Figure 1.
(a) Region of study (in the black box) in context of southeastern United States map; (b) Overview of Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and CloudSat overpasses over the study region. Note the CALIPSO daytime tracks are represented by red dotted lines and the nighttime ones by the blue dotted lines. The CloudSat daytime tracks are indicated by orange lines. From left to right, the three ground ceilometer stations are located at Andrews Murphey Airport (KRHP, marked by the pink triangle), Asheville Airport (KAVL, marked by the green circle), and Jefferson Ashe County Airport (KGEV, marked by the pink triangle). White asterisks denote the locations of four ground fog collectors at Elkmont (ELK), Clingmans Dome (CD), Purchase Knob (PK), and Purchase Knob Tower (PKT).
Figure 1.
(a) Region of study (in the black box) in context of southeastern United States map; (b) Overview of Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and CloudSat overpasses over the study region. Note the CALIPSO daytime tracks are represented by red dotted lines and the nighttime ones by the blue dotted lines. The CloudSat daytime tracks are indicated by orange lines. From left to right, the three ground ceilometer stations are located at Andrews Murphey Airport (KRHP, marked by the pink triangle), Asheville Airport (KAVL, marked by the green circle), and Jefferson Ashe County Airport (KGEV, marked by the pink triangle). White asterisks denote the locations of four ground fog collectors at Elkmont (ELK), Clingmans Dome (CD), Purchase Knob (PK), and Purchase Knob Tower (PKT).
Figure 2.
Schematic of merging the CALIOP cloud base height (CBH) using the L2 333-m cloud layer product and the Cloud Profiling Radar (CPR) CBH from the geometrical profile product (2B-GEOPROF).
Figure 2.
Schematic of merging the CALIOP cloud base height (CBH) using the L2 333-m cloud layer product and the Cloud Profiling Radar (CPR) CBH from the geometrical profile product (2B-GEOPROF).
Figure 3.
Diurnal cycles of fog occurrences in each season (spring: April-May-June, summer: July-August-September, fall: October–November–December, and winter: January–February–March) sampled by fog collectors at PK (a), PKT (b), and CD (c). Note the elevation of each site is denoted in parentheses after its name and the corresponding observation period is indicated at the top of each plot.
Figure 3.
Diurnal cycles of fog occurrences in each season (spring: April-May-June, summer: July-August-September, fall: October–November–December, and winter: January–February–March) sampled by fog collectors at PK (a), PKT (b), and CD (c). Note the elevation of each site is denoted in parentheses after its name and the corresponding observation period is indicated at the top of each plot.
Figure 4.
(Left) Seasonal histograms of ceilometer cloud base heights (CBHs) at KAVL (a), KGEV (c), and KRHP (e) during June 2006–October 2016. Note the elevation of each site is denoted in parentheses after its name; (Right) Seasonal and diurnal cycles of fog occurrences (visibility < 5/8 Statute Miles) at the corresponding ceilometer sites (KAVL: b; KGEV: d; KRHP: f) during the same period. Note the spring season represents April-May-June, the summer season represents July-August-September, the fall season represents October-November-December, and the winter represents January-February-March.
Figure 4.
(Left) Seasonal histograms of ceilometer cloud base heights (CBHs) at KAVL (a), KGEV (c), and KRHP (e) during June 2006–October 2016. Note the elevation of each site is denoted in parentheses after its name; (Right) Seasonal and diurnal cycles of fog occurrences (visibility < 5/8 Statute Miles) at the corresponding ceilometer sites (KAVL: b; KGEV: d; KRHP: f) during the same period. Note the spring season represents April-May-June, the summer season represents July-August-September, the fall season represents October-November-December, and the winter represents January-February-March.
Figure 5.
Time series of drop size distributions (a) from the meteorological particle spectrometer (MPS), droplet effective radius (re; b) derived from the MPS spectra, and reflectivity profiles (c) from a collocated Micro Rain Radar (MRR) at Elkmont on 1 October 2015. Note the shaded area in (b) highlights the period of fog presence.
