Understanding Diurnal Variability of Precipitation through Observations and Models (UDVPOM)
Description:
The variability of precipitation is an immensely important subject because of its direct control on and response to the atmospheric and surface water-energy cycles, which strongly govern weather and climate. Precipitation variability takes place across the complete range of scales up to the very high local-diurnal scales down to the very low global-decadal and longer scales. The diurnal variability of precipitation is a multifaceted global phenomenon with embedded regional phenomena far more complex than can be readily explained with generalized causal factors. For example, the generally dominant late-night to early-morning oceanic rainfall peak is often accompanied by a secondary afternoon peak, while the generally dominant mid- to late-afternoon continental rainfall peak can be accompanied or even replaced by a secondary early-morning peak. Over the earth's many regions, there are a host of mechanisms at work in producing diurnal rainfall processes, no one of which can be used to explain the entire process. Instead, it appears that for a given region, a mixture of mechanisms are often at play, whose individual components control smaller-scale diurnal modes, ultimately working together to describe the mean global process. The topic of this special collection is the diurnal variability of precipitation, cast in the framework of "Understanding Diurnal Variability of Precipitation through Observations and Models" (UDVPOM). Since the advent of high-quality, multiyear, and globally distributed observations of precipitation from spaceborne sensors, there has yet to be a focused study concerning the topic of the diurnal variability of precipitation. This special collection of the Journal of Climate contains 11 papers that seek to bring about this focus. The full collection preface can be viewed here.
Collection coordinators:
Song Yang and Eric A. Smith
Understanding Diurnal Variability of Precipitation through Observations and Models (UDVPOM)
Abstract
The diurnal occurrence of warm-season rainfall over the U.S. mainland is examined, particularly in light of forcings at multiple scales. The analysis is based on a radar dataset of 12-seasons duration covering the U.S. mainland from the Continental Divide eastward. The dataset resolves 2-km features at 15-min intervals, thus providing a detailed view of both large- and regional-scale diurnal patterns, as well as the statistics of events underlying these patterns. The results confirm recent findings with respect to the role of propagating rainfall systems and the high frequency at which these are excited by sensible heating over elevated terrain. Between the Rockies and the Appalachians, ∼60% of midsummer rainfall occurs in this manner.
Most rainfall in the central United States is nocturnal and may be attributed to the following three main forcings: 1) the passage of eastward-propagating rainfall systems with origins near the Continental Divide at 105°W; 2) a nocturnal reversal of the mountain–plains solenoid, which is associated with widespread ascent over the plains; and 3) the transport of energetic air and moisture convergence by the Great Plains low-level jet.
Other features of interest include effects of the Appalachians, semidiurnal signals of regional significance, and the impact of breezes along the Gulf of Mexico. A modest effort was put forth to discern signals associated with El Niño and the Southern Oscillation. While tendencies in precipitation patterns are observed, the record is too short to draw conclusions of general significance.
Abstract
The diurnal occurrence of warm-season rainfall over the U.S. mainland is examined, particularly in light of forcings at multiple scales. The analysis is based on a radar dataset of 12-seasons duration covering the U.S. mainland from the Continental Divide eastward. The dataset resolves 2-km features at 15-min intervals, thus providing a detailed view of both large- and regional-scale diurnal patterns, as well as the statistics of events underlying these patterns. The results confirm recent findings with respect to the role of propagating rainfall systems and the high frequency at which these are excited by sensible heating over elevated terrain. Between the Rockies and the Appalachians, ∼60% of midsummer rainfall occurs in this manner.
Most rainfall in the central United States is nocturnal and may be attributed to the following three main forcings: 1) the passage of eastward-propagating rainfall systems with origins near the Continental Divide at 105°W; 2) a nocturnal reversal of the mountain–plains solenoid, which is associated with widespread ascent over the plains; and 3) the transport of energetic air and moisture convergence by the Great Plains low-level jet.
Other features of interest include effects of the Appalachians, semidiurnal signals of regional significance, and the impact of breezes along the Gulf of Mexico. A modest effort was put forth to discern signals associated with El Niño and the Southern Oscillation. While tendencies in precipitation patterns are observed, the record is too short to draw conclusions of general significance.
Abstract
Hourly or 3-hourly precipitation data from Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN) and Tropical Rainfall Measuring Mission (TRMM) 3B42 satellite products and rain gauge records are used to characterize East Asian summer monsoon rainfall, including spatial patterns in June–August (JJA) mean precipitation amount, frequency, and intensity, as well as the diurnal and semidiurnal cycles. The results show that the satellite products are comparable to rain gauge data in revealing the spatial patterns of JJA precipitation amount, frequency, and intensity, with pattern correlation coefficients for five subregions ranging from 0.66 to 0.94. The pattern correlation of rainfall amount is higher than that of frequency and intensity. Relative to PERSIANN, the TRMM product has a better resemblance with rain gauge observations in terms of both the pattern correlation and root-mean-square error. The satellite products overestimate rainfall frequency but underestimate its intensity. The diurnal (24 h) harmonic dominates subdaily variations of precipitation over most of eastern China. A late-afternoon maximum over southeastern and northeastern China and a near-midnight maximum over the eastern periphery of the Tibetan Plateau are seen in the rain gauge data. The diurnal phases of precipitation frequency and intensity are similar to those of rainfall amount in most regions, except for the middle Yangtze River valley. Both frequency and intensity contribute to the diurnal variation of rainfall amount over most of eastern China. The contribution of frequency to the diurnal cycle of rainfall amount is generally overestimated in both satellite products. Both satellite products capture well the nocturnal peak over the eastern periphery of the Tibetan Plateau and the late-afternoon peak in southern and northeastern China. Rain gauge data over the region between the Yangtze and Yellow Rivers show two peaks, with one in the early morning and the other later in the afternoon. The satellite products only capture the major late-afternoon peak.
Abstract
Hourly or 3-hourly precipitation data from Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN) and Tropical Rainfall Measuring Mission (TRMM) 3B42 satellite products and rain gauge records are used to characterize East Asian summer monsoon rainfall, including spatial patterns in June–August (JJA) mean precipitation amount, frequency, and intensity, as well as the diurnal and semidiurnal cycles. The results show that the satellite products are comparable to rain gauge data in revealing the spatial patterns of JJA precipitation amount, frequency, and intensity, with pattern correlation coefficients for five subregions ranging from 0.66 to 0.94. The pattern correlation of rainfall amount is higher than that of frequency and intensity. Relative to PERSIANN, the TRMM product has a better resemblance with rain gauge observations in terms of both the pattern correlation and root-mean-square error. The satellite products overestimate rainfall frequency but underestimate its intensity. The diurnal (24 h) harmonic dominates subdaily variations of precipitation over most of eastern China. A late-afternoon maximum over southeastern and northeastern China and a near-midnight maximum over the eastern periphery of the Tibetan Plateau are seen in the rain gauge data. The diurnal phases of precipitation frequency and intensity are similar to those of rainfall amount in most regions, except for the middle Yangtze River valley. Both frequency and intensity contribute to the diurnal variation of rainfall amount over most of eastern China. The contribution of frequency to the diurnal cycle of rainfall amount is generally overestimated in both satellite products. Both satellite products capture well the nocturnal peak over the eastern periphery of the Tibetan Plateau and the late-afternoon peak in southern and northeastern China. Rain gauge data over the region between the Yangtze and Yellow Rivers show two peaks, with one in the early morning and the other later in the afternoon. The satellite products only capture the major late-afternoon peak.
