Anomalous temperature
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Anomalous Temperature: Impacts and Mechanisms
Anomalous Temperature Regimes in the Southeastern United States
Anomalous temperature regimes (ATRs), including cold-air outbreaks (CAOs) and warm waves (WWs), significantly impact the southeastern United States during winter. These events are characterized by distinct synoptic behaviors and are influenced by low-frequency atmospheric modes. During CAOs, negative geopotential height anomalies in the upper troposphere over the Southeast and positive anomalies in the lower troposphere over the central United States are observed. Conversely, WWs exhibit opposite patterns. These anomalies create surface east-west geopotential height dipoles, leading to northerly or southerly flows that result in cold or warm surface air temperature anomalies, respectively .
Long-Term Trends and Modulation by Low-Frequency Modes
Analysis of ATRs from 1949 to 2011 reveals no significant long-term trends in the frequency of CAOs or WWs across the continental United States. However, interannual variability is influenced by low-frequency modes such as the North Atlantic Oscillation (NAO) and the Pacific-North American (PNA) pattern. CAOs in the Southeast are modulated by the NAO, while WWs in the eastern and southern United States are influenced by a combination of the NAO, PNA, Pacific Decadal Oscillation (PDO), and El Niño-Southern Oscillation (ENSO) .
Impacts on Human Health and Safety
Anomalous temperatures have profound effects on human health and safety. For instance, a study spanning 38 years (1980-2017) in the contiguous USA found that anomalously warm years, as projected under the Paris Climate Agreement, could lead to an estimated 1,601 additional injury deaths, predominantly among males aged adolescence to middle age. These deaths are primarily due to increases in drownings, transport accidents, assaults, and suicides, highlighting the need for targeted interventions during periods of anomalously warm temperatures .
Effects on Marine Life and Ecosystems
Anomalous temperatures also disrupt marine ecosystems. For example, the 2014-2015 warming anomaly in the Southern California Current System, observed through underwater gliders, resulted in the highest regional upper ocean temperature anomalies since 2006. This warming led to a depressed thermocline, high stratification, and changes in the vertical distribution of chlorophyll fluorescence, indicating significant biological consequences .
Reproductive Activity in Fish
In fish, anomalous temperatures can severely impact reproductive activities. Studies on the grass puffer (Takifugu alboplumbeus) show that both high (28°C) and low (14°C) temperatures suppress the expression of genes involved in the reproductive neuroendocrine system, including gonadotropin-releasing hormone (GnRH), kisspeptin, and gonadotropin-inhibitory hormone (GnIH). This suppression leads to decreased levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and growth hormone (GH), ultimately terminating reproductive activities .
Anomalous Winter Temperature and Precipitation in Southern China
In southern China, anomalous low-temperature and high-precipitation events during winter are influenced by atmospheric circulation patterns. Strong Siberian High (SBH), East Asian trough (EAT), and East Asian jet stream (EAJS) are conducive to low temperatures, while anomalous southerly flows and weak EAT at 500 hPa contribute to increased precipitation. These patterns are further modulated by ENSO events, with more precipitation during El Niño winters and less during La Niña winters .
Conclusion
Anomalous temperature events have wide-ranging impacts on both human and ecological systems. Understanding the synoptic behaviors, long-term trends, and modulation by low-frequency modes is crucial for predicting and mitigating these effects. As global temperatures continue to rise, the frequency and intensity of these anomalous events are likely to increase, necessitating proactive measures to protect vulnerable populations and ecosystems.
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