Figure 5.
Time series of drop size distributions (a) from the meteorological particle spectrometer (MPS), droplet effective radius (re; b) derived from the MPS spectra, and reflectivity profiles (c) from a collocated Micro Rain Radar (MRR) at Elkmont on 1 October 2015. Note the shaded area in (b) highlights the period of fog presence.
Figure 6.
(
a) Fog droplet spectra using six averaging periods of the MPS data before 14:50 LT (details about the spectra can be referred to
Table 2); (
b) Simulated cumulative rainfall with each spectrum used as the fog input in the model, compared to observations from the raingauge (RG, black dotted line) and MRR (grey dotted line). “MOD-SFI’’ indicates model simulations with the presence of fog, thus activating seeder-feeder interactions (SFI). “MOD-NO FOG” indicates the model simulation without fog.
Figure 6.
(
a) Fog droplet spectra using six averaging periods of the MPS data before 14:50 LT (details about the spectra can be referred to
Table 2); (
b) Simulated cumulative rainfall with each spectrum used as the fog input in the model, compared to observations from the raingauge (RG, black dotted line) and MRR (grey dotted line). “MOD-SFI’’ indicates model simulations with the presence of fog, thus activating seeder-feeder interactions (SFI). “MOD-NO FOG” indicates the model simulation without fog.
Figure 7.
Time series of observed reflectivity (
a) from the MRR, simulated reflectivity (
b) with the presence of fog (FOG #4, see its spectrum in
Figure 6a) during 15:00–15:30 LT, and surface wind speed (
c) observed by the weather station (WXT). The black horizontal line in (
a) marks the top boundary level at 1.3 km AGL. The black vertical lines in (
b) mark 14:49 LT and 15:10 LT, which will be discussed in later figure.
Figure 7.
Time series of observed reflectivity (
a) from the MRR, simulated reflectivity (
b) with the presence of fog (FOG #4, see its spectrum in
Figure 6a) during 15:00–15:30 LT, and surface wind speed (
c) observed by the weather station (WXT). The black horizontal line in (
a) marks the top boundary level at 1.3 km AGL. The black vertical lines in (
b) mark 14:49 LT and 15:10 LT, which will be discussed in later figure.
Figure 8.
(Top) Contribution of coalescence and breakup processes to changes in simulated droplet number concentrations at three different heights (350-, 150-, 10-m above ground level (AGL)) in the simulation column before (14:59 LT; (a)) and after (15:10 LT; (b)) the activation of SFI in the model. (Bottom) Enlarged plots for 14:59 LT (c) and 15:10 LT (d) at 10 m AGL.
Figure 8.
(Top) Contribution of coalescence and breakup processes to changes in simulated droplet number concentrations at three different heights (350-, 150-, 10-m above ground level (AGL)) in the simulation column before (14:59 LT; (a)) and after (15:10 LT; (b)) the activation of SFI in the model. (Bottom) Enlarged plots for 14:59 LT (c) and 15:10 LT (d) at 10 m AGL.
Figure 9.
(Top) Time series of simulated drop size distributions at four different heights (clockwise: 500-, 300-, 100-, 10-m AGL). The black vertical lines in (a–d) mark 14:49 LT and 15:10 LT. (Bottom) Simulated rain droplet spectra at 14:59 LT (e) and 15:10 LT (f) at 500-, 300-, 100-, 10-m AGL.
Figure 9.
(Top) Time series of simulated drop size distributions at four different heights (clockwise: 500-, 300-, 100-, 10-m AGL). The black vertical lines in (a–d) mark 14:49 LT and 15:10 LT. (Bottom) Simulated rain droplet spectra at 14:59 LT (e) and 15:10 LT (f) at 500-, 300-, 100-, 10-m AGL.
Figure 10.
