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Tom Rickenbach published an article in April 2016.
Distribution of Articles published per year
(2003 - 2016)
(2003 - 2016)
Total number of journals
Article 0 Reads 2 Citations A Further Look at Q 1 and Q 2 from TOGA COARE Published: 01 April 2016
Meteorological Monographs, doi: 10.1175/amsmonographs-d-15-0002.1
Two features of Yanai et al.’s profiles of Q1 and Q2—the commonly observed double-peak structure to Q2 and an inflection in the Q1 profile below the melting level—are explored using estimates of convective and stratiform rainfall partitioning based on Massachusetts Institute of Technology (MIT) radar reflectivity data collected during TOGA COARE. The MIT radar data allow the Q1 and Q2 profiles to be classified according to stratiform rain fraction within the radar domain and, within the limitations of the datasets, allow interpretations to be made about the relative contributions of convective and stratiform precipitation to the mean profiles. The sorting of Q2 by stratiform rain fraction leads to the confirmation of previous findings that the double-peak structure in the mean profile is a result of a combination of separate contributions of convective and stratiform precipitation. The convective contribution, which has a drying peak in the lower troposphere, combines with a stratiform drying peak aloft and low-level moistening peak to yield a double-peak structure. With respect to the inflection in the Q1 profile below the 0°C level, this feature appears to be a manifestation of melting. It is the significant horizontal dimension of the stratiform components of tropical convective systems that yields a small but measurable imprint on the large-scale temperature and moisture stratification upon which the computations of Q1 and Q2 are based. The authors conclude, then, that the rather subtle features in the Q1/Q2 profiles of Yanai et al. are directly linked to the prominence of stratiform precipitation within tropical precipitation systems.
Article 0 Reads 0 Citations A seasonal and diurnal climatology of precipitation organization in the southeastern United States Published: 22 January 2015
Quarterly Journal of the Royal Meteorological Society, doi: 10.1002/qj.2500
This paper describes results from a new four‐year (2009–2012) radar‐based precipitation climatology for the southeastern United States (SE US). The climatology shows that a size‐based classification between mesoscale precipitation features (MPF) and isolated precipitation reveals distinct seasonal and diurnal variability of precipitation. On average, from 70%‐90% of precipitation is associated with MPF, generally less in the summertime and in southern coastal regions. MPF precipitation has a relatively small seasonal cycle except in Florida and the warm offshore waters of the Gulf Stream. In contrast, isolated precipitation has a dramatic seasonal cycle that outlines the SE US coastline whereas the MPF precipitation does not, consistent with a thermodynamic mechanism for onshore isolated storms in coastal regions. In summer, the isolated precipitation preferentially forms offshore at night, and dramatically “flips” inland by early afternoon. In contrast, MPF precipitation has no clear diurnal variations except in the southern coastal region in the summer, likely associated with sea breeze convection organized on the mesoscale. These results suggest that the MPF versus isolated precipitation system framework provides a useful basis for future studies of large scale and local controls on precipitation and resulting implications for long‐range predictability of precipitation.
Article 0 Reads 3 Citations Radar Observations of Convective System Variability in Relationship to African Easterly Waves during the 2006 AMMA Speci... Published: 01 December 2009
Monthly Weather Review, doi: 10.1175/2009mwr2740.1
A radar-based analysis of the structure, motion, and rainfall variability of westward-propagating squall-line mesoscale convective systems (SLMCSs) in Niamey, Niger, during the African Monsoon Multidisciplinary Activities (AMMA) 2006 special observing period is combined with an analysis of 700-mb (hPa) winds and relative vorticity to study the relationship between SLMCSs and African easterly waves (AEWs). Radar results show that SLMCSs were the most important rainmakers in Niamey and accounted for about 90% of the rainfall despite being present less than 17% of the time. Analysis of the 700-mb synoptic-scale flow revealed that during the 2006 West African monsoon season the African easterly jet vacillated between about 10° and 15°N on time scales of 1–2 weeks. AEWs followed the jet as it vacillated north and south, thereby producing two preferred paths for AEWs propagating past Niamey’s longitude, a northern track along 8°–16°N and a southern track along 2°–6°N. It was found that Niamey SLMCSs occurred westward of the trough of AEWs propagating along either track. The properties of SLMCSs must then be placed in the context of their location relative to these two AEW tracks, rather than in the trough and ridge pattern of a single AEW track. Radar analysis further indicated that although the total amounts of rainfall produced by SLMCSs occurring in both African easterly jet latitude regimes were similar, significant structural differences occurred between the two groups of systems. SLMCSs that formed to the west of AEW troughs propagating along the northern track had a significantly larger mean stratiform rain fraction in an environment of lower convective available potential energy when compared with the SLMCSs that occurred to the west of the troughs of AEWs in the southern track. The authors conclude that AEWs that propagated farther north provided a more favorable environment for stratiform rain production in Niamey SLMCSs than those AEWs located farther south. These results may be helpful to studies of the two-way interaction between AEWs and convection in West Africa.
