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Carl J. Schreck III, Kenneth R. Knapp, and James P. Kossin

Abstract

Using the International Best Track Archive for Climate Stewardship (IBTrACS), the climatology of tropical cyclones is compared between two global best track datasets: 1) the World Meteorological Organization (WMO) subset of IBTrACS (IBTrACS-WMO) and 2) a combination of data from the National Hurricane Center and the Joint Typhoon Warning Center (NHC+JTWC). Comparing the climatologies between IBTrACS-WMO and NHC+JTWC highlights some of the heterogeneities inherent in these datasets for the period of global satellite coverage 1981–2010. The results demonstrate the sensitivity of these climatologies to the choice of best track dataset. Previous studies have examined best track heterogeneities in individual regions, usually the North Atlantic and west Pacific. This study puts those regional issues into their global context. The differences between NHC+JTWC and IBTrACS-WMO are greatest in the west Pacific, where the strongest storms are substantially weaker in IBTrACS-WMO. These disparities strongly affect the global measures of tropical cyclone activity because 30% of the world’s tropical cyclones form in the west Pacific. Because JTWC employs similar procedures throughout most of the globe, the comparisons in this study highlight differences between WMO agencies. For example, NHC+JTWC has more 96-kt (~49 m s−1) storms than IBTrACS-WMO in the west Pacific but fewer in the Australian region. This discrepancy probably points to differing operational procedures between the WMO agencies in the two regions. Without better documentation of historical analysis procedures, the only way to remedy these heterogeneities will be through systematic reanalysis.

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Michael J. Ventrice, Christopher D. Thorncroft, and Carl J. Schreck III

Abstract

High-amplitude convectively coupled equatorial atmospheric Kelvin waves (CCKWs) are explored over the tropical Atlantic during the boreal summer (1989–2009). Focus is given to the atmospheric environmental conditions that are important for tropical cyclogenesis.

CCKWs are characterized by deep westerly vertical wind shear to the east of its convectively active phase and easterly vertical wind shear to the west of it. This dynamical signature increases vertical wind shear over the western tropical Atlantic ahead of the convectively active phase, and reduces vertical wind shear after its passage. The opposite is true over the eastern tropical Atlantic where the climatological vertical wind shear is easterly.

Positive total column water vapor (TCWV) anomalies progress eastward with the convectively active phase of the CCKW, whereas negative TCWV anomalies progress eastward with the convectively suppressed phase. During the passage of the convectively active phase of the CCKW, a zonally oriented strip of low-level cyclonic relative vorticity is generated over the tropical Atlantic. Two days later, this strip becomes more wavelike and moves back toward the west. This signature resembles a train of westward-moving easterly waves and suggests CCKWs may influence such events.

Strong CCKWs over the tropical Atlantic tend to occur during the decay of the active convection associated with the Madden–Julian oscillation over the Pacific. This relationship could be used to provide better long-range forecasts of tropical convective patterns and Atlantic tropical cyclogenesis.

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Carl J. Schreck III, Lei Shi, James P. Kossin, and John J. Bates

Abstract

The Madden–Julian oscillation (MJO) and convectively coupled equatorial waves are the dominant modes of synoptic-to-subseasonal variability in the tropics. These systems have frequently been examined with proxies for convection such as outgoing longwave radiation (OLR). However, upper-tropospheric water vapor (UTWV) gives a more complete picture of tropical circulations because it is more sensitive to the drying and warming associated with subsidence. Previous studies examined tropical variability using relatively short (3–7 yr) UTWV datasets. Intersatellite calibration of data from the High Resolution Infrared Radiation Sounder (HIRS) has recently produced a homogeneous 32-yr climate data record of UTWV for 200–500 hPa. This study explores the utility of HIRS UTWV for identifying the MJO and equatorial waves.

Spectral analysis shows that the MJO and equatorial waves stand out above the low-frequency background in UTWV, similar to previous findings with OLR. The fraction of variance associated with the MJO and equatorial Rossby waves is actually greater in UTWV than in OLR. Kelvin waves, on the other hand, are overshadowed in UTWV by horizontal advection from extratropical Rossby waves.

For the MJO, UTWV identifies subsidence drying in the subtropics, poleward of the convection. These dry anomalies are associated with the MJO’s subtropical Rossby gyres. MJO events with dry anomalies over the central North Pacific Ocean also amplify the 200-hPa flow pattern over North America 7 days later. These events cannot be identified using equatorial OLR alone, which demonstrates that UTWV is a useful supplement for identifying the MJO, equatorial waves.

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Jon Gottschalck, Paul E. Roundy, Carl J. Schreck III, Augustin Vintzileos, and Chidong Zhang

Abstract

An international field campaign, Dynamics of the Madden Julian Oscillation (DYNAMO), took place in the Indian Ocean during October 2011–March 2012 to collect observations for the Madden–Julian oscillation (MJO), especially its convective initiation processes. The large-scale atmospheric and oceanic conditions during the campaign are documented here. The ENSO and the Indian Ocean dipole (IOD) states, the monthly mean monsoon circulation and its associated precipitation, humidity, vertical and meridional/zonal overturning cells, and ocean surface currents are discussed. The evolution of MJO events is described using various fields and indices that have been used to subdivide the campaign into three periods. These periods were 1) 17 September–8 December 2011 (period 1), which featured two robust MJO events that circumnavigated the global tropics with a period of less than 45 days; 2) 9 December 2011–31 January 2012, which contained less coherent activity (period 2); and 3) 1 February–12 April 2012, a period that featured the strongest and most slowly propagating MJO event of the campaign (period 3). Activities of convectively coupled atmospheric Kelvin and equatorial Rossby (ER) waves and their interaction with the MJO are discussed. The overview of the atmospheric and oceanic variability during the field campaign raises several scientific issues pertaining to our understanding of the MJO, or lack thereof. Among others, roles of Kelvin and ER waves in MJO convective initiation, convection-circulation decoupling on the MJO scale, applications of MJO filtering methods and indices, and ocean–atmosphere coupling need further research attention.