Probability distributions using 10-year (June 2006–October 2016) observations of CBHs from: (a) the ground ceilometer at KAVL (elevation: 0.65 km) around daytime overpass (~14:50 LT); (b) the ground ceilometer at KGEV (elevation: 0.97 km) around daytime overpass (~14:45 LT); (c) the ground ceilometer at KRHP (elevation: 0.52 km) around nighttime overpass (~3:45 LT); (d) the merged CALIOP-CPR CBHs for daytime cases at KAVL; (e) the merged CALIOP-CPR CBHs for daytime cases at KGEV; (f) the averaged CALIOP CBHs at 30-km horizontal scale for nighttime cases at KRHP. Note the total number of observation days is denoted in parentheses after each season (spring: April–June, summer: July–September, fall: October–December, and winter: January–March) and the elevation of each site is denoted in parentheses after its name in (a–c).
Figure 10.
Probability distributions using 10-year (June 2006–October 2016) observations of CBHs from: (a) the ground ceilometer at KAVL (elevation: 0.65 km) around daytime overpass (~14:50 LT); (b) the ground ceilometer at KGEV (elevation: 0.97 km) around daytime overpass (~14:45 LT); (c) the ground ceilometer at KRHP (elevation: 0.52 km) around nighttime overpass (~3:45 LT); (d) the merged CALIOP-CPR CBHs for daytime cases at KAVL; (e) the merged CALIOP-CPR CBHs for daytime cases at KGEV; (f) the averaged CALIOP CBHs at 30-km horizontal scale for nighttime cases at KRHP. Note the total number of observation days is denoted in parentheses after each season (spring: April–June, summer: July–September, fall: October–December, and winter: January–March) and the elevation of each site is denoted in parentheses after its name in (a–c).
Figure 11.
(Top) Mean (a) of CALIOP-CPR CBHs (km, AGL) for low-level clouds and fog (LLCF, merged CBH < 4 km MSL) and the corresponding coefficient of variance (CV; b) in each grid box (0.1° × 0.1°) for daytime overpasses. (Bottom) Mean (c) of CALIOP CBHs (km, AGL) for LLCF (CALIOP CBH < 4 km MSL) and the corresponding CV (d) in each grid box (0.1° × 0.1°) for nighttime overpasses. Contour lines denote terrain elevation of 500 m (solid grey), 1000 m (solid black) and 1500 m (dotted black). Note the three ground ceilometer sites (from left to right: KRHP, KAVL, KGEV) are marked by purple crosses and the numbers next to them represent mean ceilometer CBHs around satellite overpass time.
Figure 11.
(Top) Mean (a) of CALIOP-CPR CBHs (km, AGL) for low-level clouds and fog (LLCF, merged CBH < 4 km MSL) and the corresponding coefficient of variance (CV; b) in each grid box (0.1° × 0.1°) for daytime overpasses. (Bottom) Mean (c) of CALIOP CBHs (km, AGL) for LLCF (CALIOP CBH < 4 km MSL) and the corresponding CV (d) in each grid box (0.1° × 0.1°) for nighttime overpasses. Contour lines denote terrain elevation of 500 m (solid grey), 1000 m (solid black) and 1500 m (dotted black). Note the three ground ceilometer sites (from left to right: KRHP, KAVL, KGEV) are marked by purple crosses and the numbers next to them represent mean ceilometer CBHs around satellite overpass time.
Figure 12.
Density-colored scatterplots of MODIS cloud top heights (CTHs) at 1-km pixel and the collocated CALIOP CTHs for daytime (a), single-layer clouds only and nighttime (b) observations. The dashed black line represents the 1:1 line.
Figure 12.
Density-colored scatterplots of MODIS cloud top heights (CTHs) at 1-km pixel and the collocated CALIOP CTHs for daytime (a), single-layer clouds only and nighttime (b) observations. The dashed black line represents the 1:1 line.
Figure 13.
