Xiaoqin Jing

The Impact of Ground-Based Glaciogenic Seeding on Orographic Clouds and Precipitation: A Multisensor Case Study

AbstractA case study is presented from the 2012 AgI Seeding Cloud Impact Investigation, an experiment conducted over the Sierra Madre in southern Wyoming to study the impact of ground-based glaciogenic seeding on precipitation. In this case, on 21 February, the temperature in the turbulent boundary layer above cloud base in the target region was just below −8°C, the target orographic clouds contained liquid water, and the storm was rather steady during the measurement period, consisting of an untreated period, followed by a treated period. Eight silver iodide (AgI) generators were used, located on the windward mountain slope. This study is unprecedented in its diversity of radar systems, which included the W-band (3 mm) profiling Wyoming Cloud Radar (WCR), a pair of Ka-band (1 cm) profiling Micro Rain Radars (MRRs), and an X-band (3 cm) scanning Doppler-on-Wheels (DOW) radar. The WCR was on board a research aircraft flying geographically fixed tracks, the DOW was located on the main mountain pass in the t...

The impact of ground‐based glaciogenic seeding on clouds and precipitation over mountains: A case study of a shallow orographic cloud with large supercooled droplets

This paper examines the impact of ground-based glaciogenic seeding on a shallow, lightly precipitating orographic cloud with rather large (~35 µm) supercooled droplets. The storm was observed on 22 February 2012 as part of the AgI (silver iodide) Seeding Cloud Impact Investigation experiment in Wyoming. The cloud base (top) temperature was about −5°C (−12°C). Vertical velocity data from an airborne Doppler W-band (3 mm) profiling Wyoming Cloud Radar (WCR) indicate broad ascent due to the strong wind (20 m s-1) impinging on the terrain and small pockets of intense updrafts. The large droplets, low droplet and ice particle concentrations, and strong updrafts lead to natural snow growth mainly by accretion (riming). The treated (seeded) period is compared with the preceding untreated period. The main target site, located on a mountain pass, was impacted by AgI seeding, according to a trace chemistry analysis of the falling snow. Data from three radar systems were used in the analysis of the impact of seeding on snow growth: the WCR, two Ka-band (1.2 cm) profiling Micro Rain Radars , and an X-band (3 cm) scanning polarization Doppler-on-Wheels radar. This case is complicated somewhat by a natural increase in cloud liquid water and in snow growth by riming, starting halfway during the seeding period, and continuing after seeding ended. Composite data from the centimeter-wave radar systems indicate an increase in low-level reflectivity during seeding, even after accounting for the natural trend observed in the upwind control region. A precipitation particle probe at the main target site shows an increase in concentration of both small and large hydrometeors.

Dual-Polarization Radar Data Analysis of the Impact of Ground-Based Glaciogenic Seeding on Winter Orographic Clouds. Part I: Mostly Stratiform Clouds

AbstractThe impact of ground-based glaciogenic seeding on wintertime orographic, mostly stratiform clouds is analyzed by means of data from an X-band dual-polarization radar, the Doppler-on-Wheels (DOW) radar, positioned on a mountain pass. This study focuses on six intensive observation periods (IOPs) during the 2012 AgI Seeding Cloud Impact Investigation (ASCII) project in Wyoming. In all six storms, the bulk upstream Froude number below mountaintop exceeded 1 (suggesting unblocked flow), the clouds were relatively shallow (with bases below freezing), some liquid water was present, and orographic flow conditions were mostly steady. To examine the silver iodide (AgI) seeding effect, three study areas are defined (a control area, a target area upwind of the crest, and a lee target area), and comparisons are made between measurements from a treated period and those from an untreated period. Changes in reflectivity and differential reflectivity observed by the DOW at low levels during seeding are consistent...

