Air-ground temperature exchange

<p>Most borehole paleoclimate studies have been based on the assumption that the exchange of temperature between the air and ground surface remains constant. However, secular changes in boundary-layer factors can generate anomalous ground temperatures. This dissertation is an investigation of factors that cause separation of air and ground temperatures on a seasonal to inter-annual time scale, including snow cover duration, latent energy of ground freezing, daily sunlight, precipitation, and vegetation. </p><p>Continual records of surface air and near-surface ground temperatures from five sites in North Dakota show similar trends in seasonal air-ground temperature separation. Statistical regressions of mean annual ground temperatures from Fargo and Bottineau sites indicate respective warming trends of 0.93±.09°C / 9 years and 1.17±.15°C / 6 years. Mean annual air temperatures and ground temperatures calculated with a conduction model assuming direct air-ground coupling do not display any significant trends. </p><p>The effect of snow cover duration on air-ground temperature exchange was tested by comparing average winter air-ground temperature differences (T5cm - Tair) with annual duration of snow cover. The correlation coefficients between these variables are: Bottineau: r2 = .84 (6 years), Fargo: r2 = .71 (9 years), Langdon: r2 = .56 (6 years), Minot: r2 = .79 (6 years), and Streeter: r2 = .87 (6 years). Best-fit latent energy of ground freezing values were determined with a conduction model and compared with total fall precipitation. The correlation coefficients between these variables are: Bottineau: r2= .38, Fargo r2= .66, Langdon: r2= .69, Minot: r2= .95, and Streeter: r2= .01. </p><p>A least-squares linear regression of mean annual air temperatures recorded in northwestern North Dakota from 1895 to 1995 indicates a warming magnitude of 1.57±.23°C per century. This temperature time series was forced into the ground with direct coupling to generate a synthetic temperature-depth profile. Inversion of this profile yielded a ground-surface warming magnitude of 1.7°C per century. Total fall precipitation is used as a proxy for latent energy of ground freezing. Latent energy effects were modeled with direct coupling of the regional air temperature record and a temperature dependent constraint for snow cover insulation. This generated a 0.4°C per century signal. </p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Geology

Year

2000

Author dc:creator

• Schmidt, William L.

Contributors dc:contributor

• W.D. Gosnold Jr.

• Earth temperature--North Dakota; Soil temperature--North Dakota; Climatic changes--North Dakota; Global warming
• Geology

Repository record dc:identifier

https://commons.und.edu/theses/264

OAI identifier oai:identifier

oai:commons.und.edu:theses-1263