Spatial distributions of MODIS LLCF (CTH <5 MSL, single-layer clouds only) occurrences in each grid box (0.05° × 0.05°) during daytime overpasses for each season (spring: April–June; (a) summer: July–September; (b) fall: October–December; (c) and winter: January–March; (d) Contour lines mark terrain elevation of 500 m (solid grey), 1000 m (solid black) and 1500 m (dotted black) and water surface is delineated by white dots. Note the three ground ceilometer sites (from left to right: KRHP, KAVL, and KGEV) are marked by purple crosses and white asterisks in (b) denote the four ground fog collectors (from left to right: ELK, CD, PK, and PKT).
Figure 13.
Spatial distributions of MODIS LLCF (CTH <5 MSL, single-layer clouds only) occurrences in each grid box (0.05° × 0.05°) during daytime overpasses for each season (spring: April–June; (a) summer: July–September; (b) fall: October–December; (c) and winter: January–March; (d) Contour lines mark terrain elevation of 500 m (solid grey), 1000 m (solid black) and 1500 m (dotted black) and water surface is delineated by white dots. Note the three ground ceilometer sites (from left to right: KRHP, KAVL, and KGEV) are marked by purple crosses and white asterisks in (b) denote the four ground fog collectors (from left to right: ELK, CD, PK, and PKT).
Figure 14.
Spatial distributions of MODIS LLCF (CTH <5 MSL, confident cloudy only) occurrences in each grid box (0.05° × 0.05°) during nighttime overpasses in each season (spring: April–June; (a) summer: July–September; (b) fall: October–December; (c) and winter: January–March; (d) Contour lines mark terrain elevation of 500 m (solid grey), 1000 m (solid black) and 1500 m (dotted black) and water surface is delineated by white dots. Note the three ground ceilometer sites (from left to right: KRHP, KAVL, and KGEV) are marked by purple crosses.
Figure 14.
Spatial distributions of MODIS LLCF (CTH <5 MSL, confident cloudy only) occurrences in each grid box (0.05° × 0.05°) during nighttime overpasses in each season (spring: April–June; (a) summer: July–September; (b) fall: October–December; (c) and winter: January–March; (d) Contour lines mark terrain elevation of 500 m (solid grey), 1000 m (solid black) and 1500 m (dotted black) and water surface is delineated by white dots. Note the three ground ceilometer sites (from left to right: KRHP, KAVL, and KGEV) are marked by purple crosses.
Figure 15.
Fractional occurrences of collocated MODIS cloud properties of LLCF (single-layer clouds with CTH < 5 km MSL) as a function of ceilometer CBHs at KRHP (a–d), KAVL (e–h), and KGEV (i–l) during June 2006–October 2016 (daytime overpasses only). Note the elevation of each site is denoted in parentheses after its name. In each panel, CWP represents cloud water path, COT represents cloud optical thickness, and CER represents cloud particle effective radius.
Figure 15.
Fractional occurrences of collocated MODIS cloud properties of LLCF (single-layer clouds with CTH < 5 km MSL) as a function of ceilometer CBHs at KRHP (a–d), KAVL (e–h), and KGEV (i–l) during June 2006–October 2016 (daytime overpasses only). Note the elevation of each site is denoted in parentheses after its name. In each panel, CWP represents cloud water path, COT represents cloud optical thickness, and CER represents cloud particle effective radius.
Table 1.
Descriptions of the fog collectors and their deployment periods in the Southern Appalachian Mountains (SAM).
Table 1.
Descriptions of the fog collectors and their deployment periods in the Southern Appalachian Mountains (SAM).
Site Name | Latitude | Longitude | Elevation (m) | Fog Observation Period |
---|
Purchase Knob (PK) | 35.586 | −83.073 | 1495 | 1 June 2013–19 May 2015 |
Purchase Knob Tower (PKT) | 35.588 | −83.065 | 1485 | 4 July 2013–5 October 2015 |
Clingmans Dome (CD) | 35.562 | −83.497 | 1956 | 1 June–10 September 2014 |
Elkmont (ELK) | 35.665 | −83.590 | 634 | 25 September–10 December 2015 |
Table 2.