Dual-Polarization Radar Data Analysis of the Impact of Ground-Based Glaciogenic Seeding on Winter Orographic Clouds. Part II: Convective Clouds

AbstractThis second paper of a two-part series aims to explore the ground-based glaciogenic seeding impact on wintertime orographic clouds using an X-band dual-polarization radar. It focuses on three cases with shallow to moderately deep orographic convection that were observed in January–February of 2012 as part of the AgI Seeding Cloud Impact Investigation (ASCII) project over the Sierra Madre in Wyoming. In each of the storms the bulk upstream Froude number exceeded 1, suggesting unblocked flow. Low-level potential instability was present, explaining orographic convection. The clouds contained little supercooled liquid water on account of the low cloud-base temperature. Ice-crystal photography shows that snow mainly grew by diffusion and aggregation. To examine the seeding effect of silver iodide (AgI), five study areas are defined: two target areas and three control areas. Comparisons are made between the control and target areas as well as between a treated, or seeded, period and an untreated period....

Understanding Heavy Lake-Effect Snowfall: The Vertical Structure of Radar Reflectivity in a Deep Snowband over and downwind of Lake Ontario

AbstractThe distribution of radar-estimated precipitation from lake-effect snowbands over and downwind of Lake Ontario shows more snowfall in downwind areas than over the lake itself. Here, two nonexclusive processes contributing to this are examined: the collapse of convection that lofts hydrometeors over the lake and allows them to settle downwind; and stratiform ascent over land, due to the development of a stable boundary layer, frictional convergence, and terrain, leading to widespread precipitation there. The main data sources for this study are vertical profiles of radar reflectivity and hydrometeor vertical velocity in a well-defined, deep long-lake-axis-parallel band, observed on 11 December 2013 during the Ontario Winter Lake-effect Systems (OWLeS) project. The profiles are derived from an airborne W-band Doppler radar, as well as an array of four K-band radars, an X-band profiling radar, a scanning X-band radar, and a scanning S-band radar.The presence of convection offshore is evident from dee...

The Extra-Area Effect of Orographic Cloud Seeding: Observational Evidence of Precipitation Enhancement Downwind of the Target Mountain

AbstractThis study uses scanning X-band Doppler on Wheels (DOW) radar data to examine whether ground-based glaciogenic seeding influences orographic precipitation, inadvertently, over the foothills of a mountain ~50 km downwind of the target mountain. The data were collected during seven storms during the 2012 AgI Seeding Cloud Impact Investigation (ASCII-12) campaign in Wyoming. The DOW was located on the Sierra Madre (the target range), with excellent low-level coverage toward the Medicine Bow (the downwind range). To examine the seeding impact, two study areas are designated, both over the foothills of the downwind range: one is directly downwind of the remote silver iodide (AgI) generators (target area), and the other is offset sideways (control area). Comparisons are made between radar reflectivity measurements from a treated period and those from an untreated period. The total treated (untreated) period over seven storms is 14.3 h (21.2 h). Independent measurements of ice nuclei concentrations indic...

Evaluating Seasonal Orographic Precipitation in the Interior Western United States Using Gauge Data, Gridded Precipitation Estimates, and a Regional Climate Simulation

AbstractThere are several high-resolution (1–12 km) gridded precipitation datasets covering the interior western United States. This study cross validates seasonal orographic precipitation estimates from the Snowpack Telemetry (SNOTEL) network; the national hourly multisensor precipitation analysis Stage IV dataset (NCEP IV); four gauge-driven gridded datasets; and a 10-yr, 4-km, convection-permitting Weather Research and Forecasting (WRF) Model simulation. The NCEP IV dataset, which uses the NEXRAD network and precipitation gauges, is challenged in this region because of blockage and lack of low-level radar coverage in complex terrain. The gauge-driven gridded datasets, which statistically interpolate gauge measurements over complex terrain to better estimate orographic precipitation, are challenged by the highly heterogeneous, weather-dependent nature of precipitation in complex terrain at scales finer than can be resolved by the gauge network, such as the SNOTEL network. Gauge-driven gridded precipitat...

Ambient Factors Controlling the Wintertime Precipitation Distribution Across Mountain Ranges in the Interior Western United States. Part I: Insights from Regional Climate Simulations

AbstractThis study analyzes the control of upstream conditions on the distribution of wintertime precipitation across mountain ranges in the interior western United States using 10 winters of high-...