Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Extremely poor conditions??
    From: Marcel Tschudin
    Date: 2012 Mar 21, 10:51 +0200
    Looking at the sounding data (72645 GRB Green Bay) from Mar 17 00Z to Mar 19 00Z shows:

    -> Over this period the air temperature is fairly constant (around 18°C to 20°C) at altitudes around 600m to 700m. Compare this temperature with the Sea *Surface* Temperature (SST).

    -> The 12Z soundings show strong inversions, especially the one of Mar 18 with +7.8° per 330m (corresponding to +24°C/km) but also the one of Mar 17 with +3.8°C per 470m (corresponding to +8°/km). (Note: The 12Z soundings contain at least partially still some parts of the normal morning inversions; the 00Z data show the temperature decreasing normally with increasing altitude.) Compare these temperature gradients with the "normal" one of -6°C/km to -7°C/km producing "normal refraction".

    -> Further: "I did take a walk to the end of the pier, and the air temperature 7-13 feet above the water level dropped by at least 15 F" suggests strong temperature variations near the surface, thus indicating a non-stratified temperature distribution which results in an optically unstable atmosphere.

    => I think there is sufficient evidence of abnormal atmospheric conditions.

    Regarding the normal morning inversions (this is not related to the discussed observations): I would expect them to produce a systematic refraction bias (error) when measuring shortly after sun rise from the shore altitudes relative to the sea horizon. It would be interesting to estimate the size of this bias from measurements. I expect this error to be negligible for measurements at sea but larger for measurements made further inland.


    On Wed, Mar 21, 2012 at 6:33 AM, bill <billyrem42---.net> wrote:

    This is the Bill of the Alex and Bill refraction show. I have neither the training or mental horsepower to explain what we observed, but can provide more details for those interested.

    Before the details, I would urge you to get an overview by visiting:

    Under Michigan, click on surface temps and run the animation.

    Then, use Google Earth and fly to N 42d 06!891, W 86d 29.301
    The coordinates were taken from my GPS.  Google Earth shows our location approximately 15'NNW of our true location. This will give you a birds-eye view of the wide range/smorgasbord of possible temperatures within a 1500' radius.

    As an overview, this area has been setting record highs for over a week  (this winter!), as well as record high lows. Low to mid 80's F, 20 F or more over normal. (It is not unusual to have snow on the ground on Easter.)

    The southern end of Lake Michigan is the shallow end (often 60-30 feet under the boat well offshore. Being shallow and and 307 miles south of the north end, it warms up faster.

    Drilling down, according to the first URL above, surface temperatures offshore (5 or more miles) were in the 44-45F range on the 17th .Sub surface temps (10 meters) were almost uniform for the lake at 40 F, with a few isolated cooler spikes. As the day wore on, near shore surface temperatures on the south-eastern side (our location) of the lake exceeded 50F.

    Regarding our observation location, it was at very least interesting. We were on the north concrete pier/breakwater perhaps 15 feet from the dredged channel which ran out to the lake at approx 290d.  Sand behind us, sand along side us to the north, and sand running west along the north side of the pier about 500 feet to the beach. Across the channel, a beach about 500 feet to the east of us. Throw in an asphalt parking lot about 150 feet north of us. I would love to see a aerial thermal 1500' radius image of our location. I imagine it would look like a Leroy Neiman lithograph.

    The wind was approx. 8 kt out of the SSW and parallel to the shore (based on my observations of kites flying). Given the short fetch there was little wave action, or opportunity to churn the water.

    I did take a walk to the end of the pier, and the air temperature 7-13 feet above the water level dropped by at least 15 F. A graphic description:  People on the beach in swimwear, walkers in shorts and T-shirts. Folks fishing or lingering on the pier in jeans and hooded sweatshirts.

    Sadly our off-shore buoys (45002 and 45007) are still decommissioned for winter, so I could not obtain air temperatures 4 meters off the surface.

    The Green Bay, Wisconsin station

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site