Fitting parameters of the negative exponential distribution characterizing the fog droplet spectra and their liquid water content (LWC) for different averaging periods before the onset of the rainfall event on 1 October 2015. Note N0 represents the intercept and Λ represents the slope.
Table 2.
Fitting parameters of the negative exponential distribution characterizing the fog droplet spectra and their liquid water content (LWC) for different averaging periods before the onset of the rainfall event on 1 October 2015. Note N0 represents the intercept and Λ represents the slope.
| Avg. Period | Dmax (μm) | N0 (cm−3 μm−1) | Λ (μm−1) | LWC (g/m3) |
---|
FOG #1 | 1 min | 50 | 0.59 | 0.11 | 0.0104 |
FOG #2a | 10 min | 50 | 0.37 | 0.11 | 0.006 |
FOG #2b | 10 min | 100 | 0.37 | 0.11 | 0.0074 |
FOG #3 | 13 min | 50 | 2.15 | 0.17 | 0.0064 |
FOG #4 | 15 min | 50 | 4.37 | 0.18 | 0.0101 |
FOG #5 | 17 min | 50 | 3.75 | 0.19 | 0.0085 |
FOG #6 | 20 min | 50 | 2.95 | 0.18 | 0.0078 |
Table 3.
Contingency tables and correlation coefficients (r) of ceilometer cloud base heights (CBHs) at KAVL and daytime satellite retrieved CBHs using the following products: averaged CALIOP Level 2 cloud layer product (333-m CBHs) at 5-, 10-, 20-, 30-, and 40-km horizontal scale; merged CALIOP-CPR CBHs using 10- and 20-km averaging scales for the CALIOP data, following the method outlined in
Figure 2. Values in parentheses are expressed as a percentage of the total number of observation pairs (last column of the table). Note the 5-min window centered over the satellite overpass time is applied to obtain the matched ceilometer CBHs at KAVL.
Table 3.
Contingency tables and correlation coefficients (r) of ceilometer cloud base heights (CBHs) at KAVL and daytime satellite retrieved CBHs using the following products: averaged CALIOP Level 2 cloud layer product (333-m CBHs) at 5-, 10-, 20-, 30-, and 40-km horizontal scale; merged CALIOP-CPR CBHs using 10- and 20-km averaging scales for the CALIOP data, following the method outlined in
Figure 2. Values in parentheses are expressed as a percentage of the total number of observation pairs (last column of the table). Note the 5-min window centered over the satellite overpass time is applied to obtain the matched ceilometer CBHs at KAVL.
| Correct Detection | False Alarm | Missed Detection | Correct Rejection | Correlation Coef. (r) | Total # Pairs |
---|
CALIOP (5 km) | 38 (19%) | 2 (1%) | 60 (30%) | 101 (50%) | 0.50 | 201 |
CALIOP (10 km) | 47 (24%) | 2 (1%) | 51 (25%) | 101 (50%) | 0.52 | 201 |
CALIOP (20 km) | 64 (32%) | 9 (4%) | 34 (17%) | 94 (47%) | 0.56 | 201 |
CALIOP (30 km) | 66 (33%) | 15 (7%) | 32 (16%) | 88 (44%) | 0.51 | 201 |
CALIOP (40 km) | 69 (34%) | 21 (11%) | 29 (14%) | 82 (41%) | 0.50 | 201 |
Merged (10 km) | 70 (35%) | 5 (2%) | 28 (14%) | 98 (49%) | 0.61 | 201 |
Merged (20 km) | 86 (43%) | 12 (6%) | 12 (6%) | 91 (45%) | 0.66 | 201 |
Table 4.
