Archive for the ‘weather’ Category

Urban Heat Island

December 10, 2017

On 01 December 2017 I didn’t see any Autumn Meadowhawk dragonflies (Sympetrum vicinum) during a photowalk along Easy Road at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA.

In contrast, I saw several Autumn Meadowhawks perched on man-made structures such as a concrete curb in the blacktop parking lot at the refuge. All of the dragonflies were perched on vertical surfaces that received more direct insolation than horizontal surfaces. The parking area seems to be an urban heat island microclimate that exists within a larger natural area.

Male 1

The first individual is a male, as indicated by his terminal appendages. Although the male is missing one of four wings, he was able to fly well enough to move to three different perches along the curb.

01 DEC 2017 | Occoquan Bay NWR | Autumn Meadowhawk (male, injured)

01 DEC 2017 | Occoquan Bay NWR | Autumn Meadowhawk (male, injured)

01 DEC 2017 | Occoquan Bay NWR | Autumn Meadowhawk (male, injured)

Male 2

The next male has a full set of four wings; his wings are tattered slightly, as expected toward the end of dragonfly season.

The last photo shows the male grooming and excreting at the same time.

Related Resources

Copyright © 2017 Walter Sanford. All rights reserved.

Advertisements

“Winter Meadowhawk” dragonflies

December 8, 2017

The season called “winter” is defined two ways: atmospheric scientists, including meteorologists and climatologists, define winter as the three-month period from December to February; astronomers define winter as the time period that begins on the December Solstice (12/21) and ends on the March Equinox (03/21), although the actual dates for these events may vary slightly.

Several Autumn Meadowhawk dragonflies (Sympetrum vicinum) were spotted on the first day of climatological winter at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA. Therefore I think it is appropriate to call them “Winter Meadowhawks.”

The last two photos show the same male, perching on different surfaces. My guess is he was looking for a good source of thermal energy on a cool, windy day.

The Sun is always low in the sky during winter, even at its maximum altitude. Indirect incoming solar radiation (insolation) is less intense than direct insolation. The last photo shows the male dragonfly perched on a south-facing wooden board that is perpendicular to the surface of the Earth, therefore the solar energy received by the board is more intense than the energy received by the ground. This probably explains why the male moved from the ground to the board.

Enrichment

The last photo was taken on 01 December 2017 at 11:33:50 a.m. EST, as shown by the EXIF information for the image. The altitude of the Sun was 28.9° at 11:30 a.m., meaning a ray of sunlight formed an angle of 28.9° with horizontal surfaces such as the ground. At the same time, a ray of sunlight formed an angle of 61.1° with vertical surfaces such as the wooden board shown in the first and last photos. That’s the beauty of mathematics — some simple geometry shows clearly which surface received more intense insolation. Smart dragonflies!

Related Resource: Sun or Moon Altitude/Azimuth Table, U.S. Naval Observatory.

Copyright © 2017 Walter Sanford. All rights reserved.

The Road Taken

November 14, 2017

Two ruts converged in a yellow wood,
And sorry I could not travel both
And be one traveler, long I stood
And looked down one as far as I could
To where it bent in the undergrowth…

With sincere apologies to Robert Frost for slight modification of the title and first stanza of his famous poem The Road Not Taken in order to convey my impressions of Fall 2017 at Occoquan Bay National Wildlife Refuge.

Tech Tip: I used my Panasonic Lumix DMC-ZS150 superzoom camera to shoot the landscape photo featured in this blog post. The camera was set for manual focus at the hyperfocal distance for an aperture of f/4, based upon the instructions provided in the excellent video tutorial by Graham Houghton, “Panasonic Lumix FZ camera easier manual focus method — super point-and-shoot tip.”

Copyright © 2017 Walter Sanford. All rights reserved.

Confused by mild fall weather

November 12, 2017

A frog-let/toad-let — my term for small frogs and toads — was spotted during a photowalk along Easy Road at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA. Turns out it’s a Spring Peeper (Pseudacris crucifer), as indicated by the dark “X” on the frog’s dorsal side.

Every spring, the sound of male Spring Peepers calling for mates is deafening. You hear them, but you see them rarely. You don’t expect to see them during the second week in November!

Some amphibians have been confused by the mild weather in Northern Virginia, thinking it’s spring. The first hard freeze this fall occurred overnight on Friday-Saturday, November 10-11, when the record-setting low temperature at Reagan National Airport (DCA) was 26°F. I hope this little one hunkered down like frogs are supposed to when it’s cold.

Related Resource: Spring Peepers, a blog post by Alonso Abugattas, Natural Resources Manager for Arlington County Parks, Virginia USA.

Copyright © 2017 Walter Sanford. All rights reserved.

New HMP Weather Station

December 10, 2016

Did you notice the new automated weather station located in the central wetland area at Huntley Meadows Park, Fairfax County, Virginia USA?

