niño years, the polar jet stream is pushed to the north, and a secondary jet stream develops in the south — often right through Arizona, Texas, and Florida. So the southern tier of the USA tends to be wetter during El Niño events and drier during La Niña events.  La Niña events are often some of the coldest in the northern Great Plains of the US and Canada, and El Niño some of the warmest.

For Ohio, La Niña events actually end up being a little wetter because the polar jet stream is more often sitting right over us (like it was nearly all of last week!). Note, ENSO has only a weak to moderate influence in much of the USA, but it is part of what shapes our winter weather!

Typical winter weather patterns for North America during La Niña and El Niño events. (from NOAA)

More El Niño:

An overview from the UK Met Office

The 2015-2016 El Niño Event (by ECMWF)

El Niño for Kids (by NASA)

 

 

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A warm February afternoon in Spangler Park

Mark Wilson February 20, 2018 6:11 pm

Wooster, Ohio — The weather today was extraordinary. It reached at least 70°F in our little Ohio town, which must be near a record. Greg Wiles, Nick Wiesenberg and I took advantage of the warmth and sunlight to hike through Spangler Park. I think the day should be memorialized with a brief blog post. Greg and I are on research leaves this semester, so it is easy for us to break away from our computers to take jaunts like this. (Sorry, Meagen, Shelley, Alex and Karen!)

Above is a familiar exposure to most Wooster Geologists. It is an exposure of glacial sediments visited by dozens of department field trips. Recently a slump block descended across the face of it, exposing new material. Nick is standing on the block, and Greg’s dog Arrow is watching at a prudent distance.

Chloe Wallace (’17) posted this nice description of this outcrop two years ago:

This photo is taken from across Rathburn Run, from the point bar. This outcrop is much younger in age, from the last time Ohio was affected by glaciation. During the Last Glacial Maximum, specifically the Pleistocene, glacial debris flows deposited the bottom section of the outcrop. The sediment is characterized by a fining upwards sequence and has two scales of support. Some areas of the deposit are composed of large grains within a matrix-support due to debris flow. Other areas of the deposit are composed of sandy conglomerate rock that is grain supported. Overall the sediment is poorly sorted and contains glacial erratics within the sediment, including boulders made of gneiss, granite, and some sedimentary rocks.

A channel cut through the original glacial debris flow deposit and was eventually filled in by wind-blown silt, also known as loess. Loess is characteristically different from the glacial deposit at the bottom of the outcrop. Loess breaks in sheets, which causes it to have steep angles. Overall, the history of this outcrop is that approximately 15,000 years ago debris flow events deposited the glacial sediment at the bottom of the outcrop, then a channel cut into the deposit and that channel eventually filled with eolian (wind-blown) silt.

Classic geology on a beautiful day.

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