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Philip J. Klotzbach, Eric C. J. Oliver, Ronald D. Leeper, and Carl J. Schreck III

Abstract

The winter of 2014/15 brought record snow totals to portions of southeastern New England. Additionally, over 90% of Boston Logan Airport snowfall during the winter fell during phases 7 and 8 of the Madden–Julian oscillation (MJO) index. This motivated the authors to investigate potential connections between intense southeastern New England snowstorms and the MJO in the historical record. It was found that southeastern New England snowfall, measured since the 1930s at several stations in the region, recorded higher than average winter snowfalls when enhanced MJO convection was located over the western Pacific and the Western Hemisphere (phases 7–8). Similarly, snowfall was suppressed when enhanced MJO convection was located over the Maritime Continent (phases 4–5). The MJO also modulates the frequency of nor’easters, which contribute the majority of New England’s snowfall, as measured by reanalysis-derived cyclone tracks. These tracks were more numerous during the same MJO phases that lead to enhanced snowfall, and they were less common during phases with less snowfall.

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Scott E. Stevens, Carl J. Schreck III, Shubhayu Saha, Jesse E. Bell, and Kenneth E. Kunkel

Abstract

Motor vehicle crashes remain a leading cause of accidental death in the United States, and weather is frequently cited as a contributing factor in fatal crashes. Previous studies have investigated the link between these crashes and precipitation typically using station-based observations that, while providing a good estimate of the prevailing conditions on a given day or hour, often fail to capture the conditions present at the actual time and location of a crash. Using a multiyear, high-resolution radar reanalysis and information on 125,012 fatal crashes spanning the entire continental United States over a 6-yr period, we find that the overall risk of a fatal crash increases by approximately 34% during active precipitation. The risk is significant in all regions of the continental United States, and it is highest during the morning rush hour and during the winter months.

Open access
Anthony Arguez, Anand Inamdar, Michael A. Palecki, Carl J. Schreck, and Alisa H. Young

Abstract

Climate normals are traditionally calculated every decade as the average values over a period of time, often 30 years. Such an approach assumes a stationary climate, with several alternatives recently introduced to account for monotonic climate change. However, these methods fail to account for interannual climate variability [e.g., El Niño–Southern Oscillation (ENSO)] that systematically alters the background state of the climate similar to climate change. These effects and their uncertainties are well established, but they are not reflected in any readily available climate normals datasets. A new high-resolution set of normals is derived for the contiguous United States that accounts for ENSO and uses the optimal climate normal (OCN)—a 10-yr (15 yr) running average for temperature (precipitation)—to account for climate change. Anomalies are calculated by subtracting the running means and then compositing into 5 ENSO phase and intensity categories: Strong La Niña, Weak La Niña, Neutral, Weak El Niño, and Strong El Niño. Seasonal composites are produced for each of the five phases. The ENSO normals are the sum of these composites with the OCN for a given month. The result is five sets of normals, one for each phase, which users may consult with respect to anticipated ENSO outcomes. While well-established ENSO patterns are found in most cases, a distinct east–west temperature anomaly pattern emerges for Weak El Niño events. This new product can assist stakeholders in planning for a broad array of possible ENSO impacts in a changing climate.

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Thomas A. Green Jr., Carl J. Schreck III, Nathan S. Johnson, and Sonya Stevens Heath

Abstract

In the early days of television, most weathercasters lacked formal training in meteorology and instead relied on forecasts from other sources. Over the decades, degreed meteorologists became more common. A third category has recently emerged: people with certificates in broadcast meteorology from Mississippi State University (MSU). This certification and the related broadcast meteorology degrees from MSU provide weathercasters with an understanding of meteorology without advanced calculus or differential equations. This study makes no judgment on how a weathercaster’s education background might affect their on-air presentations but notes these courses are required by most guidelines for meteorological degrees, as well as the American Meteorological Society's Certified Broadcast Meteorologist (CBM) program.

This study conducts a unique survey of television meteorologists using the education history listed on their station's website or LinkedIn. The backgrounds of 421 meteorologists were examined with the equivalent of a 94% response rate. Overall, 21% had a broadcast meteorology degree or certification from MSU, 64% had a traditional meteorology degree from MSU or another institution, 2% minored in meteorology or had military training, and 12% listed no or a partial education background in the field. Another way of viewing the data is that the MSU broadcast program alone has nearly as many graduates as the four largest traditional programs combined in our sample. These results were further broken down for various subsets of weathercasters, resulting in statistically significant variations by market size, region, ownership group, and gender.

Open access
Stephanie C. Herring, Nikolaos Christidis, Andrew Hoell, James P. Kossin, Carl J. Schreck III, and Peter A. Stott

Editors note: For easy download the posted pdf of the Explaining Extreme Events of 2016 is a very low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.

Open access
Stephanie C. Herring, Nikolaos Christidis, Andrew Hoell, James P. Kossin, Carl J. Schreck III, and Peter A. Stott
Open access