The new automated weather station located in the central wetland area at Huntley Meadows Park, Fairfax County, Virginia USA.

13 NOV 2016 | Huntley Meadows Park | new automated weather station

The old weather station, installed and maintained by Virginia Tech University, went offline after 23 September 2016.

The [old] Huntley Meadows weather station was installed to help park personnel manage water levels within the wetland. Source Credit: Huntley Meadows Wetlands Research.

The new station is up-and-running; real-time data is supposed to be available online soon.

The new automated weather station located in the central wetland area at Huntley Meadows Park, Fairfax County, Virginia USA.

13 NOV 2016 | Huntley Meadows Park | new automated weather station

Editor’s Note: The author contacted both the park manager and the natural resource manager; neither person was willing to estimate when the new weather station will go online. Look for a post update when more information is available.

Copyright © 2016 Walter Sanford. All rights reserved.

Snowy scenes along the Hike-Bike Trail

February 7, 2016

The “exposure triangle” has three corners: 1) Aperture; 2) Shutter Speed; and 3) ISO (light sensitivity). When shooting in “Program” mode and Auto ISO, all three corners of the exposure triangle are wildcards set by the camera. In “Aperture Priority” mode and Auto ISO, the user selects the aperture (lens opening) and the camera selects the shutter speed and ISO. In “Shutter Priority” mode and Auto ISO, the user selects the shutter speed and the camera selects the aperture (lens opening) and ISO. Finally, in “Manual” mode the user selects all three settings in the exposure triangle.

All of the photos in this post were shot in “Aperture Priority” mode at ISO 100. That leaves one corner of the exposure triangle for the camera to set: Shutter Speed. At an aperture of f/4 and ISO 100, the camera is set for a relatively wide lens opening and maximum light sensitivity. Ice and snow are very reflective surfaces, so it’s no surprise the camera selected fast shutter speeds to limit the amount of light received by the camera sensor. One upside of this combination of settings: Camera shake was virtually a non-factor!

The following gallery of photos shows views along the Hike-Bike Trail at Huntley Meadows Park, a little more than a week after the “Blizzard of 2016.”

The view along the Hike-Bike Trail at Huntley Meadows Park, Fairfax County, Virginia USA.

4mm (25mm, 35mm equivalent) | f/4 | 1/2000s | ISO 100 | -1 ev

Notice that exposure compensation (ev) was used for most of the photos. In “Aperture Priority” mode at a fixed ISO, exposure compensation affects shutter speed: negative exposure values (ev) make the shutter speed faster, further reducing the amount of light received by the camera sensor; positive exposure values make the shutter speed slower, increasing the amount of light received.

Looking downstream along a creek that crosses the Hike-Bike Trail.

Looking downstream along a creek that crosses the Hike-Bike Trail at Huntley Meadows Park, Fairfax County, Virginia USA.

4mm | f/4 | 1/1000s | ISO 100 | -1 ev

Approaching the observation platform at the terminus of the Hike-Bike Trail. Notice the chromatic aberration in the tree tops at the upper-right corner of the photo.

Looking toward the observation platform at the terminus of the Hike-Bike Trail, Huntley Meadows Park, Fairfax County, Virginia USA.

4mm | f/4 | 1/1600s | ISO 100 | -1 ev

Looking toward the observation platform.

Approaching the observation platform at the terminus of the Hike-Bike Trail, Huntley Meadows Park, Fairfax County, Virginia USA.

4mm | f/4 | 1/1300s | ISO 100 | 0 ev

The central wetland area, as viewed from the observation platform. Notice the observation tower is faintly visible at the far side of the wetlands.

The central wetland area, as viewed from the observation platform at the terminus of the Hike-Bike Trail, Huntley Meadows Park, Fairfax County, Virginia USA.

4mm | f/4 | 1/2000s | ISO 100 | -1 ev

A vernal pool located near the terminus of the Hike-Bike Trail. The pool is mostly covered by ice and snow and somewhat difficult to see in the following photo.

A vernal pool located near the terminus of the Hike-Bike Trail at Huntley Meadows Park, Fairfax County, Virginia USA.

4mm | f/4 | 1/2000s | ISO 100 | -1 ev

A view of the “Mystery Pool.”

A view of the "Mystery Pool," Huntley Meadows Park, Fairfax County, Virginia USA.

4mm | f/4 | 1/1600s | ISO 100 | -1 ev

Heading toward the parking lot at the beginning of the Hike-Bike Trail.

The view along the Hike-Bike Trail at Huntley Meadows Park, Fairfax County, Virginia USA.

4mm | f/4 | 1/500s | ISO 100 | 0 ev

Related Resource: The exposure triangle and exposure compensation.

Copyright © 2016 Walter Sanford. All rights reserved.

Wild Turkey tracks

February 5, 2016

Pattern recognition. The richness of my field experience is often the result of my ability to recognize patterns in nature. For example, while exploring a remote location in the forest at Huntley Meadows Park, I spotted a set of Wild Turkey tracks (Meleagris gallopavo).

