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Scott Curtis and Robert Adler

Abstract

In this study, gridded observed precipitation datasets are used to construct rainfall-based ENSO indices. The monthly El Niño and La Niña indices (EI and LI) measure the steepest zonal gradient of precipitation anomalies between the equatorial Pacific and the Maritime Continent. This is accomplished by spatially averaging precipitation anomalies using a spatial boxcar filter, finding the maximum and minimum averages within a Pacific and Maritime Continent domain for each month, and taking differences. The EI and LI can be examined separately or combined to produce one El Niño–Southern Oscillation (ENSO) precipitation index (ESPI). ESPI is well correlated with traditional sea surface temperature (e.g., Niño-3.4) and pressure indices [e.g., Southern Oscillation index (SOI)], leading Niño-3.4 by a month. ESPI has a tendency to produce stronger La Niñas than does Niño-3.4 and SOI. One advantage satellite-derived precipitation indices have over more conventional indices is describing the strength and position of the Walker circulation. Examples are given of tracking the impact of recent ENSO events on the tropical precipitation fields. The 1982/83 and 1997/98 events were unique in that, during the transition from the warm to the cold phase, precipitation patterns associated with El Niño and La Niña were simultaneously strong. According to EI and ESPI, the 1997/98 El Niño was the strongest event over the past 20 years.

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Scott Curtis and Stefan Hastenrath

Abstract

Trends of circulation and climate in the equatorial Pacific during 1948–92 were analyzed from observations of sea surface temperature (T), cloudiness (C), sea level pressure (P), specific humidity (Q), and zonal wind component. From indices compiled for the cold tongue in the east, the central equatorial Pacific, the warm pool in the west, and the eastern equatorial Indian Ocean, interannual relationships were compared with long-term trends. On the interannual timescale the significant negative T–P correlations in the eastern Pacific indicate a hydrostatic forcing of T on P, and the negative P–C correlations in the western Pacific and eastern Indian Oceans are consistent with anomalously high P through subsidence favoring clear sky. The tropical Pacific is warming and most markedly in the east; there is a weakening of the westward pressure gradient; and increasing Q and C in the east. Warming in the eastern section of the basin may force falling pressure hydrostatically, the trend of P being largest near 155°W. In the domain 155°–90°W easterlies accelerate, favoring enhanced evaporation and humidity. The strengthening of the winds east of 155°W and slowdown to the west imply enhanced convergence and upward motion, consistent with increasing C near 155°W. Also warming may thermodynamically force increasing humidity and cloudiness in the realm of the intertropical convergence zone. The observed basin-wide warming and weakening of the westward pressure gradient, with the consequent slackening of easterlies over the central equatorial Pacific, reflect a tendency toward patterns characteristic of the low/warm phase of the Southern Oscillation.

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Scott Curtis, Patrick Long, and Jennifer Arrigo

Abstract

No abstract available.

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Scott Curtis, Douglas W. Gamble, and Jeff Popke

Abstract

This study uses empirical models to examine the potential impact of climate change, based on a range of 100-yr phase 5 of the Coupled Model Intercomparison Project (CMIP5) projections, on crop water need in Jamaica. As expected, crop water need increases with rising temperature and decreasing precipitation, especially in May–July. Comparing the temperature and precipitation impacts on crop water need indicates that the 25th percentile of CMIP5 temperature change (moderate warming) yields a larger crop water deficit than the 75th percentile of CMIP5 precipitation change (wet winter and dry summer), but the 25th percentile of CMIP5 precipitation change (substantial drying) dominates the 75th percentile of CMIP5 temperature change (extreme warming). Over the annual cycle, the warming contributes to larger crop water deficits from November to April, while the drying has a greater influence from May to October. All experiments decrease crop suitability, with the largest impact from March to August.

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Robert Munroe, Burrell Montz, and Scott Curtis

Abstract

Storm surge has been identified as a dangerous and damaging coastal hazard that is expected to be exacerbated by rising sea levels. However, storm surge research and applications are relatively new and poorly understood compared to other storm-related hazards. This survey-based research of emergency support personnel across eastern North Carolina aims to connect ongoing research with the needs of storm surge users. Results indicate that emergency managers and other emergency support functions depend on storm surge information to assess and communicate risk, to educate the public, to evacuate the public, or for long-term resilience and recovery planning. They were generally satisfied with the type and timing of currently available surge information, but desired additional types of surge information (i.e., timing) and longer lead times.

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Theodore L. Allen, Scott Curtis, and Douglas W. Gamble

Abstract

The annual rainfall pattern of the intra-Americas sea reveals a bimodal feature with a minimum during the midsummer known as the midsummer dry spell (MSD). A first attempt is made to examine the impact of the MSD on vegetation through a normalized difference vegetation index (NDVI) analysis in Jamaica. Tropical Rainfall Measuring Mission rainfall estimates and NDVI derived from the Terra Moderate Resolution Imaging Spectroradiometer highlight a consistent MSD feature in both rainfall and vegetative vigor. Spatial variation of this MSD NDVI response is evident throughout Jamaica, with the strongest relationship between the rainfall reduction and NDVI decline throughout the southern portions of Jamaica including the area of major domestic food production. In all years except 2005 there is a notable reduction from early-summer NDVI to midsummer NDVI in this agricultural region. However, the lagged vegetative response undergoes clear interannual variation and is affected by other forcings besides rainfall, such as brush fires and extreme wind.