Contingency tables and correlation coefficients (r) of ceilometer CBHs at KGEV and daytime satellite retrieved CBHs using the following products: averaged CALIOP Level 2 cloud layer product (333-m CBHs) at 5-, 10-, 20-, 30-, and 40-km horizontal scale; merged CALIOP-CPR CBHs using 20- and 30-km averaging scales for the CALIOP data, following the method outlined in
Figure 2. Values in parentheses are expressed as a percentage of the total number of observation pairs (last column of the table). Note the 20-min window centered over the satellite overpass time is applied to obtain the matched ceilometer CBHs at KGEV.
Table 4.
Contingency tables and correlation coefficients (r) of ceilometer CBHs at KGEV and daytime satellite retrieved CBHs using the following products: averaged CALIOP Level 2 cloud layer product (333-m CBHs) at 5-, 10-, 20-, 30-, and 40-km horizontal scale; merged CALIOP-CPR CBHs using 20- and 30-km averaging scales for the CALIOP data, following the method outlined in
Figure 2. Values in parentheses are expressed as a percentage of the total number of observation pairs (last column of the table). Note the 20-min window centered over the satellite overpass time is applied to obtain the matched ceilometer CBHs at KGEV.
| Correct Detection | False Alarm | Missed Detection | Correct Rejection | Correlation Coef. (r) | Total # Pairs |
---|
CALIOP (5 km) | 58 (28%) | 4 (2%) | 70 (33%) | 79 (37%) | 0.38 | 211 |
CALIOP (10 km) | 61 (29%) | 6 (3%) | 67 (32%) | 77 (36%) | 0.36 | 211 |
CALIOP (20 km) | 77 (36%) | 6 (3%) | 51 (25%) | 77 (36%) | 0.49 | 211 |
CALIOP (30 km) | 90 (43%) | 12 (6%) | 38 (18%) | 71 (33%) | 0.52 | 211 |
CALIOP (40 km) | 95 (45%) | 18 (9%) | 33 (15%) | 65 (31%) | 0.47 | 211 |
Merged (20 km) | 100 (47%) | 8 (4%) | 28 (13%) | 75 (36%) | 0.59 | 211 |
Merged (30 km) | 110 (52%) | 14 (7%) | 18 (8%) | 69 (33%) | 0.63 | 211 |
Table 5.
Contingency tables and correlation coefficients (r) of ceilometer CBHs at KRHP and nighttime satellite retrieved CBHs using different horizontal averaging scales (5-, 10-, 20-, 30-, and 40-km) of CALIOP Level 2 cloud layer product (333-m CBHs). Values in parentheses are expressed as a percentage of the total number of observation pairs (last column of the table). Note the 20-min window centered over the satellite overpass time is applied to obtain the matched ceilometer CBHs at KRHP.
Table 5.
Contingency tables and correlation coefficients (r) of ceilometer CBHs at KRHP and nighttime satellite retrieved CBHs using different horizontal averaging scales (5-, 10-, 20-, 30-, and 40-km) of CALIOP Level 2 cloud layer product (333-m CBHs). Values in parentheses are expressed as a percentage of the total number of observation pairs (last column of the table). Note the 20-min window centered over the satellite overpass time is applied to obtain the matched ceilometer CBHs at KRHP.
| Correct Detection | False Alarm | Missed Detection | Correct Rejection | Correlation Coef. (r) | Total # Pairs |
---|
CALIOP (5 km) | 41 (20%) | 8 (4%) | 70 (33%) | 90 (43%) | 0.22 | 209 |
CALIOP (10 km) | 44 (21%) | 8 (4%) | 67 (32%) | 90 (43%) | 0.32 | 209 |
CALIOP (20 km) | 63 (30%) | 31 (15%) | 48 (23%) | 67 (32%) | 0.38 | 209 |
CALIOP (30 km) | 76 (36%) | 43 (21%) | 35 (17%) | 55 (26%) | 0.47 | 209 |
CALIOP (40 km) | 77 (37%) | 47 (22%) | 34 (16%) | 51 (25%) | 0.43 | 209 |