I recognized the shape of the turkey footprints in snow as a result of a chance encounter a few years ago, when I was able to tag along with Mr. Kevin Walter — Natural Resource Specialist, U.S. Army Garrison Fort Belvoir — for part of a field survey of birds at Accotink Bay Wildlife Refuge. As we were walking along “Great Blue Heron Trail,” Kevin pointed out a fresh set of Wild Turkey tracks.

Wild Turkey tracks (Meleagris gallopavo) spotted at Huntley Meadows Park, Fairfax County, Virginia USA.

01 FEB 2016 | Huntley Meadows Park | Wild Turkey track

Related Resource: Wild Turkey tracks, one of over 700 spottings by Geodialist on Project Noah. [Note: “Geodialist” is my username on Project Noah.]

Editor’s Note: Sincere thanks to Alonso Abugattas, Ed Eder, and Ben Jessup — a professional naturalist and two excellent amateur naturalists, respectively — for verifying my tentative field identification.

Copyright © 2016 Walter Sanford. All rights reserved.

HMP automated weather station

February 3, 2016

The following photos show the automated weather station located in the central wetland area at Huntley Meadows Park (HMP), Fairfax County, Virginia USA.

An annotated photograph of the weather station features labels for most of the instruments. The tipping bucket rain gauge is shown in the preceding photo, near the left side of the image; the rain gauge is one of several sensors not shown in the annotated photo provided by Virginia Tech University.

The following real-time data is available online: air temperature; wind direction and speed; and current water surface elevation.

Weather_Eng

(sample graphic image)

Air temperature is of particular interest to odonate hunters. 70°F is widely believed to be the minimum body temperature necessary for dragonfly flight. That is, for most species of dragonflies. Autumn Meadowhawk (Sympetrum vicinum) has been observed in flight at temperatures as low as 50°F!

Current water surface elevation may be the most challenging observation to interpret. Two known values help to put the measurement into context: the elevation of the berm is 34.5 feet; the bottom of the concrete box/culvert that serves as the outlet for the wetland is 32 feet. The water level may be higher than 34.5 feet when water breaches the berm. The water level may be lower than 32 feet when evapotranspiration exceeds inflow (precipitation and runoff).

Archived data: See a graph of hourly air temperature for the past two days.

Mean_Temp

(sample graphic image)

Archived data: See a graph of daily precipitation totals for the past month.

Rainfall

(sample graphic image)

Related Resource: My photoblog features a link from the right sidebar to the HMP Weather Station, where the reader will find quick links to all of the resources featured in this post.

Copyright © 2016 Walter Sanford. All rights reserved.

Splish Splash, I was takin’ a bath

July 23, 2014

The following photos show an Eastern Box Turtle (Terrapene carolina carolina) spotted on 22 July 2014 during a photowalk along a small creek that flows through the forest at Huntley Meadows Park.

They are found in most open forested habitats with lots of cover. They seek damp mud or pools when temperatures get too high. Source Credit: Virginia Herpetological Society.

The high temperature was 88°F (31°C), recorded at 3:05 p.m.

Eastern Box Turtle (Terrapene carolina carolina)

Eastern Box Turtle (Terrapene carolina carolina)

Eastern Box Turtle (Terrapene carolina carolina)

Editor’s Note:Splish Splash” is a song performed by Bobby Darin, recorded and released in 1958.

Copyright © 2014 Walter Sanford. All rights reserved.

The End

December 2, 2013

Sadly …

This is the end
Beautiful friend
This is the end
My only friend, the end.
The End, by The Doors

Late-fall/early winter is the end of dragonfly season in the mid-Atlantic region and literally the end for a couple of dead Autumn Meadowhawk dragonflies (Sympetrum vicinum) spotted at Huntley Meadows Park on 15 November 2013. Both carcasses were located along the boardwalk, under a canopy of trees near the observation tower.

The author is unable to identify either the gender or the cause of death for the first individual, lying ventral side up (shown below). At least two scenarios are possible. 1) The dragonfly died of natural cause(s) and was partially eaten afterward. 2) The dragonfly was killed by a predator, most likely a bird, since no other adult dragonfly species are on the wing in mid-November.

Autumn Meadowhawk dragonfly (carcass)

Photo 1. Autumn Meadowhawk dragonfly (carcass, gender unknown).

The second individual (shown below) is a male, as indicated by its coloration and terminal appendages. The carcass looks desiccated, like the dragonfly was freeze-dried. Mike Powell, a fellow wildlife photographer and blogger, observed frost on the boardwalk during the early morning on the 15th.

Autumn Meadowhawk dragonfly (male, carcass)

Photo 2. Autumn Meadowhawk dragonfly (carcass, male).

Copyright © 2013 Walter Sanford. All rights reserved.


%d bloggers like this: