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Abstract
An investigation of sensible and latent heat fluxes and their relation to synoptic weather events was performed using hourly meteorological measurements from National Data Buoy Center buoy 45003, located in northern Lake Huron, during April–November of 1984. Two temporal heat flux regimes were found to exist over Lake Huron. The first period extended from April through July and was characterized by periods of modest negative (downward) heat fluxes. The second regime was marked by periods of large positive (upward) heat fluxes and occurred from August through November. This later period accounted for 95%–100% of both the total positive sensible and latent heat fluxes. In addition, a comparison of the seasonal evolution of sensible and latent heat fluxes showed the transition from the negative to the positive flux regime occurred 10–20 days earlier for latent heat flux than for sensible heat flux. A notable, statistically significant increase of the surface heat flux variability from the negative to positive flux regimes with a general decrease in the near-surface atmospheric stability during the positive flux regime was found. During both flux regimes, the magnitude of surface sensible and latent heat fluxes remained coupled to transient synoptic-scale weather events. On average, the occurrences of minimum (maximum) heat fluxes preceded time periods of low (high) sea level pressure by 0–3 h during the negative flux regime. For the positive flux regime, maximum (minimum) surface heat fluxes followed the passage of low (high) pressure by approximately 24 h. In addition, maximum (minimum) sensible and latent heat fluxes preceded synoptic high (low) pressure by approximately 16 h. Typical synoptic surface weather patterns were identified for both significant positive and negative heat flux events, time periods when the atmosphere–lake heat exchange was maximized.
Abstract
An investigation of sensible and latent heat fluxes and their relation to synoptic weather events was performed using hourly meteorological measurements from National Data Buoy Center buoy 45003, located in northern Lake Huron, during April–November of 1984. Two temporal heat flux regimes were found to exist over Lake Huron. The first period extended from April through July and was characterized by periods of modest negative (downward) heat fluxes. The second regime was marked by periods of large positive (upward) heat fluxes and occurred from August through November. This later period accounted for 95%–100% of both the total positive sensible and latent heat fluxes. In addition, a comparison of the seasonal evolution of sensible and latent heat fluxes showed the transition from the negative to the positive flux regime occurred 10–20 days earlier for latent heat flux than for sensible heat flux. A notable, statistically significant increase of the surface heat flux variability from the negative to positive flux regimes with a general decrease in the near-surface atmospheric stability during the positive flux regime was found. During both flux regimes, the magnitude of surface sensible and latent heat fluxes remained coupled to transient synoptic-scale weather events. On average, the occurrences of minimum (maximum) heat fluxes preceded time periods of low (high) sea level pressure by 0–3 h during the negative flux regime. For the positive flux regime, maximum (minimum) surface heat fluxes followed the passage of low (high) pressure by approximately 24 h. In addition, maximum (minimum) sensible and latent heat fluxes preceded synoptic high (low) pressure by approximately 16 h. Typical synoptic surface weather patterns were identified for both significant positive and negative heat flux events, time periods when the atmosphere–lake heat exchange was maximized.
Abstract
Daily extreme precipitation events, exceeding a threshold for a 1-in-5-yr occurrence, were identified from a network of 935 Cooperative Observer stations for the period of 1908–2009. Each event was assigned a meteorological cause, categorized as extratropical cyclone near a front (FRT), extratropical cyclone near center of low (ETC), tropical cyclone (TC), mesoscale convective system (MCS), air mass (isolated) convection (AMC), North American monsoon (NAM), and upslope flow (USF). The percentage of events ascribed to each cause were 54% for FRT, 24% for ETC, 13% for TC, 5% for MCS, 3% for NAM, 1% for AMC, and 0.1% for USF. On a national scale, there are upward trends in events associated with fronts and tropical cyclones, but no trends for other meteorological causes. On a regional scale, statistically significant upward trends in the frontal category are found in five of the nine regions. For ETCs, there are statistically significant upward trends in the Northeast and east north central. For the NAM category, the trend in the West is upward. The central region has seen an upward trend in events caused by TCs.
Abstract
Daily extreme precipitation events, exceeding a threshold for a 1-in-5-yr occurrence, were identified from a network of 935 Cooperative Observer stations for the period of 1908–2009. Each event was assigned a meteorological cause, categorized as extratropical cyclone near a front (FRT), extratropical cyclone near center of low (ETC), tropical cyclone (TC), mesoscale convective system (MCS), air mass (isolated) convection (AMC), North American monsoon (NAM), and upslope flow (USF). The percentage of events ascribed to each cause were 54% for FRT, 24% for ETC, 13% for TC, 5% for MCS, 3% for NAM, 1% for AMC, and 0.1% for USF. On a national scale, there are upward trends in events associated with fronts and tropical cyclones, but no trends for other meteorological causes. On a regional scale, statistically significant upward trends in the frontal category are found in five of the nine regions. For ETCs, there are statistically significant upward trends in the Northeast and east north central. For the NAM category, the trend in the West is upward. The central region has seen an upward trend in events caused by TCs.