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Guojun Gu, Robert F. Adler, George J. Huffman, and Scott Curtis

Abstract

Global and large regional rainfall variations and possible long-term changes are examined using the 27-yr (1979–2005) Global Precipitation Climatology Project (GPCP) monthly dataset. Emphasis is placed on discriminating among variations due to ENSO, volcanic events, and possible long-term climate changes in the Tropics. Although the global linear change of precipitation in the dataset is near zero during the time period, an increase in tropical rainfall is noted in the dataset, with a weaker decrease over Northern Hemisphere middle latitudes. Focusing on the Tropics (25°S–25°N), the dataset indicates an upward linear change (0.06 mm day−1 decade−1) and a downward linear change (−0.01 mm day−1 decade−1) over tropical ocean and land, respectively. This corresponds to an about 5.5% increase (ocean) and 1% decrease (land) during the entire 27-yr time period. The year 2005 has the largest annual tropical total precipitation (land plus ocean) for the GPCP record. The five highest years are (in descending order) 2005, 2004, 1998, 2003, and 2002. For tropical ocean the five highest years are 1998, 2004, 2005, 2002, and 2003.

Techniques are applied to isolate and quantify variations due to ENSO and two major volcanic eruptions during the time period (El Chichón, March 1982; Mount Pinatubo, June 1991) in order to examine longer-time-scale changes. The ENSO events generally do not impact the tropical total rainfall, but rather induce significant anomalies with opposite signs over tropical land and ocean. The impact of the two volcanic eruptions is estimated to be about a 5% reduction in tropical rainfall over both land and ocean. A modified dataset (with ENSO and volcano effects removed) retains the same approximate linear change slopes, but with reduced variances, thereby increasing the statistical significance levels associated with the long-term rainfall changes in the Tropics. However, although care has been taken to ensure that this dataset is as homogeneous as possible, firm establishment of the existence of the discussed changes as long-term trends may require continued analysis of the input datasets and a lengthening of the observation period.

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Scott Curtis, Robert F. Adler, George J. Huffman, Guojun Gu, David T. Bolvin, and Eric J. Nelkin
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Minh D. Phan, Burrell E. Montz, Scott Curtis, and Thomas M. Rickenbach

Abstract

Millions of people in the United States regularly acquire information from weather forecasts for a wide variety of reasons. The rapid growth in mobile device technology has created a convenient means for people to retrieve this data, and in recent years, mobile weather applications (MWAs) have quickly gained popularity. Research on weather sources, however, has been unable to sufficiently capture the importance of this form of information gathering. As use of these apps continues to grow, it is important to gain insight on the usefulness of MWAs to consumers. To better examine MWA preferences and behaviors relating to acquired weather information, a survey of 308 undergraduate students from three different universities throughout the southeast United States was undertaken. Analyses of the survey showed that smartphone MWAs are the primary weather forecast source among college students. Additionally, MWA users tend to seek short-term forecast information, like the hourly forecast, from their apps. Results also provide insight into daily MWA use by college students as well as perceptions of and preferential choices for specific MWA features and designs. The information gathered from this study will allow other researchers to better evaluate and understand the changing landscape of weather information acquisition and how this relates to the uses, perceptions, and values people garner from forecasts. Organizations that provide weather forecasts have an ever-growing arsenal of resources to disseminate information, making research of this topic extremely valuable for future development of weather communication technology.

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Robert F. Adler, George J. Huffman, David T. Bolvin, Scott Curtis, and Eric J. Nelkin

Abstract

A technique is described to use Tropical Rainfall Measuring Mission (TRMM) combined radar–radiometer information to adjust geosynchronous infrared satellite data [the TRMM Adjusted Geostationary Operational Environmental Satellite Precipitation Index (AGPI)]. The AGPI is then merged with rain gauge information (mostly over land) to provide finescale (1° latitude × 1° longitude) pentad and monthly analyses, respectively. The TRMM merged estimates are 10% higher than those from the Global Precipitation Climatology Project (GPCP) when integrated over the tropical oceans (37°N–37°S) for 1998, with 20% differences noted in the most heavily raining areas. In the dry subtropics the TRMM values are smaller than the GPCP estimates. The TRMM merged product tropical-mean estimates for 1998 are 3.3 mm day−1 over ocean and 3.1 mm day−1 over land and ocean combined. Regional differences are noted between the western and eastern Pacific Ocean maxima when TRMM and GPCP are compared. In the eastern Pacific rain maximum the TRMM and GPCP mean values are nearly equal, which is very different from the other tropical rainy areas where TRMM merged product estimates are higher. This regional difference may indicate that TRMM is better at taking into account the vertical structure of the rain systems and the difference in structure between the western and eastern (shallower) Pacific convection.

Comparisons of these TRMM merged analysis estimates with surface datasets shows varied results; the bias is near zero when compared with western Pacific Ocean atoll rain gauge data, but is significantly positive as compared with Kwajalein radar estimates (adjusted by rain gauges). Over land the TRMM estimates also show a significant positive bias. The inclusion of gauge information in the final merged product significantly reduces the bias over land, as expected.

The monthly precipitation patterns produced by the TRMM merged data process clearly show the evolution of the El Niño–Southern Oscillation (ENSO) tropical precipitation pattern from early 1998 (El Niño) to early 1999 (La Niña) and beyond. The El Niño-minus-La Niña difference map shows the expected eastern Pacific maximum, the “Maritime Continent” minima, and other tropical and midlatitude features, very similar to those detected by the GPCP analyses. However, summing the El Niño-minus-La Niña differences over the global tropical oceans yields divergent answers for interannual changes from TRMM, GPCP, and other estimates. This emphasizes the need for additional validation and analysis before it is feasible to understand the relations between global precipitation anomalies and Pacific Ocean ENSO temperature changes.

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