An Evaluation of January Temperature Anomalies in the United States Utilizing  a Synoptic Climatolog...
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An Evaluation of January Temperature Anomalies in the United States Utilizing a Synoptic Climatological Approach. Department of Geography, University of Delaware Center for Climatic Research Melissa Malin Dr. Katrina Frank Steven Quiring Dr. Laurence Kalkstein. 85 th AMS Annual Meeting

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An Evaluation of January Temperature Anomalies in the United States Utilizing a Synoptic Climatological Approach

Department of Geography, University of Delaware

Center for Climatic Research

Melissa Malin

Dr. Katrina Frank

Steven Quiring

Dr. Laurence Kalkstein

85th AMS Annual Meeting

January 15, 2005


The January Thaw States Utilizing a Synoptic Climatological Approach

has roots in New England weather folklore

“…a characteristic meteorological condition that tends to occur on or near a specific calendar date.” -American Meteorological Society

an anomalous warm spell invading during the coldest time of year


i. States Utilizing a Synoptic Climatological Approachidentification of a January Thaw signal across the United States

ii. assess the inter- and intra- regional variability of the January Thaw

Can the Thaw be explained synoptically? …through an assessment of air mass frequency

The Goals Of This Investigation....


US Regions States Utilizing a Synoptic Climatological Approach

West

Mountain

East

Great Plains

Midwest


Weather Data States Utilizing a Synoptic Climatological Approach

National Climatic Data Center

twice daily

4 a.m. & 4 p.m.

Air Temperature

Dew Point Temperature

Air Mass Data

Spatial Synoptic Classification

daily

Dry Moderate Dry Moderate +

Dry Polar Dry Polar -

Dry Tropical Moist Polar +

Moist Moderate

Moist Polar

Moist Tropical

Transition

1948 – 2001

December 1 – February 28

Data


Philadelphia, Pennsylvania States Utilizing a Synoptic Climatological Approach

average daily temperatures plotted at each station

Methods and Analysis

  • standardized using a five-day moving window

  • identified by date of the third day


The identification of singularities

Philadelphia, Pennsylvania States Utilizing a Synoptic Climatological Approach

Upper Bound

Winter Trendline

Lower Bound

the identification of singularities

singularity at

January 24 -25

  • a second-order polynomial curve fit for winter trendline

  • upper/ lower bounds set at two standard deviations


Cheyenne, Wyoming States Utilizing a Synoptic Climatological Approach

(Thaw)

December 3

Upper Bound

(Thaw)

January 16 - 18

Winter Trendline

Lower Bound

(Freeze)

January 2 - 4

the identification of singularities

an example of singularities found at a mountain region station


Synoptic analysis
synoptic analysis States Utilizing a Synoptic Climatological Approach

Three techniques were used to detect changes in air mass frequency during Thaw and Freeze events.

Linear Method

Second-order Method

Mean Method


Linear method

Philadelphia, Pennsylvania States Utilizing a Synoptic Climatological Approach

linear method

  • useful for air masses that exhibit a general frequency trend across a season and for stations with winter seasons that extend beyond the period examined here


Philadelphia, Pennsylvania States Utilizing a Synoptic Climatological Approach

second-order method

  • useful for air masses that do not display such general, linear frequency tendencies and may be less (more) frequent in early and late winter though more (less) prominent throughout the middle of the season


mean method States Utilizing a Synoptic Climatological Approach

Station Thaw Observed DM Frequency DM Monthly Mean Frequency

PHL 24 Jan 22.5% 21.5%

PWM 23 Jan 16.0% 14.5%

PVD 23 Jan 20.8% 19.8%

RIC 24 Jan 25.5% 26.5%

SYR 24 Jan 11.6% 10.5%

  • useful here because singularity windows are scrutinized with only frequencies typical of that month and seasonal trends do not contribute to calculating the strength of that departure


Finding correlations between temperature differences and frequency differences
finding correlations between temperature differences and frequency differences

Eastern Region Thaws and Linear Method Output


14-17 January frequency differences

15-17 January

26-29 December

22-24 January

14-16 January

23-26 January

15–17 January

24-25 January

29 December

Results

Inter- and Intra-Regional Variability of the Thaw

  • found rather cohesive January thaw signal in every region

  • appears to move somewhat systematically across the country


Found less cohesive january freeze signal in western us
found less cohesive frequency differencesJanuary Freeze signal in western US

28-29 January

(all stations)

5-8 January

26-28 January

4 January

3-4 January

1 January

2-7 January

Results

Inter- and Intra-Regional Variability of the Freeze

  • appears to also progress somewhat systematically eastward


Results of Synoptic Analysis.... frequency differences

January Thaw

It appears there is no single synoptic explanation for the Thaw across the country.

East and West …..

No Relationships

Mountain…….

Significantly more frequent warm air masses (all)

Significantly less frequent cold air masses (L,M)

Great Plains……….

Significantly less frequent DP- (S)

Significantly more frequent DP (S)

Midwest…………

Significantly more frequent MT (all)

Significantly less frequent DT (all)


Results of Synoptic Analysis.... frequency differences

January Freeze

It appears there is no single synoptic explanation for the Freeze across the country.

West ……….

Significantly less frequent warm air masses (all)

Significantly more frequent MP (L,S)

Mountain………

Significantly more frequent DP- (L)

Significantly more frequent MP (M)

Great Plains……

Significantly more frequent DP- (all)

Significantly less frequent DP (all)

Significantly more frequent DT* (all)


Conclusions frequency differences

this research provides evidence for the existence of a regionally coherent January Thaw and January Freeze

both show signs of west- east advancement across the US

The Freeze often occurs just prior to the Thaw

the Thaw and Freeze are related to variable synoptic conditions rather than a single air mass type

most conditions observed are generally intuitive

the relationship between synoptic conditions and singularities is most apparent in the Central US

the air mass-based methodologies used here did not detect a cause for the Thaw in the East

this needs further investigation…


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