Vertical moisture profile characteristics of severe surface drought and surface wetness in the western United States: 1973–2002

Garrity, Colleen M.; Cerveny, Randall S.; Wentz, Elizabeth A.

doi:10.1002/joc.1944

Cited by 3 publications

(2 citation statements)

References 49 publications

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“…Juang et al (Juang et al 2007) found that convective precipitation over moist soils was typically greater in intensity and led to higher precipitation accumulation than for events over dry soil conditions. Garrity et al (Garrity et al 2010) studied the impact of extreme wet and dry regions over the western United States on atmospheric moisture profiles from reanalysis data. They found that the decrease of moisture during drought conditions was limited to below 700 mb and suggest that this may indicate that thunderstorms are playing a role in modulating droughts.…”

Section: Conceptual Model and Discussionmentioning

confidence: 98%

Impacts of Land–Atmosphere Feedbacks on Deep, Moist Convection on the Canadian Prairies

2011

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The purpose of this study was to focus on how anomalies in the normalized difference vegetation index (NDVI; a proxy for soil moisture) over the Canadian Prairies can condition the convective boundary layer (CBL) so as to inhibit or facilitate thunderstorm activity while also considering the role of synoptic-scale forcing. This study focused on a census agricultural region (CAR) over central Alberta for which we had observed lightning data (proxy for thunderstorms), remotely sensed NDVI data, and in situ rawinsonde data (to quantify impacts of vegetation vigor on the CBL characteristics) for 11 summers from 1999 to 2009. The authors' data suggest that the occurrence of lightning over the study area is more likely (and is of longer duration) when storms develop in an environment in which the surface and upper-air synoptic-scale forcing are synchronized. On days when surface forcing and midtropospheric ascent are present, storms are more likely to be triggered when NDVI is much above average, compared to when NDVI is much below average. Additionally, the authors found the response of thunderstorm duration to NDVI anomalies to be asymmetric. That is, the response of lightning duration to anomalies in NDVI is marked when NDVI is below average but is not necessarily discernible when NDVI is above average. The authors propose a conceptual model, based largely on observations, that integrates all of the above findings to describe how a reduction in vegetation vigor-in response to soil moisture deficits-modulates the partitioning of available energy into sensible and latent heat fluxes at the surface, thereby modulating lifting condensation level heights, which in turn affect lightning activity.

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Section: Conceptual Model and Discussionmentioning

confidence: 98%

Impacts of Land–Atmosphere Feedbacks on Deep, Moist Convection on the Canadian Prairies

2011

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“…Discriminant analysis is a statistical technique that objectively classifies categories on the basis of a set of variables. Comparison with the objective classification derived from the linear combination of a set of variables reveals the extent to which an a priori classification scheme which might have been subjectively derived is reproducible [e.g., Diab et al ., ; Michailidou et al ., ; Garrity et al ., ]. Using the below 600 m agl wind speed maximum, above‐core wind shear and below‐core wind shear as the discriminating variables (the same as those presented in the LLJ detection scheme; Table ), the technique was used to objectively reclassify the profiles into the two classes.…”

Section: Llj Detection Criteriamentioning

confidence: 99%

The low-level jet dust emission mechanism in the central Sahara: Observations from Bordj-Badji Mokhtar during the June 2011 Fennec Intensive Observation Period

Allen

Washington

2014

J. Geophys. Res. Atmos.

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This paper presents the first detailed analysis of low-level jets (LLJs) in the central Sahara from ground-based observations at Bordj-Badji Mokhtar, Algeria, and addresses their operation as a dust emission mechanism. On LLJ mornings, composite wind speeds in the core (300 m aboveground level) reach 13.5 m s À1 at 0400. Surface temperatures increase from 0545 (30 min after sunrise), and jet decay begins around 0600. Ten meter winds lag those in the core by 5 h; peak 10 m wind speed, 7.5 m s À1 , occurs at 0900. Only the deepest and strongest LLJs lead to dust emission. At 0600, these five LLJs have core wind speeds ≥16 m s À1 , below-core wind shear ≥ 0.6 m s À1 /30 m, and wind shear between the core and 500 m above the core ≤À1.8 m s À1 . On these occasions, momentum mixes down from the LLJ after surface heating, leading to emission. On nondusty LLJ mornings, the convective boundary layer is 100 m shallower, and the LLJ is too weak to provide enough momentum to be mixed down for emission. LLJs are most frequently embedded in the monsoon flow or in the Harmattan; there is a clear association with the Saharan Heat Low. ERA-Interim reanalysis underestimates both Harmattan and monsoon LLJ core winds (by 4 m s À1 and 6 m s À1 , respectively). The Met Office Africa Limited Area Model underestimates Harmattan LLJ core winds by only 0.2 m s À1 . Monsoon LLJ core winds, however, are underestimated by 8.5 m s À1 . Surface winds at 0900 are underestimated in both cases by up to 6 m s À1 .

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A Meteorological Analysis of Important Contributors to the 1999–2005 Canadian Prairie Drought

Hryciw

Atallah

Milrad

et al. 2013

Monthly Weather Review

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Drought is a complex natural hazard that is endemic to the Canadian prairies. The 1999–2005 Canadian prairie drought, which had great socioeconomic impacts, was meteorologically unique in that it did not conform to the traditional persistent positive Pacific–North American (PNA) pattern and west coast ridging paradigm normally associated with prairie drought. The purpose of this study is to diagnose the unique synoptic-scale mechanisms responsible for modulating subsidence during this drought. Using 30-day running means of the percent of normal precipitation from station data, key severe dry periods during 1999–2005 are identified. Analysis of the mean fields from reanalysis data shows that these dry events can be grouped into three upper-level flow categories: amplified warm, amplified cold, and zonal. Amplified warm cases match the traditional ridging paradigm, while amplified cold and zonal cases elucidate the fact that cold-air advection and downsloping flow, respectively, can also be important subsidence mechanisms during a Canadian prairie drought. In all, the 1999–2005 drought was more meteorologically complex on the synoptic scale than previous historic prairie droughts. Finally, a brief historical perspective shows that the drought was centered in 2001–02 and was not as severe as historical droughts, suggesting that societal vulnerability also played a substantial role in the impacts of the 1999–2005 drought.

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Vertical moisture profile characteristics of severe surface drought and surface wetness in the western United States: 1973–2002

Cited by 3 publications

References 49 publications

Impacts of Land–Atmosphere Feedbacks on Deep, Moist Convection on the Canadian Prairies

Impacts of Land–Atmosphere Feedbacks on Deep, Moist Convection on the Canadian Prairies

The low-level jet dust emission mechanism in the central Sahara: Observations from Bordj-Badji Mokhtar during the June 2011 Fennec Intensive Observation Period

A Meteorological Analysis of Important Contributors to the 1999–2005 Canadian Prairie Drought

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