Article 0 Reads 6 Citations Radar-observed squall line propagation and the diurnal cycle of convection in Niamey, Niger, during the 2006 African Mon... Published: 12 February 2009
Journal of Geophysical Research, doi: 10.1029/2008jd010871
 Surface radar observations near Niamey, Niger, during the African Monsoon Multidisciplinary Analyses (AMMA) campaign in 2006 documented the structure, motion, and precipitation of cloud systems during the monsoon season. These unique observations for that part of the Sahel were combined with satellite rain estimates and infrared satellite imagery to study the diurnal cycle of rainfall in Niamey, Niger. This study confirms the bimodal structure of the diurnal rainfall cycle in Niamey during AMMA, seen by previous studies of West African rainfall. Radar analysis of squall line mesoscale convective systems (SLMCS) and non‐MCS isolated convection clearly demonstrated that the nocturnal maximum was associated with the observed arrival time of westward propagating SLMCS. Satellite imagery suggested that these SLMCS formed in elevated terrain to the east of Niamey the prior afternoon. Radar observations showed that local isolated convection produced the smaller afternoon maximum. Early in the monsoon season, locally generated convection produced an afternoon diurnal rainfall maximum that was delayed by several hours compared to midseason when African easterly wave (AEW) activity was much greater. We suggest that the observed greater mean convective inhibition early in the season, perhaps tied to the absence of large‐scale forcing from AEW, played a role in the delayed initiation time.
Article 0 Reads 19 Citations Vertical-Mode Decompositions of 2-Day Waves and the Madden–Julian Oscillation Published: 01 March 2008
Journal of the Atmospheric Sciences, doi: 10.1175/2007jas2314.1
Vertical structures of 2-day waves and the Madden–Julian oscillation (MJO) are projected onto vertical normal modes for a quiescent tropical troposphere. Three modes capture the gross tropospheric structure of 2-day waves, while only two modes are needed to represent most of the baroclinic structure of the MJO. Deep circulations that project onto the first baroclinic mode are associated with deep cumulonimbus and stratiform rainfall. Shallow circulations that project onto higher wavenumber modes are associated with precipitating shallow cumulus and congestus and stratiform rainfall. For both disturbances the horizontal divergence contributed by shallow modes is an important factor in the column-integrated moist enthalpy budget. These modes converge moist static energy for a time prior to when deep circulations export moist static energy. These results highlight the importance of properly representing the effects of shallow cumulus, congestus, and stratiform precipitation in theories of convectively coupled waves and in atmospheric models.
Article 0 Reads 7 Citations Variability of South American Convective Cloud Systems and Tropospheric Circulation during January–March 1998 and 1999 Published: 01 May 2003
Monthly Weather Review, doi: 10.1175/1520-0493(2003)131<0961:vosacc>2.0.co;2
A comparison of the submonthly variability of atmospheric circulation and organization of convection in South America during January–February–March of 1998 (JFM98) and January–February–March of 1999 (JFM99) is presented. According to the National Centers for Environmental Prediction reanalysis, the South American low-level jet (SALLJ) was about twice as strong during JFM of the 1998 El Niño episode than during JFM of the 1999 La Niña episode. The difference in SALLJ strength between these two years translated into stronger transport of moist tropical air into the subtropics during JFM98 than during JFM99. An objective tracking technique was used to identify large, long-lived convective cloud systems in infrared imagery. The stronger SALLJ was accompanied by larger and more numerous long-lived convective cloud systems and nearly twice as much rainfall in subtropical South America (parts of southern Brazil, Uruguay, and Argentina) during JFM98 than during JFM99. The difference between JFM98 and JFM99 SALLJ strength in Bolivia is in part explained by submonthly variability associated with the South Atlantic convergence zone (SACZ). Periods when the SACZ is present are marked by southerly or weak northerly winds in Bolivia. The South Atlantic convergence zone was more prominent during JFM99 than during JFM98 contributing to a weaker SALLJ during JFM99. Large, long-lived convective cloud systems in subtropical South America tended to occur during times when the SACZ was absent and the SALLJ was strong over Bolivia. Interannual variability associated with the El Niño–Southern Oscillation also contributed to the observed interannual variability of the SALLJ in Bolivia. In the tropical portions of South America nearly 6 times more large, long-lived convective cloud systems were observed during JFM99 than during JFM98. This was accompanied by more plentiful precipitation in portions of the Amazon basin and in the Bolivian Altiplano during JFM99 than during JFM98. Interannual variability associated with the El Niño–Southern Oscillation was an important contributor to the observed convective cloud system and precipitation differences in tropical South America.